Добірка наукової літератури з теми "Borate Based Glasses"

In glass materials, Poisson’s ratio (ν) has been proposed to be correlated with a variety of features, including atomic packing density (Cg), liquid fragility (m), and network connectivity. To further investigate these correlations in oxide glasses, here, we study cesium borate and cesium silicate glasses with varying modifier/former ratio given the difference in network former coordination and because cesium results in relatively high ν compared to the smaller alkali modifiers. Within the binary glass series, we find positive correlations between ν on one hand and m and Cg on the other hand. The network former is found to greatly influence the correlation between ν and the number of bridging oxygens (nBO), with a negative correlation for silicate glasses and positive correlation for borate glasses. An analysis based on topological constraint theory shows that this difference cannot be explained by the effect of superstructural units on the network connectivity in lithium borate glasses. Considering a wider range of oxide glasses from the literature, we find that ν generally decreases with increasing network connectivity, but with notable exceptions for heavy alkali borate glasses and calcium alumino tectosilicate glasses.

Theoretical calculations of mass attenuation coefficients, partial interactions, atomic cross-section, and effective atomic numbers of PbO-based silicate, borate, and phosphate glass systems have been investigated at 662 keV. PbO-based silicate glass has been found with the highest total mass attenuation coefficient and then phosphate and borate glasses, respectively. Compton scattering has been the dominate interaction contributed to the different total attenuation coefficients in each of the glass matrices. The silicate and phosphate glass systems are more appropriate choices as lead-based radiation shielding glass than the borate glass system. Moreover, comparison of results has shown that the glasses possess better shielding properties than standard shielding concretes, suggesting a smaller size requirement in addition to transparency in the visible region.

When oxide glasses are modified by dissimilar alkali ions, a maximum in the electric resistivity or the expansion coefficient appears, called the mixed-alkali effect (MAE). This paper reviews the MAE on the thermal, elastic, and vibrational properties of the mixed-cesium lithium borate glasses, x{(1−y)Cs2O-yLi2O}-(1−x)B2O3. For the single-alkali borate glasses, xM2O(1−x)-B2O3 (M = Li, Na, K, Rb, and Cs), the glass transition temperature, Tg = 270 °C, of a borate glass monotonically increases as the alkali content x increases. However, for the mixed-cesium lithium borate glasses the Tg shows the minimum against the lithium fraction y. The dependences of the elastic properties on the lithium fraction y were discussed regarding the longitudinal modulus, Poisson’s ratio, and Cauchy-type relation. The internal vibrational bands related to the boron-oxide structural groups and the splitting of a boson peak were discussed based on Raman scattering spectroscopy. The MAE on various physical properties are discussed on the basis of the changes in the coordination number of the borons and the nonbridging oxygens caused by the dissimilar alkali ions.

Phosphate glasses generally have lower glass-transition temperatures and greater thermal-expansion coefficients than silicate and borate glasses, and so are candidate materials for specialty glass-metal sealing applications. Phosphate glasses also have desirable optical properties (rare-earth stimulated-emission cross sections, low thermo-optical coefficients, ultraviolet transparency, etc.) and so are used as laser glasses. Recent developments of novel compositions for biomedical applications and as fast-ion conductors have also revived interest in the study of phosphate glass structures.The structure/property relationships in simple phosphate glasses have not received nearly the attention paid to silicate and borate-based systems. This is partially due to the difficulty in preparing anhydrous compositions with more than 50-mol% P2O5. Ultraphosphate compositions (where the [O]/[P] ratio is less than 3) are highly reactive to ambient water. In addition because P2O5 sublimes at about 300°C, ultraphosphate glasses have not been studied to the extent that metaphosphate ([O]/[P] = 3) and polyphosphate ([O]/[P] > 3) compositions have.

The results presented in this communication concern visible and near-IR emission of Pr3+ ions in selected inorganic glasses, i.e., borate-based glass with Ga2O3 and BaO, lead-phosphate glass with Ga2O3, gallo-germanate glass modified by BaO/BaF2, and multicomponent fluoride glass based on InF3. Glasses present several emission bands at blue, reddish orange, and near-infrared spectral ranges, which correspond to 4f–4f electronic transitions of Pr3+. The profiles of emission bands and their relative intensity ratios depend strongly on glass-host. Visible emission of Pr3+ ions is tuned from red/orange for borate-based glass to nearly white light for multicomponent fluoride glass based on InF3. The positions and spectral linewidths for near-infrared luminescence bands at the optical telecommunication window corresponding to the 1G4 → 3H5, 1D2 → 1G4, and 3H4 → 3F3,3F4 transitions of Pr3+ are dependent on glass-host matrices and excitation wavelengths. Low-phonon fluoride glasses based on InF3 and gallo-germanate glasses with BaO/BaF2 are excellent candidates for broadband near-infrared optical amplifiers. Spectroscopic properties of Pr3+-doped glasses are compared and discussed in relation to potential optical applications.

