Дисертації з теми "Structural-phase transformations"
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1
Cao, Hu. "Phase transformations in highly electrostrictive and magnetostrictive crystals: structural heterogeneity and history dependent phase stability." Diss., Virginia Tech, 2008. http://hdl.handle.net/10919/28549.
Повний текст джерелаАнотація:
Ferroelectric and ferromagnetic materials have been extensively studied for potential applications in sensors, actuators and transducers. Highly electrostrictive (1-x)Pb(Mg1/3Nb2/3)-xPbTiO₃ (PMN-xPT) and highly magnetostrictive Fe-xat.%Ga are two such novel materials. Both materials systems have chemical disorders and structural inhomogeneity on a microscale, giving rise to an interesting diversity of crystal structures and novel macroscopic physical properties, which are dependent on thermal and electrical histories of the crystals. In this thesis, I have to investigated phase transformations in these two systems under thermal and field (electric/magnetic) histories, using x-ray and neutron scattering techniques.
In PMN-xPT crystals, x-ray and neutron diffractions were performed along the different crystallographic orientations and for different thermal and electrical histories. Various intermediate monoclinic (M) phases that structurally “bridge” the rhombohedral (R) and tetragonal (T) ones across a morphtropic phase boundary (MPB) have been observed. Systematic investigations of (001) and (110) electric (E) field-temperature phase diagrams of PMN-xPT crystals have demonstrated that the phase stability of PMN-xPT crystals is quite fragile: depending not only on modest changes in E (≤ 0.5kV/cm), but also on the direction along which E is applied. Structurally bridging monoclinic Mc or orthorhombic (O) phases were found to be associated with the T phase, whereas the monoclinic Ma or Mb phases bridged the Cubic (C) and R ones.
In addition, neutron inelastic scattering was performed on PMN-0.32PT to study the dynamic origin of the MPB. Data were obtained between 100 and 600 K under various E applied along the cubic [001] direction. The lowest frequency zone-center, transverse optic phonon was strongly damped and softened over a wide temperature range, but started to recover on cooling into the T phase at the Curie temperature (TC). Comparisons of my findings with prior ones for PMN and PMN-0.60PT suggest that the temperature dependence and energy scales of the soft mode dynamics in PMN-xPT are independent of PT concentration below the MPB, and that the MPB may be defined in composition space x when TC matches the temperature at which the soft mode frequency begins to recover. High-resolution x-ray studies then showed that the C–T phase boundary shifted to higher temperatures under E by an expected amount within the MPB region: suggesting an unusual instability within the apparently cubic phase at the MPB.
In Fe-xat.%Ga alloys, the addition of Ga atoms into the b.c.c. α-Fe phase also results in diversity of crystal structures and structural inhomogeneity, which are likely the source of its unusual magneto-elastic properties. I have carefully investigated decomposition of Fe-xat.%Ga alloys subjected to different thermal treatments by x-ray and neutron diffraction for 12 < x < 25. Quenching was found to suppress the formation of a DO₃ structure in favor of a high-temperature disordered bcc (A2) one. By contrast, annealing produced a two-phase mixture of A2 + DO₃ for 14 < x < 20 and a fully DO₃ phase for x = 25. A splitting of the (2 0 0) and (0 0 2) Bragg peaks observed along the respective transverse directions indicated that Fe-xat.%Ga –crystals' are composed of several crystal grain orientations (or texture structures), which are slightly tilted with respect to each other. In order to investigate the local structural distortions and heterogeneities, neutron diffuse scattering was performed on Fe-x%Ga alloys for different thermal conditions. Diffuse scattering around a (100) superlattice reflection was found for 14 < x < 22 in the furnace-cooled condition, indicative of short-range ordered DO₃ nanoprecipitates in an A2 matrix. This diffuse intensity had an asymmetric radial contour and an off-centering. Analysis (x=19) revealed two broad peaks with c/a–1.2: indicating that the DO₃-like nanoprecipitates are not cubic, but rather of lower symmetry with a large elastic strain. The strongest diffuse scattering was observed for x=19, which correspondingly had maximum magnetostriction: indicating a structural origin for enhanced magnetostriction.Ph. D.
2
Chapman, Brandon D. "The role of disorder in structural phase transitions in perovskite ferroelectrics /." Thesis, Connect to this title online; UW restricted, 2003. http://hdl.handle.net/1773/9692.
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3
Banerjee, Rajarshi. "Structural and phase transformations in sputter deposited titanium-aluminum multilayered and alloy thin films /." The Ohio State University, 1997. http://rave.ohiolink.edu/etdc/view?acc_num=osu148794790840253.
Повний текст джерела
4
Matychak, Yaroslav, Viktor Fedirko, Iryna Pohrelyuk, and Oleh Tkachuk. "Modeling of diffusion saturation of titanium by nitrogen taking into consideration structural and phase transformations." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-190082.
