Dissertations / Theses on the topic 'Fluoride glasses Thermal properties'

Neste trabalho, a técnica de Lente Térmica (LT) foi usada para determinar o valor absoluto da difusividade térmica (D), da condutividade térmica (K) e do coeficiente de temperatura do caminho óptico (ds/tD) de vidros fluoretos dopados com cobalto e neodímio, calcogenetos, calcohaletos (mistura de calcogenetos com haletos), aluminate de cálcio e de um cristal fluoreto. Estas medidas foram efetuadas na temperatura ambiente e próxima de Tg para algumas amostras. Para o vidro ZBLAN, realizamos experimentos de LT da temperatura ambiente até ~ 330°C, observando um grande decréscimo de D na região de transição do vidro (Tg ~ 290°C). Nós também aplicamos a técnica de LT para determinar a eficiência quântica fluorescente do ZBLAN dopado com Nd+3. A utilidade desta técnica para determinar as propriedades termo-ópticas dos materiais transparentes em função da temperatura foi demonstrado.
In this work the Thermal Lens (TL) technique was used to determine the absolute values of the thermal diffusivity (D), thermal conductivity (K) and temperature coefficient of the optical path length (ds/dT) of fluoride, chalcogenide, chalcohalide (chalcogenides and halides mixture) and calcium aluminate glass and of a fluoride cristal. These measurements were developed at ambient temperature and near Tg for some samples. For the ZBLAN glass, we performed the TL experiment from ambient to ~ 330°C, observing na abrupt decrease on D close to the glass transition temperature (Tg ~ 290°C). We also applied the TL technique to determine the fluorescence quantum efficiency of Nd+3 doped ZBLAN. The usefulness of this technique to determine thermo-optical properties of transparent materials as a function of the temperature was demonstrated.

Many modern technologies are enabled by the use of thin films and/or nanostructured composite materials. For example, many thermoelectric devices, solar cells, power electronics, thermal barrier coatings, and hard disk drives contain nanostructured materials where the thermal conductivity of the material is a critical parameter for the device performance. At the nanoscale, the mean free path and wavelength of heat carriers may become comparable to or smaller than the size of a nanostructured material and/or device. For nanostructured materials made from semiconductors and insulators, the additional phonon scattering mechanisms associated with the high density of interfaces and boundaries introduces additional resistances that can significantly change the thermal conductivity of the material as compared to a macroscale counterpart. Thus, better understanding and control of nanoscale heat conduction in solids is important scientifically and for the engineering applications mentioned above. In this dissertation, I discuss my work in two areas dealing with nanoscale thermal transport: (1) I describe my development and advancement of important thermal characterization tools for measurements of thermal and thermoelectric properties of a variety of materials from thin films to nanostructured bulk systems, and (2) I discuss my measurements on several materials systems done with these characterization tools. First, I describe the development, assembly, and modification of a time-domain thermoreflectance (TDTR) system that we use to measure the thermal conductivity and the interface thermal conductance of a variety of samples including nanocrystalline alloys of Ni-Fe and Co-P, bulk metallic glasses, and other thin films. Next, a unique thermoelectric measurement system was designed and assembled for measurements of electrical resistivity and thermopower of thermoelectric materials in the temperature range of 20 to 350 °C. Finally, a commercial Anter Flashline 3000 thermal diffusivity measurement system is used to measure the thermal diffusivitiy and heat capacity of bulk materials at high temperatures. With regards to the specific experiments, I examine the thermal conductivity and interface thermal conductance of two different types of nanocrystalline metallic alloys of nickel-iron and cobalt-phosphorus. I find that the thermal conductivity of the nanocrystalline alloys is reduced by a factor of approximately two from the thermal conductivity measured on metallic alloys with larger grain sizes. With subsequent molecular dynamics simulations performed by a collaborator, and my own electrical conductivity measurements, we determine that this strong reduction in thermal conductivity is the result of increased electron scattering at the grain boundaries, and that the phonon component of the thermal conductivity is largely unchanged by the grain boundaries. We also examine four complex bulk metallic glass (BMG) materials with compositions of Zr₅₀Cu₄₀Al₁₀, Cu_46.25Zr_44.25Al_7.5Er₂, Fe₄₈Cr₁₅Mo₁₄C₁₅B₆Er₂, and Ti_41.5Zr_2.5Hf₅Cu_42.5Ni_7.5Si₁. From these measurements, I find that the addition of even a small percentage of heavy atoms (i.e. Hf and Er) into complex disordered BMG structures can create a significant reduction in the phonon thermal conductivity of these materials. This work also indicates that the addition of these heavy atoms does not disrupt electron transport to the degree with which thermal transport is reduced.
Ph. D.

La deposició física de vapor ha sorgit recentment com una ruta alternativa per preparar vidres d’un ampli ventall d'estabilitats, juntament amb altres característiques. Concretament, ha fet possible l’obtenció de vidres amb propietats que superen les dels vidres convencionals i que, d’altra manera, requeririen temps de desenes a diversos milers d'anys de refredament lent o envelliment. És per aquesta raó que aquests vidres s’anomenen vidres de gran estabilitat o bé vidres ultraestables. S’ha demostrat com, per a moltes molècules orgàniques i bones formadores de vidre, la temperatura de dipòsit juga una paper fonamental a l’hora de determinar les propietats del vidre, com són l’estabilitat tèrmica, la densitat o l’orientació molecular entre altres, donant així la possibilitat d’incrementar l'inherent inestabilitat del vidres. Els vidres dipositats a partir de la fase vapor ofereixen tant noves perspectives als fenomen de transició vítria com també aplicacions potencials dins de diversos processos tecnològics, com és el cas de l’electrònica orgànica. Aquest treball té per objectiu aprofundir en el coneixement dels vidres dipositats utilitzant molècules orgàniques semiconductores. Per això, fem servir dues tècniques basades en membranes suspeses—la nanocalorimetria quasi-adiabàtica i ultra-ràpida de rastreig i el mètode 3ω-Völklein—per caracteritzar diversos aspectes d'aquests vidres. En primer lloc, mostrem que les capes amorfes més estables s’obtenen quan són evaporades sobre un substrat al 85 % de temperatura de transició vítria () del material en qüestió. Seguidament, mostrem com aquestes capes dipositades es transformen en vidre sota-refredat en forma d’un front de creixement que es propaga des de les regions altament mòbils (superfície i interfícies). Les característiques d'aquest mecanisme s’investiguen i es discuteixen respecte a les diferents propietats del vidre preparat. En tercer lloc, demostrem com aquesta transformació heterogènia es pot suprimir de manera eficaç quan la interfície amb la mobilitat més alta és bloquejada per una capa amb mobilitat més baixa, obtenint d’aquesta manera accés a la transformació homogènia en tot el volum. A més a més, veiem com l’estabilitat cinètica d’aquestes capes tapades millora quan utilitzem aquesta estratègia. Després de caracteritzar la transició vítria, també mesurem la conductivitat tèrmica d'aquestes capes. Observem com la conductivitat tèrmica en la direcció del pla canvia en funció de la temperatura de dipòsit, un comportament que atribuïm a variacions en l’orientació molecular. Finalment, presentem un senzill díode orgànic d’emissió de llum (OLED) fosforescent consistent tan sols de dues capes orgàniques, per comprovar la influència que la temperatura de dipòsit té en el rendiment del dispositiu. Demostrem com l’eficiència i temps de vida útil del dispositiu milloren quan les seves capes funcionals s’evaporen a . Aquests resultats s’aconsegueixen considerant només la temperatura de transició vítria i, per tant, en principi es poden generalitzar a qualsevol dispositiu OLED. Aquest treball contribueix al coneixement actual dels vidres dipositats a partir de la fase vapor aportant tant noves perspectives sobre les seves propietats tèrmiques i mecanismes de devitrificació com un exemple exitós sobre l’aplicació en els dispositius d'OLED moderns.
Physical vapour deposition has recently emerged as an alternative route to prepare glasses that span a broad range of stabilities, together with other features. Particularly, it is possible to achieve glasses with properties that outperform conventional glasses, and that would otherwise require times from tenths to several thousands of years of slowly-cooling or ageing. For this reason, these glasses are referred as highly stable glasses or ultrastable glasses. In particular, it has been shown that for many molecular organic glass-formers, the deposition temperature plays a crucial role in determining glass properties, such as thermal stability, density or molecular orientation among others, giving the possibility to enhance the inherent instability of glasses. Vapour-deposited glasses offer new insights into the glass transition phenomenon but also potential applications in many technological processes such as in organic electronics. This work is committed to further deepen the knowledge on vapour-deposited glasses using organic semiconductor materials. We use two silicon nitride membrane-based techniques---fast-scanning quasi-adiabatic nanocalorimetry and the 3ω-Völklein method---to characterise several facets of these glasses. Firstly, we show that the most stable amorphous films are obtained when evaporated at 85 % of its corresponding glass transition temperature (). Secondly, we show how vapour-deposited films transform into the supercooled liquid via a propagating growth front that starts at the highly-mobile regions (surface and interfaces). The characteristics of this mechanism are examined and rationalised regarding the different glass properties. Thirdly, we demonstrate how this heterogeneous transformation can be effectively suppressed when the high-mobility interface is capped with a lower mobility layer, gaining access to the bulk transformation. We see how the kinetic stability of the capped layers is improved using this strategy. After characterising the glass transition, we look at the thermal conductivity of these glasses. We observe how the in-plane thermal conductivity changes with the deposition temperature and we attribute this behaviour to variations in the molecular alignment. Finally, we present a simple phosphorescent organic light-emitting diode device (OLED), consisting only of two organic layers, to check the influence of the deposition temperature on the device performance. We demonstrate how its efficiency and lifetime are enhanced when its functional layers are evaporated at 0.85. These results are achieved considering only the glass transition temperature and, therefore, they could be generalised to any OLED device. This work contributes to the existing knowledge of vapour-deposited glasses by providing new insights into their thermal properties and devitrification mechanisms and by exploring their potential application in the state-of-the-art OLED devices.

This thesis concerns and combines the results of experimental studies of magnetocaloric, multiferroic and spin-glass materials, using SQUID magnetometry as the main characteriza-tion technique.  The magnetocaloric effect offers an interesting new technology for cooling and heating applications. The studies of magnetocaloric materials in this thesis are focused on experimen-tal characterization of fundamental magnetic properties of Fe2P-based materials. These are promising magnetocaloric materials with potential industrial use. It is found that the magneto-caloric properties of Fe2P can be optimally tuned by substitution of manganese for iron and silicon for phosphorus. Furthermore, a simple device to measure the magnetocaloric effect in terms of the adiabatic temperature change was constructed.  Materials that simultaneously exhibit different types of ferroic order, for example magnetic and electrical order, are rare in nature. Among these multiferroic materials, those in which the ferroelectricity is magnetically-induced, or vice versa the magnetism is electrically-induced, are intensively studied due to a need for new functionalities in future data storage and logic devices. This thesis presents results on two materials: Co3TeO6 and Ba3NbFe3Si2O14, which belong to the group of magnetically-induced ferroelectrics and exhibit strong coupling be-tween the magnetic and the electrical order parameter. Their ordering properties were studied using magnetic and electrical measurement techniques. The coupling between the magnetic and electronic degrees of freedom was investigated using high-field and low-temperature Raman spectroscopy.  Spin-glass materials exhibit complex magnetism and disorder. The influence of the spin dimensionality on the low and high magnetic field properties of spin glasses was investigated by studying model Heisenberg, XY and Ising spin-glass systems. Significant differences were found between the non-equilibrium dynamics and the hysteresis behavior of Heisenberg systems compared to those of XY and Ising spin glasses.

Structural integrity and reliability of sealing materials for planar type solid oxide fuel cells (pSOFCs) is key to attaining the required functionality and subsequent commercialisation of such fuel cells. In this thesis a number of different series of alumino-borosilicate glasses containing alkaline earth modifiers, as well as ZnO and La2O3 are studied as potential sealant materials. The glass ceramics derived from these glasses were also studied. Vickers hardness indentation was used to assess the hardness and indentation fracture toughness of these glasses and acoustic measurements were used to determine their moduli. The results reveal a decrease in mechanical properties with modifier additions in all the series except for increasing La2O3 in xSi(20-x)La(Sr) with little variation of mechanical properties in the case of xB(15-x)Zn (10BaO-(15-x)ZnO-15La2O3-5Al2O3-(10+x)B2O3-45SiO2 (X= 2.5, 5, 7.5, 10)) and xSi(20-x)Zn (10BaO-(20-x)ZnO-15La2O3-5Al2O3-10B2O3-(40+x)SiO2 (X=2.5,5,7.5) mol%) hardness. Electrical conductivity of sealing glasses must be lower than 10-4 S cm-1 and or > 104Ω cm. Hence the electrical properties the electrical properties of these glasses were measured using impedance spectroscopy and the results indicated that all of the glass and glass ceramic samples studied are electrically resistive and show promise for use as sealing materials. Another important parameter is the thermal properties where the TEC of the sealing glass must be compatible with the other components because differences in TEC of sealing glasses and adjoining SOFC parts result in mismatch and induce thermal stresses during thermal cycling and this may generate cracks through which gas leakages occur. The TEC of xBa(10-x)Al series (10+x)BaO-5ZnO-20SrO-(10-x)Al2O3-20B2O3-35SiO2 (X= 0, 2, 3, 4, 5) and some of xBa(40-x)Si samples (15+x)BaO-5ZnO-15La2O3-5Al2O3-20B2O3-(40+x)SiO2 (X=2.5,5,7.5, 10) have fall within the requirement for sealing glasses. Apart from the TEC the Tg is also a determining factor as to the suitability or otherwise of a sealing glass to be a promising candidate due to the following reasons: (i) thermal stresses develop below the Tg where the glass is brittle therefore the Tg should be as low as possible; (ii) due to high temperature material degradation research efforts are on to reduce the operating temperatures of SOFCs to enhance materials service life and the opportunity for variety of materials selection to construct the SOFCs components. Heat treating series xB(15-x)Zn, xSi(20-x)Zn and xBa(40-x)Si lead to the formation of lanthanum borosilicate single phase. The evolution of these phase lead to not only increased in conductivity as mentioned above but also in the hardness as they are higher in the glass ceramics. However the TEC of the glass ceramics compared with the parent glasses were slightly lower and its reported in this study that this is a good sign of thermal stability as the TEC did not exhibit the possibility of continues increase.