Lithium borate glasses modified with molybdenum oxide according to the formula: xMoO3 (1-x)[0.25 Li2O 0.75 B2O3] prepared by the melt quenching technique were studied. Density, differential thermal analysis, FTIR and impedance spectroscopic were used to analyze these systems. It was confirmed that the glassy matrix of these systems was based on the MoO6 octahedral units and on BO3 and BO4 units. The results explained how the stability of a borate matrix that hosted molybdenum ions was affected by the presence of small mobile ions (lithium ions in the present case). It was found that concentration of molybdenum oxide was restricted by strong interactions between the charged molybdenum structures and the mobile ions due to the presence of order forces that promote the formation of crystalline structures. Keywords: molybdenum, oxide glasses, electrical properties, borate glass stability

Two completely different glass-host matrices containing lead, i.e. borate and germanate glasses doped with erbium were studied. Replacement of glass-former B2O3 by GeO2 in amorphous host was evidenced by optical methods. The luminescence decay from the 4I13/2 upper laser state of Er3+ ions is relatively short, whereas up-converted emission signal is reduced definitely in borate glass containing lead due to its high B-O stretching vibrations. The results indicate that germanate glasses containing lead are promising for near-infrared luminescence and up-conversion applications. Full Text: PDF ReferencesR. Balda, A. Oleaga, J. Fernandez, J.M. Fdez-Navarro, "Spectroscopy and frequency upconversion of Er3+ ions in lead niobium germanate glasses", Opt. Mater. 24, 83 (2003). CrossRef H. Yamauchi, Y. Ohishi, "Spectroscopic properties of Er3+-doped PbO?Ga2O3?GeO2 glass for optical amplifiers", Opt. Mater. 27, 679 (2005). CrossRef W.A. Pisarski, Ł. Grobelny, J. Pisarska, R. Lisiecki, W. Ryba-Romanowski, "Spectroscopic properties of Yb3+ and Er3+ ions in heavy metal glasses", J. Alloys Compd. 509, 8088 (2011). CrossRef M.B. Saisudha, J. Ramakrishna, "Effect of host glass on the optical absorption properties of Nd3+, Sm3+, and Dy3+ in lead borate glasses", Phys. Rev. B 53, 6186 (1996). CrossRef C.K. Jayasankar, V. Venkatramu, S. Surendra Babu, P. Babu, "Luminescence properties of Dy3+ ions in a variety of borate and fluoroborate glasses containing lithium, zinc, and lead", J. Alloys Compd. 374, 22 (2004). CrossRef W.A. Pisarski et al. "Luminescence spectroscopy of rare earth-doped oxychloride lead borate glasses", J. Lumin. 131, 649 (2011). CrossRef M. Kochanowicz, W. Mazerski, J. Żmojda, K. Czajkowski, D. Dorosz, "Green upconversion emission in tellurite optical fibre codoped with Yb3+/Er3+", Phot. Lett. Poland 5, 35 (2013). CrossRef J. Dorosz, "Novel constructions of optical fibers doped with rare ? earth ions", Ceramics 86 (2005). CrossRef J. Żmojda, D. Dorosz, M. Kochanowicz, J. Dorosz, "Spectroscopic properties of Yb3+/Er3+ - doped antimony-phosphate glasses for fiber amplifiers", Phot. Lett. Poland 2, 76 (2010). CrossRef J. Dorosz, R. S. Romaniuk, "Development of Optical Fiber Technology in Poland", INTL J. Electron. Telecom. 57, 191 (2011). CrossRef Q.Y. Zhang et al. "Effects of PbF2 doping on structure and spectroscopic properties of Ga2O3?GeO2?Bi2O3?PbO glasses doped with rare earths", J. Appl. Phys. 99, 033510 (2006) CrossRef W.A. Pisarski, G. Dominiak-Dzik, W. Ryba-Romanowski, J. Pisarska, "Role of PbO substitution by PbF2 on structural behavior and luminescence of rare earth-doped lead borate glass", J. Alloys Compd. 451, 220 (2008). CrossRef M. Sołtys, J. Pisarska, L. Żur, T. Goryczka, W.A. Pisarski, "Influence of M2O3 (M = Al, Ga) glass modifiers on structure, thermal and spectroscopic properties of rare earth ions in lead phosphate based systems", Proc. SPIE 9228, 92280A (2014). CrossRef J. Janek, J. Pisarska, W.A. Pisarski, "Rare earth doped lead-free germanate glasses for modern photonics", Phot. Lett. Poland 6, 71 (2014). CrossRef W.A. Pisarski et al. "Infrared-to-visible conversion luminescence of Er3+ ions in lead borate transparent glass-ceramics", Opt. Mater. 31, 1781 (2009). CrossRef J. Pisarska, L. Żur, W.A. Pisarski, "Optical spectroscopy of Dy3+ ions in heavy metal lead-based glasses and glass?ceramics", J. Mol. Struct. 993, 160 (2011). CrossRef L. Żur, M. Sołtys, J. Pisarska, W.A. Pisarski, "Absorption and luminescence properties of terbium ions in heavy metal glasses", J. Alloys Compd. 578, 512 (2013). CrossRef W.A. Pisarski, L. Żur, M. Kowal, J. Pisarska, "Enhancement and quenching photoluminescence effects for rare earth ? Doped lead bismuth gallate glasses", J. Alloys Compd. 651, 565 (2015). CrossRef M. Shojiya, Y. Kawamoto, K. Kadono, "Judd?Ofelt parameters and multiphonon relaxation of Ho3+ ions in ZnCl2-based glass", J. Appl. Phys. 89, 4944 (2001). CrossRef