Повний текст джерела
5
Matychak, Yaroslav, Viktor Fedirko, Iryna Pohrelyuk, and Oleh Tkachuk. "Modeling of diffusion saturation of titanium by nitrogen taking into consideration structural and phase transformations." Diffusion fundamentals 11 (2009) 48, S. 1-2, 2009. https://ul.qucosa.de/id/qucosa%3A14011.
Повний текст джерела
6
Sun, Xinxing. "Phase Transformations and Switching of Chalcogenide Phase-change Material Films Prepared by Pulsed Laser Deposition." Doctoral thesis, Universitätsbibliothek Leipzig, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-224762.
Повний текст джерелаАнотація:
The thesis deals with the preparation, characterization and, in particular, with the switching properties of phase-change material (PCM) thin films. The films were deposited using the Pulsed Laser Deposition (PLD) technique. Phase transformations in these films were triggered by means of thermal annealing, laser pulses, and electrical pulses. The five major physical aspects structure transformation, crystallization kinetics, topography, optical properties, and electrical properties have been investigated using XRD, TEM, SEM, AFM, DSC, UV-Vis spectroscopy, a custom-made nanosecond UV laser pump-probe system, in situ resistance measurements, and conductive-AFM.
The systematic investigation of the ex situ thermally induced crystallization process of pure stoichiometric GeTe films and O-incorporating GeTe films provides detailed information on structure transformation, topography, crystallization kinetics, optical reflectivity and electrical resistivity. The results reveal a significant improvement of the thermal stability in PCM application for data storage. With the aim of reducing the switching energy consumption and to enhance the optical reflectivity contrast by improving the quality of the produced films, the growth of the GeTe films with simultaneous in situ thermal treatment was investigated with respect to optimizing the film growth conditions, e.g. growth temperature, substrate type.
For the investigation of the fast phase transformation process, GeTe films were irradiated by ns UV laser pulses, tailoring various parameters such as pulse number, laser fluence, pulse repetition rate, and film thickness. Additionally, the investigation focused on the comparison of crystallization of GST thin films induced by either nano- or femtosecond single laser pulse irradiation, used to attain a high data transfer rate and to improve the understanding of the mechanisms of fast phase transformation.
Non-volatile optical multilevel switching in GeTe phase-change films was identified to be feasible and accurately controllable at a timescale of nanoseconds, which is promising for high speed and high storage density of optical memory devices. Moreover, correlating the dynamics of the optical switching process and the structural information demonstrated not only exactly how fast phase change processes take place, but also, importantly, allowed the determination of the rapid kinetics of phase transformation on the microscopic scale.
In the next step, a new general concept for the combination of PCRAM and ReRAM was developed. Bipolar electrical switching of PCM memory cells at the nanoscale can be achieved and improvements of the performance in terms of RESET/SET operation voltage, On/Off resistance ratio and cycling endurance are demonstrated. The original underlying mechanism was verified by the Poole-Frenkel conduction model. The polarity-dependent resistance switching processes can be visualized simultaneously by topography and current images. The local microstructure on the nanoscale of such memory cells and the corresponding local chemical composition were correlated.
The gained results contribute to meeting the key challenges of the current understanding and of the development of PCMs for data storage applications, covering thin film preparation, thermal stability, signal-to-noise ratio, switching energy, data transfer rate, storage density, and scalability.
7
ROCHA, RENATA A. "Preparação e caracterização de compostos com matriz de LAMOX." reponame:Repositório Institucional do IPEN, 2005. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11292.
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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
FAPESP:01/12269-7
8
Sikorski, Pawel Tadeusz. "Crystallisation and structural studies of monodisperse nylon oligomers and related polymers." Thesis, University of Bristol, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.391096.
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Leng, Siwei. "From Crystal to Columnar Discotic Liquid Crystal Phases: Phase Structural Characterization of Series of Novel Phenazines Potentially Useful in Organic Electronics." Akron, OH : University of Akron, 2009. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=akron1247614330.
Повний текст джерелаАнотація:
Dissertation (Ph. D.)--University of Akron, Dept. of Polymer Science, 2009."August, 2009." Title from electronic dissertation title page (viewed 9/23/2009) Advisor, Stephen Z. D. Cheng; Committee members, Alexei P. Sokolov, Gustavo A. Carri, Darrell H. Reneker, Weiping Zheng; Department Chair, Ali Dhinojwala; Dean of the College, Stephen Z. D. Cheng; Dean of the Graduate School, George R. Newkome. Includes bibliographical references.
10
Sapelkin, Andrei V. "Structure of and phase transformations in bulk amorphous (GaSb)â†1â†-â†x(Geâ†2)â†x." Thesis, De Montfort University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.391341.
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11
BALDACIM, SANDRO A. "Desenvolvimento, processamento e caracterizacao de compositos ceramicos Sisub(3)Nsub(4)-SiCsub(w)." reponame:Repositório Institucional do IPEN, 2000. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10877.