Neste trabalho apresentamos uma nova classe de vidros de fluoretos de metais pesados (HMF) baseados nos fluoretos de índio (InF3) de composição InSrBaZnGdNa e InSrBaZnGaNa. Realizamos um estudo das propiredades físicas (tais como: índice de refração, temperaturas características e estabilidades) e óticas (absorção, emissão e tempo de vida) de vidros puros e dopados com Nd ou Pr. As propriedades estão comparadas com aquelas dos vidros ZrBaLaAlNa (ZBLAN). A principal característica dos vidros de fluoretos de índios puros é a extensa transmissão no IV (até 8330 nm), maiores que a do ZBLAN (até 6650 nm). Tanto os vidros dopados com Nd como com Pr são materiais promissores para o desenvolvimento de laser com emissões a 1050 e 1320 nm nos vidros de Nd e a 1320 nm no vidro com Pr e amplificadores óticos para telecomunicações na janela ótica centrada a 1300 nm, uma vez que apresentam bandas de emissão a 1315 nm (InSBZnGdN), 1317 nm (InSBZnGdN:Nd) e a 1320 nm (InSBZnGdN:Pr).
We present a new class of heavy metals fluoride glasses (HMF) of InSrBaZnGdNa and InSrBaZnGaNa compositions. We have realized a study of the physical properties such as refraction index, characteristic temperatures, stability and optical properties such as absorption, emission, lifetime of pure, Nd or Pr doped glasses. These properties are similar to those obtained for glasses of ZrBaLaAlNa (ZBLAN) composition. The main characteristic of pure indium fluoride glasses is their larger transmission window in the infrared region (8330 nm) compared to ZBLAN composition (6650 nm). Rare earth doped glasses are promising materials for the development of glasses laser with emission in the 1050-1320 nm range (Nd) and 1320 nm (Pr), as well as optical amplifiers for telecommunication in the optical window centered at 1300 nm, as prominent emission bands are located at 1315 nm (InSBZnGdN), 1317 nm (InSBZnGdN:Nd) and 1320 nm (InSBZnGdN:Pr).

The solid, liquid, and solidification properties of Pd, Ag pure metals and especially PdxAg1-x alloys are studied by using the molecular dynamics simulation. The effects of temperature and concentration on the physical properties of Pdx$Ag1-x are analyzed. Sutton-Chen (SC) and Quantum Sutton-Chen (Q-SC) many-body potentials are used as interatomic interactions which enable one to investigate the thermodynamic, static, and dynamical properties of transition metals. The simulation results such as cohesive energy, density, elastic constants, bulk modulus, pair distribution functions, melting points and phonon dispersion curves obtained for Pd, Ag and PdxAg1-x are in good agreement with the available experimental data at various temperatures. The predicted melting points of Pd, Ag and their binary alloys by using Q-SC potential parameters are closer to experimental values than the ones predicted from SC potential parameters. The liquid properties such as diffusion constants and viscosities computed from Q-SC potentials are also in good agreement with the available experimental data and theoretical calculations. Diffusion coefficients and viscosity results calculated from simulation obey the Arrhenius equation well. The coefficients of the Arrhenius equation are given in order to calculate the self-diffusion coefficient and shear viscosity of Pd-Ag alloys at the desired temperature and concentration. Using different cooling rates, we investigate glass formation tendency and crystallization of Pd-Ag metal alloys, by analyzing pair distribution function, enthalpy, volume, and diffusion coefficient. Pd-Ag alloys show the glass structure at fast cooling rates while it crystallizes at slow cooling rates. Glass and crystallization temperatures are also obtained from the Wendt-Abraham parameter. The split of the second peak in the pair distribution function is associated with the glass transition. Glass forming ability increases with increasing concentration of Ag in Pd-Ag alloys. Thermal and mechanical properties of Cu, Au metals and their ordered intermetallic alloys Cu3 Au(L12), CuAu(L10), and CuAu3(L12) are also studied to investigate the effects of temperature and concentration on the physical properties of Cu-Au alloys. The simulation results such as cohesive energy, lattice parameter, density, elastic constants, bulk modulus, heat capacity, thermal expansion, melting points, and phonon dispersion curves are in good agreement with the available experimental and theoretical data at various temperatures. The Q-SC potential parameters are more reliable in determining physical properties of metals and their random and ordered alloys studied in this work

Made available in DSpace on 2014-10-09T12:35:37Z (GMT). No. of bitstreams: 0
Made available in DSpace on 2014-10-09T14:03:58Z (GMT). No. of bitstreams: 1 18221.pdf: 475984 bytes, checksum: d5ed50df9b4585d0998e12d282f7f294 (MD5)
Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Orientador: Keizo Yukimitu
Banca:João Carlos Silos Moraes
Banca: Valmor Roberto Mastelaro
Banca: Mauro Luciano Baesso
Banca: Tomaz Catunda
Resumo: O desenvolvimento de sistemas e dispositivos ópticos deu origem à área hoje conhecida como fotônica. A busca por novas aplicações ou aprimoramento de sistemas optoeletrônicos tem levado à obtenção de novos materiais vítreos, os quais exigem minuciosa investigação com relação às suas propriedades físicas. Entre os vários sistemas vítreos estudados, os vidros teluritos destacam-se como um dos mais promissores vidros óxidos já desenvolvidos quando comparados com outros vidros clássicos, como os vidros silicatos, fosfatos e boratos. Desta forma, neste trabalho foram preparados vidros com diferentes composições para o sistema Li2O-TeO2-R (R: WO3 e Nb2O5), e caracterizados usando técnicas de análises térmicas, estruturais e ópticas. O estudo das propriedades térmicas é importante na determinação e entendimento do mecanismo de nucleação e crescimento de cristais, sendo, essencial este conhecimento quando o intuito for preparar vidros de alta qualidade exigidos para aplicações tecnológicas. O desenvolvimento tecnológico destes vidros requer que a nucleação intrínseca e o crescimento de cristais sejam suficientemente reduzidos para evitar perdas ópticas. O estudo estrutural destes vidros também é importante para determinação das unidades estruturais constituintes dos vidros. Sabe-se que a adição de metais de transição na matriz telurito provoca a diminuição das unidades TeO3 e aumenta as TeO4, assim, causando aumento da densidade do vidro e, conseqüentemente, aumento no índice de refração. As técnicas utilizadas foram as de análise térmica (DSC), FTIR, XRD, lente térmica (LT) e método de ângulo de Brewster para a obtenção do índice de refração
Abstract: The development of optical systems and devices is the area known as photonics. The search for new applications or improvements of optoelectronic systems has led to the obtaining of new glassy materials, which require thorough investigation with respect to their physical properties. Among the various glass systems studied, the tellurite glasses are presented as one of the most promising oxide glasses that have been developed, when compared with other classics glasses like silicates, phosphates and borates. Thus, in this work were prepared with different glass compositions for the system Li2O-TeO2-R (R: WO3 and Nb2O5) and characterized using techniques of thermal analysis, structural and optical properties. The study of thermal properties is important in determining and understanding the mechanism of nucleation and crystal growth and this knowledge is essential when the purpose is to prepare high-quality glasses required for technological applications. The technological development of these glasses demands sufficiently low intrinsic nucleation and crystal growth to avoid optics losses. The structural study of these glasses is also important for determining the structural units constituting the glass. It is known that the addition of transition metals in the tellurite glass matrix causes a decrease in the TeO3 and increases the TeO4 units and thus causing the increased of density of the glass and, consequently, increasing the refractive index. The techniques used were differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD) and thermal lens (TL) and Brewster angle method for obtaining the refractive index
Doutor

Made available in DSpace on 2014-06-11T19:31:03Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-06-27Bitstream added on 2014-06-13T20:41:14Z : No. of bitstreams: 1 sidel_sm_dr_ilha.pdf: 916747 bytes, checksum: 29e258472ed07d7364e52a3b2739b834 (MD5)
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
O desenvolvimento de sistemas e dispositivos ópticos deu origem à área hoje conhecida como fotônica. A busca por novas aplicações ou aprimoramento de sistemas optoeletrônicos tem levado à obtenção de novos materiais vítreos, os quais exigem minuciosa investigação com relação às suas propriedades físicas. Entre os vários sistemas vítreos estudados, os vidros teluritos destacam-se como um dos mais promissores vidros óxidos já desenvolvidos quando comparados com outros vidros clássicos, como os vidros silicatos, fosfatos e boratos. Desta forma, neste trabalho foram preparados vidros com diferentes composições para o sistema Li2O-TeO2-R (R: WO3 e Nb2O5), e caracterizados usando técnicas de análises térmicas, estruturais e ópticas. O estudo das propriedades térmicas é importante na determinação e entendimento do mecanismo de nucleação e crescimento de cristais, sendo, essencial este conhecimento quando o intuito for preparar vidros de alta qualidade exigidos para aplicações tecnológicas. O desenvolvimento tecnológico destes vidros requer que a nucleação intrínseca e o crescimento de cristais sejam suficientemente reduzidos para evitar perdas ópticas. O estudo estrutural destes vidros também é importante para determinação das unidades estruturais constituintes dos vidros. Sabe-se que a adição de metais de transição na matriz telurito provoca a diminuição das unidades TeO3 e aumenta as TeO4, assim, causando aumento da densidade do vidro e, conseqüentemente, aumento no índice de refração. As técnicas utilizadas foram as de análise térmica (DSC), FTIR, XRD, lente térmica (LT) e método de ângulo de Brewster para a obtenção do índice de refração
The development of optical systems and devices is the area known as photonics. The search for new applications or improvements of optoelectronic systems has led to the obtaining of new glassy materials, which require thorough investigation with respect to their physical properties. Among the various glass systems studied, the tellurite glasses are presented as one of the most promising oxide glasses that have been developed, when compared with other classics glasses like silicates, phosphates and borates. Thus, in this work were prepared with different glass compositions for the system Li2O-TeO2-R (R: WO3 and Nb2O5) and characterized using techniques of thermal analysis, structural and optical properties. The study of thermal properties is important in determining and understanding the mechanism of nucleation and crystal growth and this knowledge is essential when the purpose is to prepare high-quality glasses required for technological applications. The technological development of these glasses demands sufficiently low intrinsic nucleation and crystal growth to avoid optics losses. The structural study of these glasses is also important for determining the structural units constituting the glass. It is known that the addition of transition metals in the tellurite glass matrix causes a decrease in the TeO3 and increases the TeO4 units and thus causing the increased of density of the glass and, consequently, increasing the refractive index. The techniques used were differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD) and thermal lens (TL) and Brewster angle method for obtaining the refractive index

Metallic glasses possess attractive properties, such as high strength, good corrosion resistance, and superior soft magnetic performance. They also serve as precursors for synthesizing nanocrystalline materials. In addition, a new class of composites having crystalline phases embedded in amorphous matrix is evolving based on selective crystallization of metallic glasses. Therefore, crystallization of metallic glasses and its effects on properties has been a subject of interest. Previous investigations from our research group related to laser assisted crystallization of Fe-Si-B metallic glass (an excellent soft magnetic material by itself) showed a further improvement in soft magnetic performance. However, a fundamental understanding of crystallization and mechanical performance of laser treated metallic glass was essential from application point of view. In light of this, the current work employed an integrated experimental and computational approach to understand crystallization and its effects on tensile behavior of laser treated Fe-Si-B metallic glass. The time temperature cycles during laser treatments were predicted using a finite element thermal model. Structural changes in laser treated Fe-Si-B metallic glass including crystallization and phase evolution were investigated with the aid of X-ray diffraction, differential scanning calorimetry, resistivity measurements, and transmission electron microscopy. The mechanical behavior was evaluated by uniaxial tensile tests with an InstronTM universal testing machine. Fracture surfaces of the metallic glass were observed using scanning electron microscopy and site specific transmission electron microscopy. Fe-Si-B metallic glass samples treated with lower laser fluence (<0.49 J/mm2) underwent structural relaxation while higher laser flounces led to partial crystallization. The crystallization temperature experienced an upward shift due to rapid heating rates of the order of 104 K/s during laser treatments. The heating cycle was followed by termination of laser upon treatment attainment of peak temperature and rapid cooling of the similar order. Such dynamic effects resulted in premature arrest of the crystallite growth leading to formation of fine crystallites/grain (~32 nm) of α-(Fe,Si) as the major component and Fe2B as the minor component. The structural relaxation, crystallization fractions of 5.6–8.6 Vol% with α-(Fe,Si) as the main component, and crystallite/grain size of the order of 12 nm obtained in laser fluence range of 0.39-0.49 J/mm2 had minimal/no influence on tensile behavior of the laser treated Fe-Si-B metallic glass foils. An increase in laser fluence led to progressive increase in crystallization fractions with considerable amounts of Fe2B (2-6 Vol%) and increase in grain size to ~30 nm. Such a microstructural evolution severely reduced the strength of Fe-Si-B metallic glass. Moreover, there was a transition in fracture surface morphology of laser treated Fe-Si-B metallic glass from vein pattern to chevron pattern. Tensile loading lacked any marked influence on the crystallization behavior of as-cast and structurally relaxed laser-treated metallic glass foils. However, a significant crystallite/grain growth/coarsening of the order of two and half times was observed in the fractured region compared to the region around it for the laser-treated partially crystallized metallic glass foils. The simultaneous effects of stress generation and temperature rise during tensile loading were considered to play a key role in crystallite/grain growth/coarsening.