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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
12
CAIRO, CARLOS A. A. "Desenvolvimento de um sistema de protecao antioxidante para o composito carbono-carbono." reponame:Repositório Institucional do IPEN, 1998. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10687.
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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
13
Artigas, Alava Miguel José. "Contribution à l'étude du polymorphisme des phases MM'X (M,M' = métaux de transition, X=P, As)." Grenoble 1, 1992. http://www.theses.fr/1992GRE10133.
Повний текст джерелаАнотація:
L'existence de nouvelles varietes polymorphiques a structures cristallines plus complexes que celles des types fondamentaux fe#2as,fe#2p et co#2p nous a conduit a proposer une vue cristallochimique generalisee des phases mm'x. Leurs structures sont decrites en terme de polytypes qui peuvent etre engendres par differentes combinaisons d'une unite structurale pseudo-rhomboedrique, ce qui a permis d'envisager des modeles idealises pour les nouveaux polytypes. L'etude cristallographique des nouveaux polytypes de fepdp,ferhp et co#2as permet alors, par comparaison avec le modele idealise, d'analyser les ecarts a l'idealite. On met ainsi en relief la formation d'amas d'atomes caracterises par une surconcentration locale de palladium ou de rhodium autour d'un atome de phosphore (ou une contraction des atomes de cobalt autour d'un atome d'arsenic dans co#2as). Ces amas observes egalement dans d'autres polytypes superieurs permettent de penser que leurs formations et leurs structures associees sont le resultat de la forte cohesion apportee par le remplissage des etats d avec l'appoint d'un renforcement de l'hybridation d-p. Un deuxieme type de polymorphisme est le resultat de la deformation de la structure de fe#2p. Il apparait sous deux formes: l'une de type tifesi, l'autre de type cr#2p. Nous avons precise cette derniere par une etude cristallographique et effectue leur comparaison sur la base de nos modeles structuraux. Dans l'evolution structurale systematique en fonction du renforcement des interactions metalliques, fe#2p apparait de nouveau comme une structure intermediaire entre les types fe#2as et co#2p. La deformation de cr#2p constitue un premier pas en direction de fe#2as, la deformation de tifesi, en direction de co#2p
14
Грищенко, Вікторія Андріївна. "Вплив йонного опромінення на структурно-фазові перетворення в тонких плівках Cu/Cr, Ni/Cr, Ni/Cu/Cr при термічному відпалі". Master's thesis, КПІ ім. Ігоря Сікорського, 2020. https://ela.kpi.ua/handle/123456789/34696.
Повний текст джерелаАнотація:
Магістерська дисертація: 81 сторінка, 41 рисунків, 12 таблиць, 38 літературних джерел.
Об’єкт досліджень:структурно-фазові перетворення в наношарових композиціях Cu/Cr, Ni/Cr, Ni/Cu/Cr за умов вакуумного термічного відпалу та з додатковою йонно-плазмовою обробкою.
Мета роботи: дослідження особливостей впливу попередньої йонно-плазмової обробки на структурно-фазові перетворення у тонких плівках Cu/Cr, Ni/Cr, Ni/Cu/Crза умов термічного відпалу.
Методи дослідження: мас-спектрометрія вторинних йонів, трансмісійна електронна мікроскопія, in-situ високоенергетична електронна дифракція.
Досліджено особливості формування структури та фазового складу систем Cu/Cr, Ni/Cr та Ni/Cu/Cr при відпалі у вакуумі у широкому температурному інтервалі.
Тонкоплівкові композиції були одержані шляхом термічного випаровування у вакуумі і, в подальшому, піддавалися йонно-плазмовій та термічній обробці до температур 690 °C. Після обробки плівки досліджено методами мас-спектрометрії вторинних йонів, трансмісійною електронною мікроскопією, in-situ високоенергетичною електронною дифракцією.
Зафіксовано розвиток окисно-відновних процесів, які ефективно контролюються шляхом використання додаткового плазмового оброблення плівок. Йонний низькоенергетичний вплив стабілізує структуру досліджуваних систем шляхом гальмування процесів рекристалізації.Master thesis: 81 pages, 41 figure, 12 tables, 38 references. The object of research is structural-phase transformations in nanolayer compositions Cu/Cr, Ni/Cr, Ni/Cu/Cr under conditions of vacuum thermal annealing and with additional ion-plasma action. The purpose is to study the peculiarities of the influence of preliminary ion plasma action on structural-phase transformations in thin films Cu/Cr, Ni/Cr, Ni/Cu/Cr under conditions of thermal annealing. Research methods: secondary-ion mass spectrometry, transmission electron microscopy, in-situ high-energy electron diffraction. The peculiarities of the formation of the structure and phase composition of the Cu/Cr, Ni/Cr and Ni/Cu/Cr systems during annealing in vacuum in a wide temperature range have been studied. The thin film compositions were obtained by thermal evaporation in vacuum and subsequently subjected to ion-plasma and heat treatment to temperatures of 690 °C. After processing the film, it was investigated by secondary-ion mass spectrometry, transmission electron microscopy, in-situ high-energy electron diffraction. The development of redox processes, which are effectively controlled by the use of additional plasma treatment of films, has been recorded. Ionic low-energy effect stabilizes the structure of the studied systems by inhibiting recrystallization processes.
15
Cheerkapally, Raghavender P. "Surface-induced structural transformations in titanium nanowires." University of Cincinnati / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1384869599.
Повний текст джерела
16
Schmidt, Marek Wojciech, and Marek Schmidt@rl ac uk. "Phase formation and structural transformation of strontium ferrite SrFeOx." The Australian National University. Research School of Physical Sciences and Engineering, 2001. http://thesis.anu.edu.au./public/adt-ANU20020708.190055.
Повний текст джерелаАнотація:
Non-stoichiometric strontium iron oxide is described by an abbreviated formula SrFeOx (2.5 ≤ x ≤ 3.0) exhibits a variety of interesting physical and chemical properties over a broad range of temperatures and in different
gaseous environments. The oxide contains a mixture of iron in the trivalent and the rare tetravalent state. The material at elevated temperature is a mixed oxygen conductor and it, or its derivatives,can have practical
applications in oxygen conducting devices such as pressure driven oxygen
generators, partial oxidation reactors in electrodes for solid oxide fuel cells
(SOFC).
¶
This thesis examines the behaviour of the material at ambient and elevated temperatures using a broad spectrum of solid state experimental
techniques such as: x-ray and neutron powder diffraction,thermogravimetric and calorimetric methods,scanning electron microscopy and Mossbauer
spectroscopy. Changes in the oxide were induced using conventional thermal
treatment in various atmospheres as well as mechanical energy (ball milling).
The first experimental chapter examines the formation of the ferrite from
a mixture of reactants.It describes the chemical reactions and phase transitions that lead to the formation of the oxide. Ball milling of the reactants prior to annealing was found to eliminate transient phases from the reaction route and to increase the kinetics of
the reaction at lower temperatures.
Examination of the thermodynamics of iron oxide (hematite) used for the
reactions led to a new route of synthesis of the ferrite frommagnetite and
strontium carbonate.This chapter also explores the possibility of synthesis
of the material at room temperature using ball milling.
¶
The ferrite strongly interacts with the gas phase so its behaviour was studied under different pressures of oxygen and in carbon dioxide.The changes in ferrite composition have an equilibrium character and depend on temperature and oxygen concentration in the
atmosphere. Variations of the oxygen
content x were described as a function of temperature and oxygen partial
pressure, the results were used to plot an equilibrium composition diagram.
The heat of oxidation was also measured as a function of temperature and oxygen partial pressure.
¶
Interaction of the ferrite with carbon dioxide below a critical temperature
causes decomposition of the material to strontium carbonate and SrFe12O19 .
The critical temperature depends on the partial pressure of CO2 and above
the critical temperature the carbonate and SrFe12O19 are converted back into
the ferrite.The resulting SrFe12O19 is very resistant towards carbonation and
the thermal carbonation reaction does not lead to a complete decomposition
of SrFeOx to hematite and strontium carbonate.
¶
The thermally induced oxidation and carbonation reactions cease at room
temperature due to sluggish kinetics however,they can be carried out at ambient temperature using ball milling.The reaction routes for these processes are different from the thermal routes.The mechanical oxidation induces two
or more concurrent reactions which lead to samples containing two or more
phases. The mechanical carbonation on the other hand produces an unknown
metastable iron carbonate and leads a complete decomposition of the ferrite
to strontiumcarbonate and hematite.
¶
Thermally and mechanically oxidized samples were studied using Mossbauer
spectroscopy. The author proposes a new interpretation of the Sr4Fe4O11
(x=2.75) and Sr8Fe8O23 (x=2.875)spectra.The interpretation is based
on the chemistry of the compounds and provides a simpler explanation of
the observed absorption lines.The Mossbauer results froma range of compositions
revealed the roomtemperature phase behaviour of the ferrite also
examined using x-ray diffraction.
¶
The high-temperature crystal structure of the ferrite was examined using
neutron powder diffraction.The measurements were done at temperatures
up to 1273K in argon and air atmospheres.The former atmosphere protects
Sr2Fe2O5 (x=2.5) against oxidation and the measurements in air allowed
variation of the composition of the oxide in the range 2.56 ≤ x ≤ 2.81.
Sr2Fe2O5 is an antiferromagnet and undergoes phase transitions to the paramagnetic
state at 692K and from the orthorhombic to the cubic structure
around 1140K.The oxidized formof the ferrite also undergoes a transition
to the high-temperature cubic form.The author proposes a new structural
model for the cubic phase based on a unit cell with the Fm3c symmetry.