Silver containing chalcogenide glasses have been extensively studied during the last few decades; the main interest in these materials being their electrical conductivity which changes by several orders of magnitude upon silver doping. Glassy chalcogenides doped with silver have applications in optical elements, gratings, micro-lenses, waveguides, bio & chemical sensors, solid electrolytes, batteries, etc. Chalcohalide glasses have become important in the recent times, from both scientific & technological points of view, due to the interesting properties exhibited by these glasses such as the transparency in the infrared region, the stability against devitrification, solubility of rare earth elements, etc. In this thesis work, the thermal properties and electrical switching behavior of certain silver and iodine doped chalcogenide glasses have been investigated The thesis contains five chapters: Chapter 1: This chapter is an introduction to the fundamental aspects of amorphous semiconductors with a particular reference to chalcogenide glasses. The advantages and applications of chalcogenide glasses are also described. Chapter 2: The methods of preparation and characterization of the glasses investigated are described in this chapter. Also, the details of the experiments undertaken, namely temperature modulated Alternating Differential Scanning Calorimetry (ADSC), electrical switching analysis, Photo-thermal Deflection Spectroscopy (PDS), etc, are outlined. Chapter 3: In this chapter, the thermal behavior and electrical switching of silver doped Ge-Se and As-Se chalcogenide glasses are described. Bulk, melt-quenched Se-rich Ge0.15Se0.85-xAgx glasses have been found to be microscopically phase separated and composed of Ag2Se clusters and GeSe2-Se network. When the silver concentration exceeds 10 atom %, the Ag2Se clusters embedded in the GeSe2-Se network percolate. The signature of this percolation threshold is clearly observed as the sudden appearance of two exothermic crystallization peaks in ADSC runs. Density, molar volume and micro hardness studies also strongly support the view of a percolation transition. The super-ionic conduction observed earlier in these glasses at higher silver proportions, is likely to be connected with the silver phase percolation. It has been found that Ge0.15Se0.85-xAgx glasses of lower silver concentration (x = 0.07 and 0.08) do not exhibit electrical switching at voltages up to 1100 V. A negative resistance behavior and threshold type electrical switching is seen in Ge0.15Se0.85-xAgx samples with x 0.09. Also, fluctuations are observed in the I-V characteristics of these samples, which have been attributed to the difference in thermal conductivities between the Ag2Se inclusions and the Ge-Se base glass. A sharp drop has been observed in the switching voltage with Ag concentration which is due to the more metallic nature of silver and the presence of Ag+ ions. Further, the saturation in the decrease of VT around x = 0.10, is related to silver phase percolation in these glasses. Bulk As20Se80-xAgx glasses (0 x 15) have been found to exhibit two endothermic glass transitions and two exothermic crystallization reactions on heating. Based on which it is suggested that As20Se80-xAgx glasses are also microscopically phase separated, containing Ag2Se phases embedded in an As-Se backbone. The occurrence of microscopic phase separation in As20Se80-xAgx glasses is also confirmed by SEM studies. With increasing silver concentration, the Ag2Se phase percolates in the As-Se matrix, with a well-defined percolation threshold at x = 8. This silver phase percolation is exemplified by sudden jumps in the composition dependence of the second crystallization peak and non-reversible heat-flow, Hnr obtained at the second glass transition reaction of As20Se80-xAgx glasses. The super-ionic conduction observed earlier in these glasses at higher silver proportions, is likely to be associated with the observed silver phase percolation. Like Ge0.15Se0.85-xAgx glasses, As20Se80-xAgx glasses also exhibit threshold type electrical switching with fluctuations in the I-V characteristics; these fluctuations have been attributed to the difference in thermal conductivities between the Ag2Se inclusions and the As-Se base glass. A sharp drop has been observed in the switching voltage with Ag concentration which is due to the more metallic nature of silver and the presence of Ag+ ions. Further, the saturation in the decrease of VT around x = 8, is found to be related to silver phase percolation in these glasses, which has been proposed on the basis of ADSC experiments. Chapter 4: The chapter 4 deals with thermal studies, electrical switching investigations and Photo-thermal Deflection Spectroscopic (PDS) measurements on certain Ge-Te-I and As-Te-I chalcohalide glasses. It has been found that the compositional variation of the glass transition temperature of Ge22Te78-xIx glasses, obtained by Alternating Differential Scanning Calorimetry (ADSC), exhibits a broad hump around 5 atom % of iodine. Further, a sharp minimum is seen in the composition dependence of non-reversing enthalpy (Hnr) of Ge22Te78-xIx glasses at x = 5, which is suggestive of a thermally reversing window at this composition. Electrical switching studies on Ge22Te78-xIx glasses indicate that these glasses exhibit memory type electrical switching. At lower iodine concentrations, a decrease is seen in switching voltages with an increase in iodine content (in comparison with the base Ge22Te78 glass), which is due to the decrease in network connectivity. The increase seen in switching voltages of Ge22Te78-xIx glasses at higher iodine contents, suggests that the influence of the metallicity is stronger at higher iodine proportions. It is also interesting to note that the composition dependence of the threshold voltages shows a slope change at x = 5, the inverse rigidity percolation threshold of the Ge22Te78-xIx system. . Further, it is found that the thermal diffusivities ( D) of Ge22Te78-xIx glasses decrease with the increase in iodine content, which has been understood on the basis of fragmentation of the Ge-Te network with the addition of iodine. Also, a cusp is seen in the composition dependence of thermal diffusivity at the composition x = 5 (average coordination number, r = 2.39), which has been identified to be the inverse rigidity percolation threshold of the system at which the network connectivity is lost. ADSC studies on As45Te55-xIx chalcohalide glasses (3 x 10) reveal that there is not much variation in the glass transition temperature of As45Te55-xIx glasses, even though there is a wide variation in r . Based on this observation we suggest that the variation in glass transition temperature of network glasses is dictated by the variation in average bond energy rather than the average coordination number. Further, the non-reversing enthalpy Hnr of As45Te55-xIx glasses is found to exhibit a sharp minimum at the composition x = 6. A broad hump is also seen in glass transition and crystallization temperatures in the composition range 5 x 7. These results indicate a narrow thermally reversing window in As45Te55-xIx glasses around the composition x = 6. As45Te55-xIx glasses have been found to exhibit a memory to threshold type change in switching behavior with iodine content (x 6), which has been understood on the basis of the sharp increase in thermal diffusivity above x = 6. It is also observed that the switching voltages do not change appreciably with composition/average coordination number. Though no pronounced signature of a stiffness transition is seen in the variation with composition of VT, fluctuations are seen in the switching voltages around x = 6, the composition corresponding to the sharp thermally revering window. PDS studies indicate that the thermal diffusivities () of As45Te55-xIx chalcohalide exhibit a sharp minimum at the composition x = 6. This result reasserts the presence of a sharp thermally reversing window in As45Te55-xIx glasses around the composition x = 6. Chapter 5: The significant results obtained in the present thesis work have been summarized in this chapter. Further, the scope for future work is also presented.

Polymer-derived silicon oxycarbides (SiOC) exhibit improved mechanical properties in comparison to vitreous silica, a unique crystallization resistance and excellent stability in harsh environments. Consequently, silicon oxycarbides are potential candidates for high- temperature applications, for example in ceramic heaters, high-temperature reactors, combustion engines or as part of thermal protection systems. For these applications, the precise knowledge of the mechanical properties like hardness, elasticity and creep, but also of the thermal properties like thermal conductivity and thermal expansion is of paramount interest. In the present study the intrinsic mechanical and thermal properties of silicon oxycarbides were systematically assessed in order to obtain a fundamental understanding concerning the relationship between their phase composition, microstructure and properties. Therefore, a SiOC glass and a series of SiOC glass ceramics with varying compositions were synthesized and carefully characterized. It is demonstrated that the concept of phase separation (i.e. glass vs. glass ceramic) is important in SiOC materials. It has a large impact on thermal expansion, thermal transport and the activation volume carrying deformation at high temperatures (as expressed by the activation energy for creep). Furthermore, it is shown, that upon the proper choice of composition and microstructure, tailored mechanical and thermal properties can be realized within the SiOC system: (i) Increasing amounts of Si-C bonds in SiOC glasses or β-SiC nanoparticles in SiOC glass ceramics leads to an increase of Young’s modulus, indentation hardness, creep resistance and viscosity due to an increase of the glass network connectivity in SiOC glasses and the homogeneous distribution of β-SiC nanoparticles with good mechanical properties, respectively. On the other hand, the incorporation of Si-C bonds reduces the thermal transport in SiOC glasses as lower mass fractal networks and defects/oxygen vacancies are formed. However, amounts > 20 vol.% β-SiC nanoparticles lead to an increase of the thermal transport in SiOC glass ceramics. (ii) The high aspect ratio segregated carbon phase leads to a significant increase in thermal transport as well as in thermal expansion of SiOC materials already for small amounts. It has a moderate influence on Young’s modulus (decrease), creep resistance and viscosity (increase) in comparison to Si-C bonds/β-SiC nanoparticles, whereas hardness remains unbiased. The segregated carbon phase is responsible for the enhanced anelastic recovery of SiOC glass ceramics.

By the investigation of the bulk metallic glass-forming liquids that have very low critical cooling rates, the thermodynamics of metallic glasses can be clarified. For studying thermodynamic properties, such as the specific heat capacity, calorimetry (DSC) is utilized and one of the most used instruments is the differential scanning calorimeter. In this study calorimetry was used to investigate the thermodynamics of the Pd������Ni������Cu������P������ alloy. The specific heat capacity of the liquid and crystalline state, enthalpy, entropy, as well as Gibbs free energy difference between the liquid and crystalline state were measured and evaluated in comparison with previous studies of the alloy. The Pd������Ni������Cu������P������ alloy is known as a metallic glass-forming alloy that has high ability for vitrification without crystallization. By observing the onset of heat flux of the exothermic reactions in the DSC, the time-temperature-transformation diagram can be constructed, and the diagram confirms the high ability for the vitrification for the sample. In addition, the effect of fluxing by B���O��� to reduce heterogeneous nucleation is determined by the TTT-diagram. The enthalpy change during the crystallization was directly measured in experiments in which the sample was held isothermally in the DSC. Both enthalpies, calculated from the specific heat capacity measurements and direct measured enthalpy exactly match each other. The very interesting effect in these experiments is an effect of heat treatment in the samples. Two glass transition temperatures can be noticeably recognized by scanning the exothermic event of the sample with the DSC. The material separates into two undercooled liquids. The two phases that are separated during heat treatment can be described by two different fragility parameters.
Graduation date: 2001

by Chua Lai Fei Joseph.
Thesis (M.Phil.)--Chinese University of Hong Kong, 1996.
Includes bibliographical references.
by Chua Lai Fei Joseph.
ACKNOWLEDGMENTS --- p.2
ABSTRACT --- p.3
Chapter CHAPTER 1: --- INTRODUCTION --- p.5
Chapter 1.1 --- METALLIC GLASS --- p.5
Chapter 1.2 --- SOLIDIFICATION PROCESS OF AN ALLOY --- p.7
Chapter 1.2.1 --- COOLING PATH --- p.7
Chapter 1.2.2 --- FREE VOLUME MODEL --- p.8
Chapter 1.2.3 --- NUCLEATION --- p.9
Chapter 1.2.4 --- LIQUID PHASE SEPARATION --- p.10
Chapter 1.3 --- IDEAS ON SOME CHARACTERISTIC PARAMETER OF GLASS AND GLASS FORMING ABILITY OF AN METALLIC ALLOY --- p.11
Chapter 1.3.1 --- CORRELATION FOR THE EXPANSION COEFFICIENT AND THE GLASS TRANSITION TEMPERATURE --- p.11
Chapter 1.3.2 --- CORRELATION FOR THE GLASS FORMING ABILITY WITH CRYSTALLINE COMPOUNDS/SOLID-SOLUTIONS --- p.12
REFERENCES --- p.13
Chapter CHAPTER 2: --- EXPERIMENTAL --- p.17
Chapter 2.1 --- SAMPLE PREPARATION --- p.17
Chapter 2.2 --- EXPERIMENTAL DETAILS FOR ALPHA MEASUREMENT --- p.17
Chapter 2.3 --- EXPERIMENTAL DETAILS FOR FINDING EQUILIBRIUM PHASES AND GLASS FORMING ABILITY OF AN ALLOY --- p.20
Chapter 2.3.1 --- FINDING EQUILIBRIUM PHASES --- p.20
Chapter 2.3.2 --- FINDING GLASS FORMING ABILITY --- p.21
Chapter CHAPTER 3: --- CORRELATION FOR THERMAL EXPANSION COEFFICIENTS OF MOLTEN GLASS FORMING SYSTEMS --- p.28
REFERENCES --- p.37
Chapter CHAPTER 4: --- CORRELATION FOR THE GLASS FORMING ABILITY OF PD83.5-XCUXSI16.5 WITH CRYSTALLINE COMPOUNDS/SOLID- SOLUTIONS --- p.38
Chapter 4.1 --- INTRODUCTION --- p.39
Chapter 4.2 --- EXPERIMENTAL --- p.39
Chapter 4.3 --- RESULTS --- p.41
Chapter 4.4 --- DISCUSSION --- p.43
REFERENCES --- p.54
Chapter CHAPTER 5: --- CONCLUSION --- p.55