The new model allows a description of the high-temperature cubic form of
the ferrite as a solid solution of the composition end members.The results
were used to draw a phase diagramfor the SrFeOx system.
¶
The last chapter summarizes the findings and suggests directions for further research.
17
Byakova, A. V., V. V. Cherednichenko, A. A. Scheretskiy, A. A. Vlasov, and A. I. Yurkova. "Structural Evolution and Phase Transformation in Nanoquasicrystalline Al-Fe-Cr Alloy: DSC Analysis." Thesis, Sumy State University, 2012. http://essuir.sumdu.edu.ua/handle/123456789/34854.
Повний текст джерелаАнотація:
Kinetic parameters for microstructural evolution and phase transformation in water atomized Al-Fe-Cr
based alloy with nominal composition Al94Fe3Cr3 have been examined by means of developed precise method
of DSC technique and confirmed by the results of XRD analysis. Two exothermic reactions including that
with a maximum at 380 – 400 degrees Celsius has been ascribed to dislocation reorganisation and recrystallisation process within the Al matrix although the main exothermic reaction with a maximum around 540 degrees Celsius arose
from decomposition of icosahedral quasicrystalline particles and simultaneous formation of the metastable
Al6Fe phase and more stable crystalline particles compositionally corresponded to the O-Al13Cr2 and
O-Al13Fe4 phases. Activation energy for the main exothermic reaction has been found to be roughly
about 53.1 kJ mol-1 which is significantly smaller than that for the bulk diffusion of either iron or chromium atoms in aluminium and very close to that for the vacancy migration.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/34854
18
Chan, Fung Choy. "Powder X-ray diffraction studies of structural and kinetic aspects of polymorphism." Thesis, King's College London (University of London), 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.327050.
Повний текст джерела
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Haskel, Daniel. "Local structural studies of oriented high temperature superconducting cuprates by polarized XAFS spectroscopy /." Thesis, Connect to this title online; UW restricted, 1998. http://hdl.handle.net/1773/9712.
Повний текст джерела
20
Dunn, James A. "From organometallic cations to carbenes : an NMR, structural and reactivity study /." *McMaster only, 1998.
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21
Flores, Roxana Lili Roque. "Caracterização do estado sólido de ganciclovir." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/9/9139/tde-16112017-173605/.
Повний текст джерелаАнотація:
O presente trabalho teve como objetivo o estudo do estado sólido do ganciclovir (GCV) e suas diferentes formas polimórficas. O GCV é um fármaco antiviral útil no tratamento de infecções por citomegalovírus (CMV). Embora seja um fármaco amplamente usado, poucos estudos têm sido realizados sobre seu estado sólido. Atualmente, o GCV é conhecido por apresentar quatro formas cristalinas, duas anidras (Forma I e II) e duas hidratas (III e IV). Neste trabalho, nós reportamos a solução da estrutura cristalográfica da Forma I do GCV, que foi encontrado durante o screening de cristalização do fármaco, em que nove ensaios de cristalização (GCV-1, GCV-A, GCV-B, GCV-C, GCV-D, GCV-E, GCV-F, GCV-G e GCV-H) foram realizados e os materiais resultantes foram caracterizados por Difratometria de raios X (DRX), análise térmica (DTA/TG) e Hot Stage Microscopy. De todas as cristalizações realizadas foram obtidas quatro formas sólidas, denominadas como Forma I (GCV-1, GCV-B e GCV-H), Forma III (GCV-C, GCV-D, GCV-F e GCV-G), Forma IV (GCV-A) e Forma V (GCV-E). Esta última está sendo descrita pela primeira vez na literatura e indica a presença de outra forma hidratada de GCV. As Formas I, III e IV corresponderam a forma anidra e as duas formas hidratadas do fármaco, respectivamente. Além disso, foi evidenciado por experimentos de conversão de slurry e análise térmica que o cristalizado de GCV-1 (Forma I) foi o mais estável entre os materiais obtidos, e este deu origem ao monocristal da Forma I de GCV, estrutura cristalina anidra do fármaco. Neste trabalho, pela primeira vez, a estrutura cristalina deste composto foi definida por cristalografia de raios X de monocristal. A análise estrutural mostrou que a Forma I do fármaco cristaliza no grupo espacial monoclínico P21/c e está composta por quatro moléculas de GCV na sua unidade assimétrica. Cada molécula está unida intermolecularmente por ligações de hidrogênio, que dão lugar à formação de cadeias infinitas e estas por sua vez se arranjam de maneira a formar uma estrutura tridimensional.This presented work aims to study the solid state of ganciclovir (GCV) and its different polymorphic forms. GCV is an antiviral drug useful in the treatment of cytomegalovirus (CMV) infections. Although it is a widely-used drug, few studies have been conducted on its solid state. Currently, GCV is known to have four crystalline forms, two anhydrous (Form I and II) and two hydrates (III and IV). In this investigation, we report a successful preparation of GCV Form I and its crystallographic structure, which was found during the crystallization of the drug, in which nine crystallization tests (GCV-1, GCV-A, GCV-B, GCV- D, GCV-E, GCV-F, GCV-G and GCV-H) were performed and the resulting materials were characterized by X-ray diffractometry (XRD), thermal analysis (DTA/TG) and Hot Stage Microscopy. Of all the crystallizations performed, four solid forms were obtained, denoted as Form I (GCV-1, GCV-B and GCV- H), Form III (GCV-C, GCV-D, GCV-F and GCV-G), Form IV (GCV-A) and Form V (GCV-E). The latter is being described for the first time in the literature and indicates the presence of another hydrated form of GCV. Forms I, III and IV corresponded to the anhydrous form and the two hydrated forms of the drug, respectively. In addition, it was evident by both the slurry conversion and the thermal analysis methods that the GCV-1 crystallized (Form I) was indeed the most stable amongst the materials obtained. This gave rise to GCV Form I monocrystal, anhydrous crystalline structure of the drug. The compound was characterized by monocrystal X-ray crystallography. The structural analysis showed that Form I of the drug crystallized in the monoclinic system space group P21/c is composed of four molecules of GCV in its asymmetric unit. Each molecule is linked intermolecularly by hydrogen bonds, which give rise to the formation of infinite chains arranged in a way that form a three-dimensional structure.
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Lodini, Alain. "Contribution a l'etude de l'instabilite de phase de deux alliages cuivreux a durcissement structural et a memoire de forme au cours d'une deformation plastique : application au soudage par faisceau d'electrons." Reims, 1987. http://www.theses.fr/1987REIMS015.
Повний текст джерелаАнотація:
Analyse des mecanismes de transformation par des methodes physiques complementaires: dilatometrie, calorimetrie, microscopie electronique, diffraction rx, electronique et neutronique. Analyse de la precipitation dans l'alliage cu-1% cr-zr. Influence de la deformation sur le mecanisme de precipitation. Interpretation thermodynamique du phenomene. Etude du mecanisme de deformation dans l'alliage cu-12,6% al a l'etat martensitique. Determination des transformations de phase et developpement d'un effet de memoire de forme. Ces transformations structurales sont a l'origine de la fragilisation des cordons de soudure au cours d'une operation de soudage par faisceau d'electrons
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Casalena, Lee. "Multimodal Nanoscale Characterization of Transformation and Deformation Mechanisms in Several Nickel Titanium Based Shape Memory Alloys." The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1499568013015563.
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Jouanneaux, Alain. "Etude par r. P. E. De diffraction de neutrons des composes mixtes rb : :(x)(nh::(4))::(1-x)alf::(4), desordre chimique, transition de phase, ordre local, verre de spin structural." Nantes, 1987. http://www.theses.fr/1987NANT2044.
Повний текст джерелаАнотація:
Mise en evidence, a temperature ambiante, de la substitution de rb**(+) a toute concentration. Determination par diffraction de neutrons sur poudre de la structure moyenne des cristaux mixtes : resultats en accord avec les resultats rpe. Puis, etude a basse temperature de l'ordre du sous-reseau des ions nh::(4)**(+) pour 0
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Kuo, Meng-Hsin, and 郭孟鑫. "Synthesis and Structural Transformations of Mg-Zn-Al Quasicrystalline Phase." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/23810480712079309975.
Повний текст джерелаАнотація:
碩士大同大學
材料工程學系(所)
94
In this research it is intended to synthesize the powders of various intermediate phases and icosahedral quasicrystal in Mg-Zn-Al system by mechanical alloying (MA) technique. With X-ray diffraction and thermal analysis as the analytical tools, the composition ranges and formation conditions of the various intermediate and quasicrystalline phases in the Mg-Al-Zn system synthesized by MA were investigated in this study. The milling and annealing behavior of Mg-Zn-Al ternary powders in the composition ranges in the neighborhood of the �� phase and �� phase were investigated. For composition of Mg55Zn22.5Al22.5, the icosahedral quasicrystalline phase starts to appear when the milling was lasted for 2.5 hr. It seems that the relative contents of Mg, Zn and Al in the starting powders might affect the alloying behavior in a quite different way. Non-equilibrium solid-state milling like mechanical alloying can create the i-phase from the non-stoichiometric composition. With increase in Zn content in the initial powder composition, the equilibrium structure obtained after annealing the milled powders is the MgZn2 phase. On the other hand, with increase in Al content, Mg32(Al,Zn)49 is the structure obtained after annealing. The annealing of the milled powders at lower temperature creates MgZn2 phase. However, this phase is converted to Mg32(Al,Zn)49 phase upon annealing at higher temperature. Namely the Mg32(Al,Zn)49 phase is obtained through transforming the MgZn2 phase at higher temperature.