Germanium-Arsenic-Selenium chalcogenide glasses are considered as good candidates for photonic applications due to their excellent transparency in the infrared range and high optical nonlinearities. A deep understanding of composition-structure-property relationship in Ge-As-Se ternary system is thus becoming increasingly important, which can serve as a guideline for materials selection. In this work, the structure and various physical properties of GexAsySe100-x-y bulk glasses have been systematically investigated. Raman spectra and EXAFS measurements reveal that chemically ordered network model can be applied to Selenium-rich glasses, but fails to explain bonding characterization of Selenium-poor compositions. Atomic arrangements are more sensitive to the changes in chemical compositions. A tight association between the fragility and the deviation from stoichiometry has been found in the Ge-As-Se system by differential scanning calorimetry. It is shown that chemical compositions with the lowest values of fragility index are far less likely to incur structural relaxation. Those strong glasses are normally chosen as ideal materials for fabrication of stable photonic devices. The variation of density and elastic modulus as a function of mean coordination number both show two transition thresholds, which correlate with floppy-to-rigid phase transition and 2D-to-3D structure transition respectively. The results provide clear evidence that some physical properties of Ge-As-Se chalcogenide glasses are significantly determined by their mean coordination numbers, but could be further tuned by the chemical compositions. The detailed optical investigation shows that the generalized Miller’s rule is a simple but effective approach to estimate the nonlinearities of a broad variety of chalcogenide glasses. Nonlinear properties of these materials exhibit strong dependence upon their optical bandgap in the near infrared. It seems that the highest nonlinearity at telecommunications wavelengths is predictable in chalcogenide glasses.

A high temperature high vacuum rheometer has been designed, fabricated, and tested for the study of the steady shear viscosity for multicomponent bulk metallic glass forming alloys. This rheometer has an operating range up to 1525 K, rotational frequencies of 9.4*10⁻³-3.7*10¹ radians/s, and a calibrated viscosity range of 9.6*10⁻³ and 1.2*10² Pa*s while maintaining absolute pressures pressure < 1*10⁻⁶ mbar. Zr[subscript 41.2]Ti[subscript 13.8]Cu[subscript 10.0]Ni[subscript 12.5]Be[subscript 22.5] (Vitreloy 1) is reported. The unexpected findings of non-Newtonian behavior above the liquidus temperature were observed. Observations of shear thinning, thixotropic, and viscoelastic behaviors have been made. Our results show that Vitreloy 1 can be modeled as a power law fluid, with a power law exponent of approximately -0.5 for high shear rates. We attribute the non-Newtonian behavior to structural ordering within the melt. The technological and scientific implications for non-Newtonian behavior are discussed.
Graduation date: 2005

Hong Sin Yi, Grace.
Thesis (M.Phil.)--Chinese University of Hong Kong, 1997.
Includes bibliographical references (leaves 50-51).
Acknowledgments
Abstract
Chapter Chapter 1 --- Introduction
Chapter 1.1 --- Metallic Glass and its application --- p.1
Chapter 1.2 --- Glass Forming Ability (GFA) --- p.2
Chapter 1.3 --- Equilibrium Phase --- p.3
Chapter 1.4 --- Nucleation and Growth --- p.6
Chapter 1.5 --- Spinodal Decomposition --- p.8
Chapter 1.6 --- Morphology Comparison between Nucleation and Growth and Spinodal --- p.13
Figures --- p.14
References --- p.24
Chapter Chapter 2 --- Experimental Method
Experimental Method --- p.25
Figure --- p.29
References --- p.30
Chapter Chapter 3 --- Metastable liquid miscibility gap in Pd-Si and its glass forming ability
Introduction --- p.32
Experimental --- p.33
Results --- p.34
Discussion --- p.36
Figures --- p.40
References --- p.49
Bibliography --- p.50

碩士
義守大學
材料科學與工程學系
100
Since the development of the amorphous alloys, most alloys have been formed by the employment of such expensive elements as Au, Pt and Zr. In order to lower the cost and elevate their practicality, experts and scholars, therefore, have started to develop the lower-cost Cu-base amorphous alloy, which has excellent mechanical properties and whose compressive fracture strength can reach above 2000MPa. According to previous documents, the thermal and mechanical properties of the amorphous alloy can be elevated by adding a micro amount of the elements of Si, Pd and Fe. This study utilizes the Cu47Ti34Zr11Ni8 alloy, which has the better glass formation ability, as its base. The result indicates that the thermal properties of the alloy’s base can be elevated by adding the elements Si and Pd. The supercooled liquid region of the Cu47Ti34Zr11Ni4Pd4 alloy is approximately 49K, and the glass formation ability of the Cu47Ti34Zr11Ni4Si4 alloy can elevate the values of Trg and γ to 0.61 and 0.4 respectively. The Cu47Ti34Zr11Ni4Si4 alloy contains the precipitated phase of high hardness, thus causing hardness to rise to approximately 725Hv. The Cu47Ti34Zr11Ni6Fe2 alloy produces the precipitated phase that has the capability of absorbing stress and preventing the crack from advancing, enabling the alloy to possess the maximum fracture toughness about 82MPa m1/2. The fracture strength of the Cu47Ti34Zr11Ni4Si4 alloy is 1900MPa. The low amount and the irregular shape of the precipitated phase cause the stress concentration effect inside the alloy and no plastic strain. The fracture strength of the Cu47Ti34Zr11Ni6Fe2 alloy is 2010MPa. Its precipitated phase disperses unevenly and there is no elevated effect on plastic strain. The fracture strength of the Cu47Ti34Zr11Ni4Pd4 alloy is 1977MPa. Its plastic strain is elevated to about 0.7%, caused by the nano crystalline phase precipitated from the inside of the material.

過去幾十年當中，金屬玻璃（包括塊狀金屬玻璃）中非晶相分離的發生已經成為了一個具有爭議性的課題。一些報告報導在具有負混合熱的Pd-Ni-P合金體系中發生了非晶相分離。然而，有一些報告聲稱相分離不能在Pd-Ni-P非晶合金中被觀察到。文獻分析表明，困難在於缺乏直接的實驗證據。
為了解決這個難題，示差掃描量熱儀、高分辨電子顯微鏡、掃描透射模式下的高角環射暗場相、以及能量色散X射線光譜儀等檢測儀器在我們實驗當中被使用。同時為了清楚展示非晶相分離反應，在過冷Pd₄₁.₂₅Ni₄₁.₂₅P₁₇.₅熔體被冷卻為固態非晶樣品之前引入了中間熱退火處理。
實驗研究了三種經由不同路徑製備的A、B、C型號樣品。結果表明在非晶/液態Pd₄₁.₂₅Ni₄₁.₂₅P₁₇.₅合金中可能存在獨特的短程有序結構，它會導致相分離的發生。同时研究發現，在大約625 K，調幅分解的持續時間的下限大概是200 s。調幅分解的時間常數R在大約625 K 下為0.002 s⁻¹。三种类型样品在不同的溫度下被退火從而獲得部分的結晶。A型號和B型號具有相似的行為。在低溫下，圓形的核心首先形成，接著發生共晶反應。在高溫下，出現了一種形狀為立方體的析出相。在C型號的樣品當中，核心和立方的析出物同時被發現。但是核心的成分分佈與A和B型號中出現的不同。同時，隨著退火時間的加長形核的數量也具有獨特的行為表現。作為對比，Pd₄₀Ni₄₀P₂₀塊狀金屬玻璃的結晶行為也被展開了研究。同樣的，以形成核心開始，但是它的成分分佈異於A和B型號的樣品。
Amorphous phase separation in metallic glass (including bulk metallic glass) has been a controversial issue in the past several decades. There are reports saying that amorphous phase separation occurs in Pd-Ni-P, which has a negative heat of mixing among its constituent elements. However, there are also as many reports claiming that phase separation is absent in amorphous Pd-Ni-P alloys. The lack of direct experimental evidence makes the issue to be difficult to be resolved.
To solve this problem, differential scanning calorimetry (DSC), high resolution transmission electron microscopy (HRTEM), high angle annular dark field (HAADF) in scanning transmission electron microscopy, and energy dispersive X-ray spectroscopy (EDX) have been employed. Intermediate thermal annealing is introduced before an undercooled Pd₄₁.₂₅Ni₄₁.₂₅P₁₇.₅ melt is cooled down to become a solid amorphous specimen.
A-type, B-type, and C-type specimens of composition, Pd₄₁.₂₅Ni₄₁.₂₅ P₁₇.₅, have been prepared via three different cooling paths. It was found that amorphous phase separation indeed occurs in C-type specimens. Results suggest that there may be unique short range orders in amorphous/liquid Pd₄₁.₂₅Ni₄₁.₂₅P₁₇.₅, which are responsible for the phase separation. Experimental arrangements were made to study the occurrence of spinodal reaction in undercooled molten Pd₄₁.₇₅Ni₄₁.₇₅P₁₇.₅ alloys as a function of time. The lower bound of the duration of the spinodal decomposition at a temperature of {U+2248}625 K is about 200 s and the time constant R of the spinodal decomposition at a temperature of {U+2248}625 K is 0.002 s⁻¹.
A-type and B-type specimens have similar crystallization behavior. At low temperature, it starts with the formation of a spherical core and then eutectic crystallization takes over. At higher temperatures, an additional phase in the shape of a cube appears. In annealed C-type specimens, cores and cubic precipitates are also found. However, the composition profile of the cores is different and the number of nucleation events versus time has peculiar characteristics. The crystallization behavior of Pd₄₀Ni₄₀P₂₀ BMG was studied for comparison. It again starts out with the formation of a core, but with a composition profile different from those of A-type and B-type specimens.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Lan, Si = 對於具有負混合熱的塊狀金屬玻璃非晶相分離的研究 / 蘭司.
Thesis (Ph.D.)--Chinese University of Hong Kong, 2012.
Includes bibliographical references.
Abstract also in Chinese.
Lan, Si = Dui yu ju you fu hun he re de kuai zhuang jin shu bo li fei jing xiang fen li de yan jiu / Lan Si.
Abstract of thesis --- p.i
Acknowledgements --- p.v
List of Tables --- p.x
List of Figures --- p.xi
Chapter Chapter 1 --- Introduction and literature review --- p.1
Chapter 1.1 --- Introduction to metallic glasses --- p.1
Chapter 1.1.1 --- Background of metallic glasses --- p.1
Chapter 1.1.2 --- Glass transition --- p.2
Chapter 1.1.3 --- The undercooling of liquids --- p.3
Chapter 1.1.4 --- Crystal nucleation and growth in liquids --- p.3
Chapter 1.1.4.1 --- Crystal Nucleation in liquids --- p.3
Chapter 1.1.4.2 --- Crystal growth in liquids --- p.5
Chapter 1.1.4.3 --- TTT diagram --- p.6
Chapter 1.1.4.4 --- Crystallization in metallic glasses --- p.6
Chapter 1.1.5 --- Glass formation methods and systems --- p.6
Chapter 1.1.6 --- Glass forming ability and criteria --- p.8
Chapter 1.1.7 --- Properties and applications --- p.9
Chapter 1.2 --- The basic theory of phase separation in a binary system --- p.10
Chapter 1.2.1 --- Thermodynamic background --- p.10
Chapter 1.2.2 --- Solid state phase separation --- p.11
Chapter 1.2.2.1 --- A miscibility gap of binary mixture --- p.11
Chapter 1.2.2.2 --- Nucleation and growth mechanism --- p.12
Chapter 1.2.2.3 --- Spinodal decomposition mechanism --- p.13
Chapter 1.2.3 --- Liquid state miscibility gap in a binary system --- p.21
Chapter 1.3 --- Literature review for phase separation in metallic glasses --- p.23
Chapter 1.4 --- The aim of this thesis --- p.28
Figures --- p.30
References --- p.39
Chapter Chapter 2 --- Experiments and characterization --- p.44
Chapter 2.1 --- Introduction and the outline of the experiments --- p.44
Chapter 2.2 --- Sample preparation --- p.45
Chapter 2.2.1 --- Bulk metallic glasses preparation --- p.45
Chapter 2.2.1.1 --- Preparation of clean fused silica tubes --- p.45
Chapter 2.2.1.2 --- Weighing --- p.46
Chapter 2.2.1.3 --- Alloying --- p.46
Chapter 2.2.1.4 --- Fluxing --- p.47
Chapter 2.2.2 --- Thermal annealing --- p.49
Chapter 2.2.3 --- Specimens preparation for characterization --- p.50
Chapter 2.2.3.1 --- Cutting, molding, grinding and polishing --- p.50
Chapter 2.2.3.2 --- Etching --- p.51
Chapter 2.2.3.3 --- Thinning for TEM foils --- p.51
Chapter 2.3 --- Characterization --- p.55
Chapter 2.3.1 --- Differential scanning calorimetry (DSC) --- p.55
Chapter 2.3.2 --- Scanning electron microscopy (SEM) --- p.55
Chapter 2.3.3 --- Transmission electron microscopy (CTEM and HRTEM) --- p.57
Chapter 2.3.4 --- High angle annular dark field (HAADF) in Scanning transmission electron microscopy (STEM) --- p.58
Chapter 2.3.5 --- Energy dispersive X-ray spectroscopy (EDX) --- p.59
Figures --- p.62
References --- p.69
Chapter 3 --- p.70
Chapter 3.1 --- Introduction --- p.70
Chapter 3.2 --- Materials and Experimental --- p.73
Chapter 3.3 --- Results --- p.75
Chapter 3.3.1 --- Thermal behaviors of three types of specimens --- p.75
Chapter 3.3.2 --- Microstructures of three types of specimens --- p.75
Chapter 3.3.2.1 --- A-type specimens --- p.75
Chapter 3.3.2.2 --- B-type specimens --- p.76
Chapter 3.3.2.3 --- C-type specimens --- p.76
Chapter 3.4 --- Discussion --- p.78
Chapter 3.5 --- Conclusions --- p.79
Chapter 3.6 --- Afterward --- p.79
Figures --- p.80
References --- p.89
Chapter Chapter 4 --- The time constant of the spinodal decomposition in Pd₄₁.₇₅Ni₄₁.₇₅P₁₇.₅ bulk metallic glasses --- p.92
Chapter 4.1 --- Introduction --- p.92
Chapter 4.2 --- Materials and experimental --- p.92
Chapter 4.3 --- Results --- p.94
Chapter 4.3.1 --- Thermal behaviors --- p.94
Chapter 4.3.2 --- Microstructures --- p.94
Chapter 4.4 --- Discussion --- p.96
Chapter 4.5 --- Conclusions --- p.98
Figures --- p.100
References --- p.123
Chapter Chapter 5 --- Crystallization in homogeneous and phase-separated Pd₄₁.₂₅Ni₄₁.₂₅P₁₇.₅ bulk metallic glasses --- p.125
Chapter 5.1 --- Introduction --- p.125
Chapter 5.2 --- Experiments --- p.126
Chapter 5.3 --- Results --- p.128
Chapter 5.3.1 --- Low temperature thermal annealing at 613 K with 0≤t{U+2090} ≤ 8 h --- p.128
Chapter 5.3.1.1 --- A-type and B-type specimens --- p.128
Chapter 5.3.1.2 --- C-type specimens --- p.130
Chapter 5.3.1.3 --- Pd₄₀Ni₄₀P₂₀ BMG --- p.132
Chapter 5.3.2 --- High temperature thermal annealing --- p.133
Chapter 5.3.2.1 --- A-type and B-type specimens --- p.133
Chapter 5.3.2.2 --- C-type specimens --- p.135
Chapter 5.3.2.3 --- Pd₄₀Ni₄₀P₂₀ BMG --- p.137
Chapter 5.4 --- Discussion --- p.137
Chapter 5.4.1 --- Formation of spherical cores --- p.138
Chapter 5.4.1.1 --- A-type and B-type Pd₄₁.₇₅Ni₄₁.₇₅P₁₇.₅ specimens --- p.138
Chapter 5.4.1.2 --- C-type Pd₄₁.₇₅Ni₄₁.₇₅P₁₇.₅ specimens --- p.139
Chapter 5.4.1.3 --- Pd₄₀Ni₄₀P₂₀ BMG --- p.140
Chapter 5.4.2 --- Formation of cubic precipitates --- p.141
Tables --- p.142
Figures --- p.144
References --- p.188
Chapter Chapter 6 --- Conclusions --- p.190
Bibliography --- p.192