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Munawar, Iram. "Structural and magnetic phase transitions in hexagonal perovskites /." 2004.
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Chung, Han, and 鍾翰. "The Stress-Induced Structural Phase Transformations of Micro-Crystalline Silicon Films During Nanoindentation." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/46424263296384139999.
Повний текст джерелаАнотація:
碩士遠東科技大學
機械工程研究所在職專班
100
In the present study, the theoretical model for contact stress and contact strain arising at nanoindentations with various indentation depths is developed. The nanoindentations were applied to island-shaped regions with metal-induced Si crystallizations, which were generated in Al/a-Si(amorphous Si)/Glass 7740 specimens that were annealed at 500 °C with Al film etched off. The experimental stress-strain relationship is obtained from the load-depth profile in order to investigate the critical stresses arising at various phase transitions. The values at various indentation depths are applied to determine the Gibbs free energy at various phases. The intersections of the Gibbs free energy lines are used to determine the possible paths of phase transitions arising at various indentation depths. The final phases predicted by the proposed model are confirmed by TEM diffraction patterns and Raman spectra. The proposed model is thus valid for predicting contact parameters using nanoindentations.
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Thawabi, Hassan S. "Ab-initio First Principle Modeling of Structural and Magnetic Phase Transformations in Co-Ni-Al Based Shape Memory Alloys." Thesis, 2013. http://hdl.handle.net/1969.1/149454.
Повний текст джерелаАнотація:
Ferromagnetic shape memory alloys FSMAs have diverse application, especially in the aerospace and bio-medical industries. They are a class of active and smart materials exhibiting strains under the influence of an applied magnetic field. These magnetic properties are mainly attributed to the martensitic structural phase trans- formation these material experience in response to temperature variation. Co-Ni-Al based alloys are one of the most promising ferromagnetic shape memory alloy FSMA that has been put recently under extensive study by researchers. They have shown extensive and promising features specifically those related to self-actuation.
The effect of valence electron concentration and magnetic properties of Co-Ni-Al based ferromagnetic shape memory alloys on the martensitic transformations were analyzed utilizing Ab-initio first principle calculations. The variations of martensite start temperatures (Ms) and magnetic properties of a number of stoichiometric and mnon-stoichiometric Co-Ni-Al ferromagnetic shape memory alloys (FSMA’s) with B2 austenite structure were studied and analyzed as a function of composition and lattice site ordering and site preference. A major conclusion of this thesis suggests that the magnetic valence number (Zm) should be considered in conjunction to the e/a ratio if the composition profile of the Ms is to be determined. Both Monte-Carlo and Ab-initio simulations were implemented to obtain the magnetic Heisenberg’s exchange coupling parameters (J m) and model the magnetic transformations in stoichiometric Co2NiAl FSMAs. Two different cubic structures, ordered and disordered were compared to their tetragonal distortions martensitic phases and their Curie temperature (TC ) were obtained from the Monte-Carlo magnetic susceptibility temperature profile.
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Sun, Xinxing. "Phase Transformations and Switching of Chalcogenide Phase-change Material Films Prepared by Pulsed Laser Deposition." Doctoral thesis, 2016. https://ul.qucosa.de/id/qucosa%3A15633.
Повний текст джерелаАнотація:
The thesis deals with the preparation, characterization and, in particular, with the switching properties of phase-change material (PCM) thin films. The films were deposited using the Pulsed Laser Deposition (PLD) technique. Phase transformations in these films were triggered by means of thermal annealing, laser pulses, and electrical pulses. The five major physical aspects structure transformation, crystallization kinetics, topography, optical properties, and electrical properties have been investigated using XRD, TEM, SEM, AFM, DSC, UV-Vis spectroscopy, a custom-made nanosecond UV laser pump-probe system, in situ resistance measurements, and conductive-AFM.
The systematic investigation of the ex situ thermally induced crystallization process of pure stoichiometric GeTe films and O-incorporating GeTe films provides detailed information on structure transformation, topography, crystallization kinetics, optical reflectivity and electrical resistivity. The results reveal a significant improvement of the thermal stability in PCM application for data storage. With the aim of reducing the switching energy consumption and to enhance the optical reflectivity contrast by improving the quality of the produced films, the growth of the GeTe films with simultaneous in situ thermal treatment was investigated with respect to optimizing the film growth conditions, e.g. growth temperature, substrate type.
For the investigation of the fast phase transformation process, GeTe films were irradiated by ns UV laser pulses, tailoring various parameters such as pulse number, laser fluence, pulse repetition rate, and film thickness. Additionally, the investigation focused on the comparison of crystallization of GST thin films induced by either nano- or femtosecond single laser pulse irradiation, used to attain a high data transfer rate and to improve the understanding of the mechanisms of fast phase transformation.
Non-volatile optical multilevel switching in GeTe phase-change films was identified to be feasible and accurately controllable at a timescale of nanoseconds, which is promising for high speed and high storage density of optical memory devices. Moreover, correlating the dynamics of the optical switching process and the structural information demonstrated not only exactly how fast phase change processes take place, but also, importantly, allowed the determination of the rapid kinetics of phase transformation on the microscopic scale.
In the next step, a new general concept for the combination of PCRAM and ReRAM was developed. Bipolar electrical switching of PCM memory cells at the nanoscale can be achieved and improvements of the performance in terms of RESET/SET operation voltage, On/Off resistance ratio and cycling endurance are demonstrated. The original underlying mechanism was verified by the Poole-Frenkel conduction model. The polarity-dependent resistance switching processes can be visualized simultaneously by topography and current images. The local microstructure on the nanoscale of such memory cells and the corresponding local chemical composition were correlated.
The gained results contribute to meeting the key challenges of the current understanding and of the development of PCMs for data storage applications, covering thin film preparation, thermal stability, signal-to-noise ratio, switching energy, data transfer rate, storage density, and scalability.
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Chen, Wei-Ting, and 陳韋廷. "Study on Structural Evolution and Phase Transformation of Au-Ag Alloy Nanoparticle Deposits." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/97376371679450407237.
Повний текст джерелаАнотація:
碩士國立東華大學
材料科學與工程學系
99
Using the Brust-Schiffrin two-phase method, this study synthesized thiol-protected nanoparticles of Au, Ag and their alloys (Au3Ag、AuAg及Ag3Au) and systematically investigated the structural evolution and phase transformation of nanoparticle deposits (NPD) upon heating by means of in situ synchrotron radiation X-ray diffraction. The relationships between the coalescence of nanoparticles, the optical and electrical properties of cured deposits, as well as the surfactant reactions, were also clarified. Experimental results show that there existed a critical temperature ranging from 120oC to 164oC, above which the broad and weak X-ray diffraction peaks became sharp and strong. The coalescence of nanoparticles through surface melting accounted for this. It was also demonstrated that the critical coalescent temperature for the Au-Ag alloy nanoparticle deposits was apparently lower than that for pure metals. With a greater Ag content, the grain size and electrical resistance of the cured NPDs were raised. From the viewpoints of thermodynamics and chemistry, the aforementioned phenomena were discussed and explained.
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Lee, Bong-Sub. "Optical and electronic properties, nanoscale structural order, and transformation kinetics of phase change materials /." 2006. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3242913.
Повний текст джерелаАнотація:
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2006.Source: Dissertation Abstracts International, Volume: 67-11, Section: B, page: 6674. Adviser: John R. Abelson. Includes bibliographical references. Available on microfilm from Pro Quest Information and Learning.
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Chin, Huang Kwo, and 黃國欽. "A Study on Modeling of SMA Dynamics Including Thermal, Phase Transformation, and Structural Effects." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/48598561196537150993.
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Irshad, H. M., B. A. Ahmed, M. A. Ehsan, Tahir I. Khan, T. Laoui, M. R. Yousaf, A. Ibrahim, and A. S. Hakeem. "Investigation of the structural and mechanical properties of micro-/nano-sized Al2O3 and cBN composites prepared by spark plasma sintering." 2017. http://hdl.handle.net/10454/17078.
Повний текст джерелаАнотація:
YesAlumina-cubic boron nitride (cBN) composites were prepared using the spark plasma sintering (SPS) technique. Alpha-alumina powders with particle sizes of ∼15 µm and ∼150 nm were used as the matrix while cBN particles with and without nickel coating were used as reinforcement agents. The amount of both coated and uncoated cBN reinforcements for each type of matrix was varied between 10 to 30 wt%. The powder materials were sintered at a temperature of 1400 °C under a constant uniaxial pressure of 50 MPa. We studied the effect of the size of the starting alumina powder particles, as well as the effect of the nickel coating, on the phase transformation from cBN to hBN (hexagonal boron nitride) and on the thermo-mechanical properties of the composites. In contrast to micro-sized alumina, utilization of nano-sized alumina as the starting powder was observed to have played a pivotal role in preventing the cBN-to-hBN transformation. The composites prepared using nano-sized alumina reinforced with nickel-coated 30 wt% cBN showed the highest relative density of 99% along with the highest Vickers hardness (Hv2) value of 29 GPa. Because the compositions made with micro-sized alumina underwent the phase transformation from cBN to hBN, their relative densification as well as hardness values were relatively low (20.9–22.8 GPa). However, the nickel coating on the cBN reinforcement particles hindered the cBN-to-hBN transformation in the micro-sized alumina matrix, resulting in improved hardness values of up to 24.64 GPa.