The absence of long-range order in glassy chalcogenides provides the convenience of changing the elemental ratios and hence the properties over a wide range. The interesting properties exhibited by chalcogenide glasses make them suitable materials for Phase Change Memories (PCM) and other applications such as infrared optical devices, photo-receptors, sensors, waveguides, etc. One of the most remarkable properties of chalcogenides is their electrical switching behavior. Reversible (threshold type) or irreversible (memory type) switching from a high resistance OFF state to a low resistance ON state in glassy chalcogenides occurs at a critical voltage called the threshold/switching voltage (VT). Investigations on the switching behavior and its composition dependence throw light on the local structural effects of amorphous chalcogenide semiconductors and also help us in identifying suitable samples for PCM applications. Thermal analysis by Differential Scanning Calorimetry (DSC) has been extensively used in glass science, particularly for measurements of thermal parameters such as enthalpy of relaxation, specific heat change, etc., near glass transition. Quite recently, the conventional DSC has been sophisticated by employing a composite temperature profile for heating, resulting in the Temperature Modulated DSC (TMDSC) or Alternating DSC (ADSC). Measurements made using ADSC reveal thermal details with enhanced accuracy and resolution, and this has lead to a better understanding of the nature of glass transition. The thermal parameters obtained using DSC/ADSC are also vital for understanding the electrical switching behavior of glassy chalcogenides. The motivation of this thesis was twofold: The first was to develop a novel, high voltage programmable power supply for electrical switching analysis of samples exhibiting high VT, and second to investigate the thermal and electrical switching behavior of certain Se-Te based glasses with Ge and Sb additives. The thesis contains seven chapters: Chapter 1: This chapter provides an overview of amorphous semiconductors (a-SC) with an emphasis on preparation and properties of glassy chalcogenides. The various structural models and topological thresholds of a-SC are discussed with relations to the glass forming ability of materials. The electronic band models and defect states are also dealt with. The essentials of electrical switching behavior of chalcogenides are discussed suggesting the electronic nature of switching and the role of thermal properties on switching. Chapter 2: The second chapter essentially deals with theory and practice of the experimental techniques adopted in the thesis work. The details of the melt-quenching method of synthesizing glassy samples are provided. Considering the importance, the theory of thermal analysis by DSC & ADSC, are discussed in detail, highlighting the advantages of the latter method adopted in the thesis work. The instrumentation and electronics, developed and used for electrical switching analysis are also introduced at a block diagram level. Finally, the methods used for structural analysis are briefed. Chapter 3: This chapter is dedicated to the design and development details of the programmable High Voltage dc Power Supply (HVPS: 1750 V, 45 mA) undertaken in the thesis work. The guidelines used for power supply topology selection, the specifications and block diagram of the HVPS are provided in that sequence. The operation of the HVPS is discussed using the circuit diagram approach. The details of software control are also given. The performance validations of the HVPS, undertaken through voltage & current regulation tests, step & frequency response tests are discussed. Finally, the sample-test results on the electrical switching behavior of representative Al20As16Te64 and Ge25Te65Se10 samples, obtained using both the current & voltage sweep options of the HVPS developed are illustrated. Chapter 4: Results of the thermally induced transitions governed by structural changes which are driven by network connectivity in the GexSe35-xTe65 (17 ≤ x ≤ 25) glasses, as revealed by ADSC experiments, are discussed in this chapter. It is found that the GexSe35-xTe65 glasses with x ≤ 20 exhibit two crystallization exotherms (Tc1 & Tc2), whereas those with x ≥ 20.5, show a single crystallization reaction upon heating (Tc). The glass transition temperature of GexSe35-xTe65 glasses is found to show a linear, but not-steep increase, indicating a progressive and not an appreciable build-up in network connectivity with Ge addition. The exothermic reaction at Tc1 has been found to correspond to the partial crystallization of the glass into hexagonal Te and the reaction at Tc2 is associated with the additional crystallization of rhombohedral Ge-Te phase. It is also found that the first crystallization temperature Tc1 of GexSe35-xTe65 glasses of lower Ge concentrations (with x ≤ 20), increases progressively with Ge content and eventually merges with Tc2 at x = 20.5 ( = 2.41); this behavior has been understood on the basis of the reduction in Te-Te bonds of lower energy and an increase in Ge-Te bonds of higher energy, with increasing Ge content. Chapter 5: This chapter deals with the electrical switching studies on GexSe35-xTe65 (17 ≤ x ≤ 25) glasses, with an emphasis on the role of network connectivity/rigidity on the switching behavior. It is found that the switching voltage (VT) increases with Ge content, exhibiting a sudden jump at x=20, the Rigidity Percolation Threshold (RPT) of the system. In addition, the switching behavior changes from memory to threshold type at the RPT and the threshold switching is found to be repetitive for more than 1500 cycles. Chapter 6: In this chapter, the results of thermal analysis (by ADSC) and electrical switching investigations on SbxSe55-xTe45 (2 ≤ x ≤ 9) are discussed. It is found that the addition of trivalent Sb contributes very meagerly to network growth but directly affects the structural relaxation effects at Tg. Further, SbxSe55-xTe45 glasses exhibit memory type electrical switching, which is understood on the basis of poor thermal stability of the samples. The metallicity factor is observed to outweigh the network factor in the composition dependence of VT of SbxSe55-xTe45 glasses. Chapter 7: The chapter 7 summarizes the results obtained in the thesis work and provides the scope for future work. The references are cited in the text along with the first author’s name and year of publication, and are listed at the end of each chapter in alphabetical order.

Yin, Weixin = 非晶液態鈀-鎳-磷合金相位分離的證據 / 殷瑋欣.
Thesis (M.Phil.)--Chinese University of Hong Kong, 2011.
Includes bibliographical references.
Abstracts in English and Chinese.
Yin, Weixin = Fei jing ye tai ba-nie-lin he jin xiang wei fen li de zheng ju / Yin Weixin.
Acknowledgement --- p.i
Abstract --- p.ii
Contents --- p.iv
Chapter Chapter 1 --- Introduction --- p.1
Chapter 1.1 --- A Brief Introduction to Metallic Glass --- p.1
Chapter 1.2 --- Homogeneous Nucleation Frequency --- p.3
Chapter 1.3 --- Heterogeneous Nucleation Frequency --- p.4
Chapter 1.4 --- Spinodal Decomposition --- p.5
Chapter 1.5 --- Conditions for Metallic Glasses Formation --- p.8
Chapter 1.6 --- How to Get Large Undercooling --- p.9
Chapter 1.7 --- Liquid Phase Separation --- p.10
References --- p.12
Figures --- p.13
Chapter Chapter 2 --- Experimental Procedures and Techniques of Transmission Electron Microscopy --- p.18
Chapter 2.1 --- Sample preparation --- p.18
Chapter 2.1.1 --- Ni2P Preparation --- p.18
Chapter 2.1.2 --- Alloying --- p.18
Chapter 2.1.3 --- Fluxing --- p.18
Chapter 2.2 --- Introduction to TEM Specimen Preparation --- p.19
Chapter 2.2.1 --- "Grinding, Polishing and Punching" --- p.19
Chapter 2.2.2 --- Final Thinning by Ion Miller --- p.20
Chapter 2.2.3 --- Final Thinning by Twin Jet --- p.20
Chapter 2.3 --- Introduction to Transmission Electron Microscopy Techniques --- p.21
Chapter 2.3.1 --- Basic Instrumentations of TEM --- p.21
Chapter 2.3.2 --- Elastic Scattering and Inelastic Scattering --- p.21
Chapter 2.3.3 --- Image Contrast --- p.22
Chapter 2.3.4 --- Dark Field Image and Bright Field Image --- p.24
Chapter 2.3.5 --- EDX Mapping --- p.24
Chapter 2.3.6 --- High Resolution Images --- p.25
References --- p.26
Figures --- p.27
Chapter Chapter 3 --- Evidence of amorphous/liquid phase separation in Pd41.25Ni41.25P17.5 alloy --- p.32
Chapter 3.1 --- Introduction --- p.32
Chapter 3.2 --- Experimental --- p.34
Chapter 3.3 --- Discussions --- p.42
References --- p.44
Figures --- p.45
Chapter Chapter 4 --- Conclusions --- p.68

by Yuen Cheong Wing.
Thesis (M.Phil.)--Chinese University of Hong Kong, 1996.
Includes bibliographical references (leaves [138]-[142]).
by Yuen Cheong Wing.
Acknowledgments --- p.ii
Abstract --- p.iii
Table of Contents --- p.v
Chapter Chapter 1: --- Introduction --- p.1-1
Chapter 1.1 --- What is Metallic Glass? --- p.1-1
Chapter 1.2 --- Use of Metallic Glass --- p.1-3
Chapter 1.3 --- A Dilemma --- p.1-4
Chapter 1.4 --- Glass Forming Ability --- p.1-5
Chapter 1.5 --- Role of Liquid State Phase Separation in GFA --- p.1-6
References --- p.1-9
Figure --- p.1-10
Chapter Chapter 2: --- Phase Separation Theory --- p.2-1
Chapter 2.1 --- Free Energy Curve --- p.2-1
Chapter 2.2 --- Nucleation and Growth --- p.2-2
Chapter 2.2.1 --- Liquid state nucleation and growth --- p.2-2
Chapter 2.2.2 --- Nucleation and growth during solidification --- p.2-4
Chapter 2.3 --- Spinodal Decomposition --- p.2-5
Chapter 2.3.1 --- Cahn-Hilliard linearized equation --- p.2-6
Chapter 2.3.2 --- Temporal evolution --- p.2-9
References --- p.2-12
Figures --- p.2-15
Chapter Chapter 3 ： --- Experimental Setup and Techniques --- p.3-1
Chapter 3.1 --- Technique in Achieving High Undercooling --- p.3 -1
Chapter 3.1.1 --- Effects and limitation of B203 --- p.3-1
Chapter 3.1.2 --- Preparation of B203 --- p.3-3
Chapter 3.1.3 --- Cleansing of apparatus --- p.3-4
Chapter 3.2 --- Experimental --- p.3-5
Chapter 3.2.1 --- Sample preparation --- p.3-6
Chapter 3.2.2 --- Experimental setup --- p.3-7
Chapter 3.2.3 --- Procedures --- p.3-8
Chapter 3.3 --- Observing the Microstructure --- p.3-9
Chapter 3.3.1 --- Cutting --- p.3-10
Chapter 3.3.2 --- Molding --- p.3-10
Chapter 3.3.3 --- Polishing --- p.3-11
Chapter 3.3.4 --- Etching --- p.3-12
Chapter 3.3.5 --- Observation --- p.3-12
References --- p.3-14
Table --- p.3-15
Figures --- p.3-16
Chapter Chapter 4: --- Metastable liquid phase separationin undercooled molten PD40. 5]\l40.5P19 --- p.4-1
Abstract --- p.4-1
References --- p.4-9
Figures --- p.4-10
Chapter Chapter 5 ： --- Transformation in undercooled molten PD40.5NI40.5P19 --- p.5-1
Chapter 5.1 --- Abstract --- p.5-1
Chapter 5.1 --- Introduction --- p.5-2
Chapter 5.3 --- Experimental --- p.5-4
Chapter 5.4 --- Results --- p.5-6
Chapter 5.5 --- Discussions --- p.5-13
References --- p.5-20
Figures --- p.5-22
Chapter Chapter 6 ： --- Solidification of liquid spinodal in undercooled PD40.5NI40.5P19 --- p.6-1
Chapter 6.1 --- Abstract --- p.6-1
Chapter 6.2 --- Introduction --- p.6-2
Chapter 6.3 --- Experimental --- p.6-3
Chapter 6.4 --- Results --- p.6-5
Chapter 6.5 --- Discussions --- p.6-10
References --- p.6-17
Figures --- p.6-18
Chapter Chapter 7: --- Conclusion --- p.7-1
References --- p.7-4
Bibliography --- p.B-1

by Tong Kwok Wang.
Parallel title in Chinese characters.
Thesis (M.Phil.)--Chinese University of Hong Kong, 1990.
Bibliography: leaves 71-74.
Acknowledgement
Abstract
Chapter 1. --- Introduction
Chapter 1.1 --- General Introduction --- p.1
Chapter 1.2 --- Properties --- p.5
Chapter 1.3 --- Background of this research --- p.10
Chapter 1.4 --- The Present Experiment --- p.11
Chapter 2. --- Theory
Chapter 2.1 --- Conduction Mechanism --- p.15
Chapter 2.2 --- Temperature Dependence of Thermal Conductivity --- p.16
Chapter 2.3 --- Phonon Conductivity and phonon mean free path --- p.20
Chapter 3. --- Experimental
Chapter 3.1 --- Thermal Diffusivity by Laser Photothermal Radiometry --- p.22
Chapter 3.2 --- Resistivity Measurement --- p.30
Chapter 3.3 --- Sample Preparation --- p.36
Chapter 3.4 --- Data Analysis --- p.37
Chapter 4. --- Results and Discussion
Chapter 4.1 --- Thermal Conductivity --- p.41
Chapter 4.2 --- Electronic Thermal Conductivity --- p.47
Chapter 4.3 --- Phonon Thermal Conductivity --- p.52
Chapter 4.4 --- Phonon Mean Free Path --- p.58
Chapter 5. --- Conclusion and Suggestions for Further Work --- p.68
References --- p.71
Appendixes --- p.75

碩士
大同大學
材料工程學系(所)
97
The speed of the energy consumption is much fast than before in recent year and the green energy becomes the popular issue at present. And because of improving the efficiency and decreasing the cost, the research, absorbing the solar energy to change into the solar cell, is in progress. Now the silicon solar cell is the main trend on the market. In the process of producing polycrystall silicon thin film, the development of non-silicon substrate (foreign substrate) becomes much important for producing the solar cell of the wide area and declines the dependence of the silicon. For getting the polycrystall silicon thin film of the high-quality to adjust the difference between the thermal expansion coefficients, the surface of the substrate is covered with the interlayer. And for improving the smooth level of the alumina substrate, it is applied to deposit the solar cell of the polycrystall silicon thin film. The research shows that the glasses of m=20,15 ,and A2S2L6 have appropriate thermal expansion coefficient (it’s between alumina substrate (CTE:8.0X10-6/oC) and silicon deposition layer(2.9~3.6X10-6/oC, 20~1200oC)), higher anneal temperature(>800oC), lower stall temperature(<1500oC),and the smooth level of the great smooth layer(Rms<0.5nm), guessing that may be made the interlayer of the glass between the alumina substrate and the silicon deposition layer.

"Apr 2002."
The numerals in title is subscript.
Thesis (Ph.D.)--Chinese University of Hong Kong, 2002.
Includes bibliographical references.
Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web.
Mode of access: World Wide Web.
Abstracts in English and Chinese.

The Phase Change Memories (PCM) based on chalcogenide glasses are being considered recently as a possible replacement for conventional Non Volatile Random Access Memories (NVRAM). The main advantages of chalcogenide phase change memories are their direct write/overwrite capability, lower voltages of operation, large write/erase cycles, easiness to integrate with logic, etc. The phase change random access memories work on the principle of memory switching exhibited by chalcogenide glasses during which a local structural change (between amorphous and crystalline states) occurs due to an applied electric field. The development of newer phase change materials for NVRAM applications is based on synthesizing newer glass compositions and investigating their electrical switching characteristics by applying current/voltage pulses of different waveforms. The thermal studies on chalcogenide glasses which provide information about thermal stability, glass forming ability, etc., are also important while selecting a chalcogenide glass for PCM applications. The present thesis work deals with electrical switching and thermal studies on certain silicon based ternary telluride glasses (As-Te-Si, Ge-Te-Si and Al-Te-Si). The effect of network topological thresholds on the composition dependence of switching voltages and thermal parameters such as glass transition temperature, specific heat capacity, non-reversing enthalpy, etc., of these glasses has been investigated. The first chapter of the thesis provides an introduction to various properties of chalcogenide glasses, including their applications in phase change memories. The fundamental aspects of amorphous solids such as glass formation, glass transition, etc., are presented. Further, the concepts of rigidity percolation and self organization in glassy networks and the influence of local structural effects on the properties of glassy chalcogenides are discussed. Also, a brief history of evolution of phase change memories is presented. The second chapter deals with the experimental techniques employed in this thesis work; for sample preparation and for electrical switching studies, Alternating Differential Scanning Calorimetry (ADSC), Raman spectroscopy, NMR spectroscopy, etc. The third chapter discusses the electrical switching and thermal studies on As30Te70-xSix (2 ≤ x ≤ 22) and As40Te60-xSix (2 ≤ x ≤ 17) glasses. The composition dependence of electrical switching voltage (VT) and thermal parameters such as glass transition temperature (Tg), crystallization temperature (Tc), thermal stability (Tc-Tg), etc., reveals the occurrence of extended rigidity percolation and chemical thresholds in As30Te70-xSix and As40Te60-xSix glasses. Chapter 4 presents the electrical switching and thermal studies on Ge15Te85-xSix glasses (2 ≤ x ≤ 12). These glasses have been found to exhibit memory type electrical switching. While Ge15Te85-xSix glasses with x ≤ 5 exhibit a normal electrical switching, an unstable behavior is seen in the I-V characteristics of Ge15Te85-xSix glasses with x > 5 during the transition to ON state. Further, the switching voltage (VT) and initial resistance (R) are found to increase with addition of Si, exhibiting a change in slope at the rigidity percolation threshold of the Ge15Te85-xSix system. The ADSC studies on these glasses indicate the presence of an extended stiffness transition and a thermally reversing window in Ge15Te85-xSix in the composition range of 2 ≤ x ≤ 6. The fifth chapter deals with electrical switching investigations, thermal and structural studies on Al15Te85-xSix glasses (2 ≤ x ≤ 12). These glasses have been found to exhibit two crystallization reactions (Tc1 and Tc2) for compositions with x < 8 and a single stage crystallization is seen for compositions above x = 8. Also, a trough is seen in the composition dependence of non-reversing enthalpy (ΔHNR), based on which it is proposed that there is a thermally reversing window in Al15Te85-xSix glasses in the composition range 4 ≤ x ≤ 8. Further, Al15Te85-xSix glasses are found to exhibit a threshold type electrical switching at ON state currents less than 2 mA. The start and the end of the thermally reversing window seen in the thermal studies are exemplified by a kink and saturation in the composition dependence of switching voltages respectively. 27Al Solid State NMR measurements reveal that in Al15Te85-xSix glasses, Al atoms reside in 4-fold as well as 6-fold coordinated environments. Unlike in Al-As-Te glasses, there is no correlation seen between the composition dependence of the fraction of 4-fold and 6-fold coordinated aluminum atoms and the switching behavior of Al-Te-Si samples. Chapter 6 provides a comparison of the properties of the three glassy systems studied (As-Te-Si, Ge-Te-Si and Al-Te-Si), made to identify the system better suited for phase change memory applications. It is found that the Ge-Te-Si glassy system has better electrical/thermal properties for phase change memory applications. The seventh chapter describes easily reversible SET-RESET processes in Ge15Te83Si2 glass which is a promising candidate for phase change memory applications. This sample exhibits memory switching at a comparatively low threshold electric field (Eth) of 7.3 kV/cm. The SET and RESET processes have been achieved with 1 mA triangular current pulse for the SET process and 1 mA rectangle pulse (of 10 msec width) for RESET operation respectively. Further, a self-resetting effect is seen in this material upon excitation with a saw-tooth/square pulse. About 6.5x104 SET-RESET cycles have been achieved without any damage to the device. In chapter 8, results of in-situ Raman scattering studies on the structural changes occurring during the SET and RESET processes in Ge15Te83Si2 sample, are presented. It is found that the degree of disorder in the glass is reduced from OFF to SET state. The local structure of the sample under RESET condition is similar to that in the OFF state. The Raman results are found to be consistent with the switching results which indicate that the Ge15Te83Si2 glass can be SET and RESET easily. Further, Electron Microscopic studies on switched samples indicate the formation of nanometer sized particles of cSiTe2. A summary of the results obtained and the scope for future work are included in the chapter 9 of the thesis.

Microbeam radiation therapy (MRT) is an experimental form of radiation treatment which causes less damage to normal tissue in comparison with customary broad-beam radiation treatment. In this method the synchrotron generated X-ray beam is passed through a multislit collimator and applied to the tumor in the form of an array of planar microbeams. MRT dosimetry is an extremely challenging task and no current detector can provide the required wide dynamic rang and high spatial resolution. In this thesis, fluorophosphate (FP) and fluoroaluminate (FA) glass plates doped with trivalent samarium (Sm3+) are characterized towards developing a potential X-ray detector suitable for MRT dosimetry. The detection is based on the difference in the photoluminescence signatures of Sm3+ ions and Sm2+ ions; the latter are formed under X-ray irradiation. This valency conversion is accompanied by the formation of defects including hole centers (HCs) and electron centers (ECs) in the glass structure which absorb light in the UV and visible regions (induced absorbance). Both FP and FA glasses show promising dynamic range for MRT and may be used as a linear sensor up to ~150 Gy and as a nonlinear sensor up to ∼2400 Gy, where saturation is reached. X-ray induced defects saturate at the same dose. The optimum doping concentration is in the 0.001˗ 0.2 at.% range. Doping with higher concentrations will decrease the conversion efficiency. The glass plates also show a very promising spatial resolution (as high as a few microns) for recording the dose profile of microbeams which is readout using a confocal fluorescence microscopy technique. These plates are restorable as well and the response is reproducible. The effects of previous X-ray exposure including samarium valency conversion as well as induced absorbance may be erased by annealing at temperatures exceeding the glass transition temperature Tg while annealing at TA < Tg enhances the response. This enhancement is explained by a thermally stimulated relaxation of host glass ionic matrix surrounding X-ray induced Sm2+ ions. Optical erasure is another practical means to erase the recorded data. Nearly complete Sm2+ to Sm3+ reconversion (erasure) is achieved by intense optical illumination at 405 nm. While, existing X-ray induced bands would be only partially erased. Electron spin resonance (ESR) and optical absorbance spectroscopy are used to investigate the nature of X-ray induced defects and their correlation with Sm valency conversion. A model based on competition between defect center formation and the Sm3+ ⇆ Sm2+ conversion successfully explains the different processes occurring in the glass matrix under X-ray irradiation.

During the last few years the scientific interest in chalcogenides glasses has been provoked on account of their properties and new application possibilities. These materials exhibit electrical and optical properties, which make them useful for several potential applications. Specifically the threshold and memory switching behavior and the infrared transmission of many of these glasses make the materials to be well suitable for use in memory devices and in fiber optics. Multicomponent glasses have been found to be more useful for many of these applications since the properties could be tailored for the specific uses. On account of this there has been great deal of interest in recent years in understanding the composition dependent variations of physical properties in these glasses. Models based on network topology and chemical ordering have been proposed to explain the composition dependence of physical properties. The Chemically Ordered Covalent Network (COCN) model is one of the best efforts put forth in this subject. This model predicts distinctive physical properties of these glasses for compositions at which there is a maximum number of heteropolar bonds. A physical model based on changes in network topology with composition has been proposed recently. This model predicts the rigidity to percolate in the network at the mean coordination number = 2.40. This critical value of at which the rigidity percolates is called the mechanical threshold or the rigidity percolation threshold. One more argument based on medium range interactions, existing in these glassy networks, suggests that the mechanical threshold should occur at = 2.67. A general lack of consensus in the existing experimental reports on the mechanical threshold in some chalcogenides glasses prevents one from identifying the correct threshold value of . A systematic study of the composition dependence of glasses with a large glass-forming region is necessary to resolve this controversy. The correct threshold value of and the reason for the departure from this value in the other cases is the first step towards verifying the applicability of this model to chalcogenide glasses. Glasses belonging to IV — V — VI groups are natural candidates for this study because of their large glass forming region. It also seems possible to isolate the chemical threshold from interfering with the mechanical threshold in some of these glasses. In device applications of any semiconductor the optical and the electrical band gaps need to be varied and this is commonly done by doping. The large density of valence alteration pairs and intrinsic disorder of amorphous semiconductors counter-balances the effects of external additives. As a result, it is hard to electrically dope these materials. Non-equilibrium experimental techniques have been used to some extent, but one of the limitations is that they are confined to the thin film state. The finding that p to n type conduction sign changes can be induced by Bi and Pb in bulk Ge-M (M= S, Se and Te) glasses has therefore created special interest. This thesis deals with Ge-Se glass matrix doped with Te, Bi and Pb. The optical, thermal and electrical properties have been studied. The present thesis work is arranged in several chapters. The basic introduction of chalcogenide glasses is given in chapter one. This includes an introduction to chalcogenide glasses followed by a brief discussion on the important structural models, the possible defects in chalcogenide glasses and the electrical, optical and thermal properties of chalcogenide glasses. The second chapter discusses the experimental techniques used in the present investigations. The basic principles and theory behind the experiments, the experimental setup and the experimental procedure leading to the determination of the physical properties are given here. These include information about Differential Scanning Calorimetry (DSC), Photo acoustic (PA) spectroscopy and Photoluminescence studies. In the third chapter the experimental investigations on Ge-Se-Te glasses are presented. The chapter starts with the preparation and characterization of these glasses. It then gives an account of the earlier studies on Ge-Se-Te glasses that are relevant to the present work. The results of the DSC and PA studies are discussed in the following two sections. In the systems with Gex Se80-x Te20 and Gex Se75.x Te25, glasses with less than 20 at. % of Ge do not show any crystallization peak due to Se rich content. But Te and Ge-rich glasses show strong crystallization tendency. The composition dependence of Tg of this glassy system gives an evidence for the occurrence of the topological threshold or mechanical threshold at = 2.40 and chemical threshold at = 2.67. These can be explained on the basis of COCN model. The optical band gap and thermal diffusivity studies also show anomalous behavior at = 2.40 and = 2.67. The experimental results on Ge-Se-Te glasses are summarized in the last section of this chapter. The investigations on Bi doped Ge-Se and Ge-Se-Te glasses are given in the fourth chapter. The chapter starts with a brief introduction of preparation, characterization and a short review of earlier work. In PA studies the anomalous behavior is observed in thermal diffusivity and thermal diffusion length plot at 8-9 at. % of Bi doping of the Ge-Se and Ge-Se-Te glasses where the conduction changes from p to n type. These results are explained on the basis of percolation model and the formation of Bi2Se3 microcrystalline phase. Finally these results are summarized at the end of the chapter. The fifth chapter is devoted to the investigations on Pb doped Ge-Se glasses. It is arranged in five sections; preparation and characterization, earlier work, Photo acoustic and Photoluminescence studies. In PA studies the composition dependence of thermal diffusivity show anomalous behavior at x =F 9 at % of Pb in Pbx Ge42-x Sesg glasses and y = 21 at. % of Ge in Pb2o Gey Seso-y glasses where the conduction changes from p to n type. After that it reaches the maximum. After the conduction sign changes the conductivity increases with addition of respective Pb and Ge concentration in both series of glasses, which is reflected in thermal diffusivity value also. The results have been explained on the basis of COCN model. From PL studies, the PL intensity is high in un-doped Ge42 Scss glasses. With the addition of Pb into Ge-Se system the PL intensity goes down drastically up to 9 at. % of Pb, beyond 9 at. % the PL intensity is approximately the same up to 15 at. %. In the last section the results are summarized. Chapter six summarizes the essential features of the work reported in the thesis. These conclusions are drawn from the present and the earlier reported studies on Ge-Se-Te glasses, Bi doped Ge-Se and Ge-Se-Te glasses and Pb doped Ge-Se glasses. Finally based on the present experimental results, some future work has been suggested which could throw some light on a better understanding of/? to n transition and defects state of these glasses. It is worth extending the microscopic phase separation studies in these glasses. Highly sensitive experimental techniques are needed in this regard. Also some simulation work like Monte-Carlo simulation and Molecular dynamics simulation needs to be undertaken for understanding the microscopic phase separation and the role of defects in carrier type reversal in these glassy materials. All the references cited in the thesis are collected and listed at the end of the thesis.

碩士
義守大學
材料科學與工程學系
102
Since the development of amorphous alloys, most scholars using Au, Pd and other more expensive metal elements as the substrate. In order to reduce costs and improve usability, scholars began to develop the Cu-based amorphous alloys, with lower cost and good mechanical properties, especially for Cu-Zr-based amorphous alloy with a deep eutectic point in Cu50Zr50 alloy system, it can easily formed an amorphous alloy in the low temperature. Therefore, Cu50Zr43Al7 alloy with high glass forming ability were be used at the base alloy in this experiment. Replace Cu elements by Ag element. Pure Ag element are selected to partially substitute Cu element to form Cu50-xZr43Al7Agx (x=0, 3, 4, 5, 6) bulk metallic glasses (BMGs) in this research. According to the literature, the adding of Ag elements can effectively enhance the thermal properties and the mechanical properties of amorphous alloys. The BMG specimens were be prepared by the use of arc-melting and injection casting process. The effect of Ag addition on the vitrification, thermal and mechanical properties of Cu-Zr-Al-Ag amorphous alloys were studied here. BMG specimens were examined by X-ray diffractometer (XRD), differential scanning calorimeter (DSC), Vickers hardness tester, material test system (MTS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results revealed that the Cu50-xZr43Al7Agx alloy systems were formed in amorphous state in this study. The glass transition temperature (Tg) and the liquidus temperature (Tl) of Cu-Zr-Al alloy decreased with adding of Ag. Hence the supercooled liquid region (Tx) and  (=Tx/(Tg+Tl)) Cu45Zr43Al7Ag5 alloy increased to 76K and 0.425, respectively. It means that the enhancement of the thermal stability and glass forming ability of Cu-Zr-Al-Ag BMG alloys with adding of Ag. The result of room temperature compressive fracture strength and strain measured from Cu47Zr43Al7Ag3 was of about 2191 MPa and 2.0%. Dense dispersion of vein pattern on the fracture surface of Cu47Zr43Al7Ag3 BMG specimen via compressive test was be observed, indicating a typical ductile fracture behavior and the improved of plasticity of alloys with minor addition of Ag. In the Cu47Zr43Al7Ag3 alloy, there were 4~10 nm nanocrystalline phase uniformly distributed in the substrate. This is the reason that the strength and plastic strain of the alloy to be enhanced here.

Chalcogenide glass based Phase Change Memories (PCMs) are being considered recently as promising alternatives to conventional non-volatile Random Access Memories (NVRAMs). PCMs offer high performance & low power consumption, in addition to other advantages, such as high scalability, high endurance and compatibility with complementary metal oxide semiconductors (CMOS) technologies. Basically PCM is a resistance variable non-volatile memory in which the memory bit state is defined by the resistance of the material. In this case, the initial ‘OFF’ state (logic zero) corresponds to the high resistance amorphous state and the logic 1 or ‘ON’ state corresponds to low resistance crystalline state. The present thesis work deals with electrical, thermal, mechanical and optical characterization of certain tellurium based chalcogenide glasses in bulk and thin film form for phase change memory applications. A comparative study has been done on the electrical switching behavior of Ge-Te-Se & Ge-Te-Si amorphous thin film samples with their bulk counterparts. Further, electrical switching and thermal studies have been undertaken on bulk Ge-Te-Bi and Ge-Te-Sn series of samples. The composition dependence of switching voltages of bulk and thin film samples studied has been explained on the basis of different factors responsible for electrical switching. The thesis contains ten chapters: Chapter 1 deals with a brief introduction on chalcogenides and their applicability in phase change memories. The glass transition phenomenon, synthesis of chalcogenide alloys, different structural models of amorphous semiconductors and electrical switching behavior are also discussed in detail in this chapter. Further, a brief description of optical and mechanical properties along with the principles of few characterization techniques used is discussed. Also, a brief overview on PCM application of chalcogenides is presented. The second chapter provides the details of various experimental techniques used to measure electrical, thermal, optical and mechanical properties of few tellurium based chalcogenide glassy systems. In the third chapter, the electrical switching behavior of amorphous Al23Te77 thin film devices, deposited in co-planar geometry, has been discussed. It is found that these samples exhibit memory type electrical switching. Scanning Electron Microscopic studies show the formation of a crystalline filament in the electrode region which is responsible for switching of the device from high resistance OFF state to low resistance ON state. The switching behavior of thin film Al-Te samples is found to be similar to that of bulk samples, with the threshold fields of bulk samples being higher. This has been understood on the basis of higher thermal conductance in bulk, which reduces the Joule heating and temperature rise in the electrode region. Electrical switching and thermal behavior of bulk; melt quenched Ge18Te82-xBix glasses (1 ≤ x ≤ 4) are presented in chapter 4. Ge-Te-Bi glasses have been found to exhibit memory type electrical switching behavior, which is in agreement with the lower thermal diffusivity values of these samples. A linear variation in switching voltages (also known as threshold voltages) (Vt) has been found with increase in thickness. The switching voltages have been found to decrease with an increase in temperature which is due to the decrease in the activation energy for crystallization at higher temperatures. Further, Vt of Ge18Te82-xBix glasses have been found to decrease with the increase in Bi content, indicating that in the Ge-Te-Bi system, the resistivity of the additive has a stronger role to play in the composition dependence of Vt, in comparison with the network connectivity and rigidity factors. In addition, the composition dependence of crystallization activation energy has been found to show a decrease with an increase in Bi content. X-ray diffraction studies on thermally crystallized samples reveal the presence of hexagonal Te, GeTe and Bi2Te3 phases. The fifth chapter deals with the electrical switching studies and optical band gap measurements on GexSe35-xTe65 (17 ≤ x ≤ 23) amorphous thin film samples. These thin film samples coated with sandwich geometry are found to switch with very low voltages as compared to bulk samples of the same chalcogenide glasses. The switching voltages and optical band gap are found to increase with the addition of Ge at the expense of Se. High structural cross linking with progressive addition of 4-fold coordinated Ge atoms could be the one of the reasons of increasing switching voltage and stronger Ge-Se bond strength could be the reason of increasing band gap for these chalcogenide glasses. In chapter 6, electrical switching studies on amorphous Ge15Te85-xSix (1 ≤ x ≤ 6) thin film samples have been described and the results are compared with their bulk counterparts. Similar trend has been found for both bulk and film samples when the threshold field is varied with composition. Optical band gap has been measured as a function of composition for these films, which also shows a behavior similar to that of switching voltages. The increasing trend in the variation with composition of electrical switching voltages and optical band gap are due to the increase in network connectivity and rigidity as Si atoms are incorporated into the Ge-Te system. Chapter 7 summarizes the electrical switching and glass forming ability of the Ge-Te-Sn glasses of two different composition tie-lines, namely Ge15Te85-xSnx and Ge17Te83-xSnx. Glasses belonging to both the series have been found to exhibit memory type of electrical switching behavior. The thickness dependence of threshold voltages is also found to support the memory switching behavior of the system. Further, ADSC studies are undertaken to explore the thermal behavior of these glasses which indicates that the crystallization tendency increases as Sn concentration is increased in the Ge-Te network. XRD studies done on two samples from both the series, reveal the fact that Sn atoms do not take part actively to enhance the network connectivity and rigidity. The composition dependence of crystallization temperature, metallicity factor and results of XRD studies are put together to explain the variation with composition of threshold voltages for both the series of samples. In chapter 8, investigations on the electrical switching behavior of Ge15Te85-xSnx (1 ≤ x ≤ 5) and Ge17Te83-xSnx (1 ≤ x ≤ 4) amorphous thin films have been discussed. Both the series of samples have been found to exhibit memory type of electrical switching behavior. The composition dependence of threshold voltage shows a decreasing trend, which has been explained on the basis of the Chemically Ordered Network (CON) model, bond strength and the metallicity factor. The optical band gap variation of both the series also exhibits a similar decreasing trend with composition. The observed behavior has been understood on the basis of higher atomic radius of Sn atom than Ge atom, which makes the energy difference between bonding and anti bonding state less at band edge. Chapter 9 deals with the nano-indentation studies on Ge15Te85-xSix (0 ≤ x ≤ 9) bulk glasses. The composition dependence of young’s modulus and hardness is studied systematically in this glassy system. The density of the samples of different compositions has also been measured, which strongly supports the variation of Young’s Modulus and hardness with composition. The composition dependence of mechanical properties of Ge-Te-Si samples has been understood on the basis of the presence of an intermediate phase and a thermally reversing window in this glassy system. A summary of the significant results obtained in the present thesis work is presented in the last chapter along with the scope for future work.

Ceramics and polymer-ceramic composites associated with high dielectric constants are of both scientific and industrial interest as these could be used in devices such as capacitors, resonators and filters. High dielectric constant facilitates smaller capacitive components, thus offering the opportunity to miniaturize the electronic devices. Hence there is a continued interest on high dielectric constant materials over a wide range of temperatures. Recently, CaCu3Ti4O12 (CCTO) ceramic which has centro-symmetric body centered cubic structure has attracted considerable attention due to its large dielectric constant (ε ~104-105) which is nearly independent of frequency (upto 10 MHz) and low thermal coefficient of permittivity (TCK) over 100-600K temperature range. Apart from the high dielectric ceramics, high dielectric polymer-ceramic composites have also become promising materials for capacitor applications. By combining the advantages of high dielectric ceramics and low leakage behaviour of polymers, one can fabricate new hybrid materials with high dielectric constants, and high breakdown field to achieve high volume efficiency and energy storage density for capacitor applications. The CCTO polycrystalline powders were generally prepared by the conventional solid-solid reaction route with CaCO3, TiO2 and CuO as the starting materials. This method of preparation often requires high temperatures and longer durations. To overcome these difficulties, in the present investigations, an attempt has been made to synthesize CCTO by adopting microwave assisted heating technique and wet chemical synthesis routes. Also the CCTO crystallites (size varying from nano to micrometers) incorporated in the Polyvinyliden fluoride (PVDF) and Polyaniline (PANI) matrix and several composites with high dielectric constants were fabricated and investigated. Further, the high dielectric constant glasses in the system (100-x)TeO2-xCaCu3Ti4O12, (x=0.5 to 3) were fabricated by the conventional melt-quenching technique and their structural and dielectric properties were studied. The results obtained pertaining to these aforementioned investigations are classified as follows. Chapter 1 is intended to give basic information pertaining to the dielectrics and various mechanisms associated with high dielectric constants. Brief exposure to the high dielectric constant materials is also given. The structural aspects of CCTO, various synthetic routes adopted for the synthesis and the origin of the dielectric anomaly in CCTO are elaborated. In addition, basic information about the high dielectric polymer-ceramic composites and glasses are provided. In chapter 2 the various experimental techniques that were employed to synthesize and characterize the materials under investigation were discussed. Chapter 3 reports the synthesis and characterization of CaCu3Ti4O12, (CCTO) powders by microwave assisted heating at 2.45 GHz, 1.1kW. The processing and sintering were carried out at different temperatures for varied durations. The optimum calcination temperature using microwave heating was found to be 950oC for 20 minutes to obtain cubic CCTO powders. This is found to be fast and energy efficient as compared to that of the conventional methods. The structure, morphology and dielectric properties of the CCTO ceramic processed by microwave assisted heating were studied via X-ray diffraction, Scanning electron microscopy (SEM) and impedance analyser. These studies revealed that, the microwave sintered (MS) samples were less porous than that of the conventional ones. Relative density of about 95% was achieved for the MS pellets (1000oC/60min) while for the conventional sintered (CS) pellets (1100oC/2h) it was only 91%. The dielectric constants for the microwave sintered (1000oC/60min) ceramics were found to vary from 11000 to 6950 in the 100 Hz to 100 kHz frequency range. The presence of larger grains (6-10μm) in the MS samples contributed to the higher dielectric constants. Chapter 4 deals with the synthesis of complex oxalate precursor, CaCu3(TiO)4(C2O4)8 • 9H2O, by the wet chemical route. The various trials and the different reaction schemes involved for the preparation of complex oxalate precursor were highlighted. The oxalate precipitate thus obtained was characterized by the wet chemical analyses, X-ray diffraction, FTIR absorption and TG/DTA analyses. The complex oxalate precursor, CaCu3(TiO)4(C2O4 )8.9H2O was subjected to thermal oxidative decomposition and the products of thermal decomposition were investigated employing XRD,TGA, DTA and FTIR techniques. Nanocrystallites of CaCu3Ti4O12 with the size varying from 30-200 nm were obtained at a temperature as low as 680oC. The nanocrystallites of CaCu3Ti4O12 were characterized using Electron Spin Resonance (ESR) and optical reflectance techniques. The selected area electron diffraction (SAED) pattern with the zone axis [012] and spot pattern in electron diffraction (ED) indicate their single-crystalline nature. The optical reflectance and ESR spectra indicate that the Cu (II) coordination changes from distorted octahedra to nearly flattened tetrahedra (squashed) to square planar geometry with increasing heat treatment temperature. The powders derived from the oxalate precursor have excellent sinterability resulting in high density ceramics which exhibited giant dielectric constants upto 40,000 (1 kHz) at 25oC, accompanied by low dielectric loss < 0.07. The effect of calcium content on the dielectric properties of CaxCu3Ti4O12 (x=0.90, 0.97, 1.0, 1.1 and 1.15) derived from the oxalate route was described in Chapter 5. The structural, morphological and dielectric properties of the ceramics were studied using X-ray diffraction, Scanning Electron Microscope along with Energy Dispersive X-ray Analysis (EDX), and Impedance analyzer. The X-ray diffraction patterns obtained for the x= 0.97, 1.0 and 1.1 ceramics could be indexed to a body– centered cubic perovskite related structure associated with the space group Im3. The microstructural studies revealed that the grains are surrounded by exfoliated sheets of Cu-rich phase. The microstructure that is evolved for the Ca0.97 ceramic more or less resembles that of the Ca1.0 ceramic, but the density of such exfoliated sheets of cu-rich phase is lesser for the Ca0.97 ceramic and none for Ca1.1 ceramic. The sintered pellet (x=0.97) was ground and thinned to the required thickness (~ 20nm) and analyzed using Transmission Electron Microscopy (TEM). The current-voltage (I-V) characteristics of the ceramics exhibited non-linear behaviour. The dielectric properties of these suggest that the sample corresponding to the composition x=0.97, has a reduced dielectric loss while retaining its high dielectric constant. Chapter 6 illustrates the results concerning the fabrication and characterization of nanocrystal composites of Polyaniline (PANI) and CaCu3Ti4O12 (CCTO). These were prepared using a simple procedure involving in-situ polymerization of aniline in dil. HCl. The PANI and the PANI-CCTO composites were subjected to X-ray diffraction, Fourier Transform Infrared (FTIR), Thermo gravimetric, Scanning Electron Microscopic (SEM) and Transmission electron microscopic analyses. The FTIR spectra recorded for the composites was similar to that of pure PANI unlike in the case of X-ray diffraction wherein the characteristics of both PANI and CCTO were reflected. The TGA in essence indicated the composites to have better thermal stability than that of pure PANI. The composite corresponding to 50%CCTO-50%PANI exhibited higher dielectric constant (4.6x106 @100Hz). The presence of the nano crystallites of CCTO embedded in the nanofibers of PANI matrix was established by TEM. The AC conductivity increased slightly upto 2kHz as the CCTO content increased in the PANI which was attributed to the polarization of the charge carriers. The value of dielectric constant obtained was higher than that of the other PANI based composites reported in the literature. Chapter 7 deals with the fabrication and characterization of diphasic Poly(vinylidene fluoride) (PVDF)-CCTO composite. The CCTO crystallites (size varying from nano to micrometers) incorporated in the Polyvinylidene fluoride (PVDF) and composites with varying CCTO content were fabricated. The structural, morphological and dielectric properties of the composites were studied using X-ray diffraction, Thermal analysis, Scanning Electron Microscope (SEM), Transmission Electron Microscopic (TEM) and Impedance analyzer. The room temperature dielectric constant as high as 95 at 100Hz has been realized for the composite with 0.55 Vol.fraction of CCTO (micro sized crystallites), which has increased to about 190 at 150oC. Whereas, the PVDF/CCTO nanocrystal composite with 0.13Vol.fraction of CCTO has exhibited higher room temperature dielectric constant (90 at 100Hz). The PVDF/CCTO nanocrystal composite was further investigated for the breakdown strength and electric modulus. The breakdown strength plotted against the dielectric constant evidenced an inverse relationship of breakdown voltage with the dielectric constant. The relaxation processes associated with these composites were attributed to the interfacial polarization or Maxwell-Wagner-Sillars (MWS) effect. Various theoretical models were employed to rationalize the dielectric behavior of these composites. The fabrication and characterization details of optically clear colored glasses in the system (100-x)TeO2-xCaCu3Ti4O12, (x=0.5 to 3 mol%) are reported in Chapter 8. The color varies from olive green to brown as the CaCu3Ti4O12 (CCTO) content increased in TeO2 matrix. The X-ray powder diffraction and differential scanning calorimetric analyses that were carried out on the as-quenched samples confirmed their amorphous and glassy nature respectively. The optical transmittance of the glasses exhibited typical band-pass filter characteristics. The dielectric constant and loss in the 100 Hz-1MHz frequency range were monitored as a function of temperature (323K673K). The dielectric constant and the loss increased as the CCTO content increased in TeO2 at all the frequencies and temperatures under study. Further, the dielectric constant and the loss were found to be frequency independent in the 323-473 K temperature range. The value obtained for the loss at 1MHz was 0.0019 which was typical of low loss materials, and exhibited near constant loss (NCL) contribution to the ac conductivity in the 100Hz-1MHz frequency range. The electrical relaxation was rationalized using the electrical modulus formalism. These glasses are found to be more stable (a feature which may be of considerable interest) as substrates for high frequency circuit elements in conventional semiconductor industries. Thesis ends with summary and conclusions, though each chapter is provided with conclusions and complete list of references.

博士
輔仁大學
應用科學與工程研究所博士班
98
Fluorides are present used to accomplish optical coatings for UV and deep UV range applications. Many techniques such as thermal evaporation, ion beam sputtering, electron-beam evaporation, magnetron sputtering, and ion-assisted deposition (IAD) are applied to improve the quality of fluoride films. Nevertheless, improvements of their optical and microstructural qualities are still needed. In this study, fluoride films as magnesium fluoride (MgF2), gadolinium fluoride (GdF3) and aluminum fluoride (AlF3) were fabricated at room temperature by using a thermal evaporation method with an ion-assisted deposition technique. Using sulfur hexafluoride (SF6) as a working gas in the IAD process so that more F- ions can be created from the dissociation of SF6 gas to improve the stoichiometry of fluoride films. Furthermore, optical and microstructural properties of the films deposited by using different working gases such as argon (Ar), oxygen mixed sulfur hexafluoride (O2+SF6) and without using gas in the IAD process or using SF6 as an ambient gas to where investigated. In this study, the optimal ion-assisted voltage and current in the IAD process were determined first. The optical properties of the films were analyzed by UV/Visible/NIR spectrophotometer, micro-spot spectroscopic ellipsometer and Fourier transform infrared spectrometer (FTIR). The microstructural properties of the films were examined by atomic force microscope (AFM), field emission scanning electron microscope (FE-SEM) and X-ray diffractometer (XRD). Moreover, X-ray photoelectron spectroscopy (XPS) was used to investigate the composition, atomic concentrations and stoichiometry of fluoride films. The binding energy (BE) shifts of Mg 2p, Gd 4d, Al 2p, O 1s and F 1s were analyzed after spectra were decomposed by some sub-peaks using a peak fitting software. The contaminants in the fluoride films such as Ar and S atoms were also identified by XPS. The correlations among the film composition, optical properties and physical properties were also discussed. In conclusion, it was found that SF6 used as a working gas in the thermal evaporation process with an IAD technique, three fluoride films, MgF2, GdF3 and AlF3, all showed better optical qualities, packing densities and stoichiometric structures.

Chalcogenide glasses have attracted considerable attention due to their infrared transparency, low phonon energy, and high non linear optical properties. They have been explored as promising candidate for optical memories, gratings, switching devices etc. Because of their low phonon energy and high refractive indices, now a days these are used for high efficiency fibre amplifiers. Nevertheless, the availability of amorphous semiconductors in the form of high quality multilayers provides potential applications in the field of micro and optoelectronics. Among amorphous multilayers, chalcogenide multilayers are attractive because of the prominent photoinduced effects. Studies in chalcogenide amorphous multilayer have been directed towards two phenomena. One is photoinduced interdiffusion in short period multilayer systems which finds potential applications in holographic recording and fabrication of phase gratings . The other is photo darkening or photobleaching which is also known in thick films. These multilayers exhibit prominent photoinduced effects, similar to those exhibited by uniform thin films. In spite of its practical usefulness, the mechanism of photoinduced interdiffusion is not properly understood. Since most structural transformations are related to atomic diffusion, understanding of the structural transformation must be based on the diffusion process. The main aim of this thesis is to study the photoinduced diffusion in Sb/As2S3 multilayered films and (As2S3)1-xSbx thin films. In literature, there are reports about the photoinduced interdiffusion in Se/As2S3 and Bi/As2S3 multilayered films, but the mechanisms of photoinduced interdiffusion of these elements are not very clear. Raman scattering and infrared spectroscopy techniques have been used to study the photoinduced interdiffusion in Se/As2S3 and Bi/As2S3 multilayered films by Malyovanik et al. (M. Malyovanik, M. Shiplyak, V. Cheresnya, T. Remeta, S. Ivan, and A. Kikineshi, J. Optoelectron. Adv. Mater. 5, 397 (2003). But many questions remain unanswered. The characteristic spectra of components in the multilayer and those of the diffused layer were rather similar. In the present thesis, photoinduced interdiffusion in Sb/As2S3 multilayered samples are studied by Fourier Transform Infrared spectroscopy (FTIR) at room and low temperature and X-ray photoelectron spectroscopy (XPS). The photoinduced effects in (As2S3)1-xSbx thin films are studied by FTIR, XPS and Raman Spectroscopy. The detailed information about the distribution of electronic states in the absorption edge, localized states and the new bonds formed between the components due to photoinduced interdiffusion elucidated from the above studies will give more insight into the mechanism and kinetics of photoinduced interdiffusion. The thesis consists of seven chapters. References are given at the end of each chapter.