Faraday rotation (FR) and magnetic circular dichroism (MCD) of nanocomposite structures based on potassium-aluminum-germanium-boron glasses co-doped with Fe and rare earth (RE) or Y+Bi oxides have been studied. Formation of magnetic nanoparticles as a result of the glass heat treatment ensures them magnetic and magneto-optical properties typical of magnetically ordered substances. At the same time, glasses keep transparence in visual spectral range owing to low paramagnetic oxides concentration. FR and MCD spectra of the heat treated glasses are shown to be very close to those of γ-Fe2O3 and practically independent of the RE element nature for the light wave energies lower than 22000 cm-1. For higher energies, the MCD spectrum shape depends strongly on RE what evidences the different origin of magneto-optical effects in two spectral ranges.

Vidros são materiais atraentes do ponto de vista científico e tecnológico, em especial porque algumas composições químicas permitem a fabricação em larga escala e/ou podem apresentar propriedades físico-químicas que os tornam candidatos promissores para aplicações como meio ativo para lasers, filtros ópticos, fibras ópticas, blindagens mecânicas ou como objeto de decoração ou utensílios domésticos ou como elemento para a construção civil, entre outras. Um dos desafios em preparar novas composições de materiais vítreos é garantir que não apareça o fenômeno da devitrificação. Este trabalho foi realizado com o objetivo de preparar e caracterizar uma nova matriz multicomponente, a base de óxido de boro, livre do fenômeno de cristalização. A matriz [50B2O3 - 15ZnO - 10PbO - 8MgO - 6K2O - 2Al2O3 - 2Nb2O5 - 5Si2O - 2Na2O] %wt pura e dopada com 0,1% mol de íons de metais de transição (MnO2, Fe2O3, CoO, NiO, CuO e CdCl2), foram preparadas em forno elétrico de atmosfera aberta usando cadinho de platina e caracterizadas usando as técnicas de: difração de raios X, análise térmica, densidade, pelo princípio de Arquimedes, microdureza Vickers, colorimetria, absorção óptica no intervalo ultravioleta-vísivel (UV-Vis) e transmissão óptica na região do infravermelho (FTIR). Resultados de difração de raios X confirmaram o caráter não cristalino das amostras vítreas. A adição de dopantes levou a mudança no número de coordenação na rede borato. Resultados de absorção óptica evidenciaram que a nova matriz desenvolvida com a adição de íons de metais de transição absorvem na região do visível e infravermelho próxima. Esses vidros tem potencial de aplicação na indústria de produtos decorativos e como filtros ópticos.
Glasses are attractive materials on a scientific and technologic point of view especially because some of their chemical compositions can provide a large scale production and/or may present physicochemical properties that them become promising candidates for applications as laser active environments, optical filters, optical fibers, mechanical shielding, adornment, domestic tools or construction stuff, among others. One of the challenges in preparing new compositions of glassy materials is to ensure that does not appear the phenomenon of devitrification. This work was carried out in order to prepare and characterize a new multicomponent glassy matrix, the basis of boron oxide, free from crystallization phenomenon. Pure glassy samples of [50B2O3 - 15ZnO - 10PbO - 8MgO - 6K2O - 2Al2O3 - 2Nb2O5 - 5Si2O - 2Na2O % wt] and 0.1% mol of transition metal ions (MnO2, Fe2O3, CoO, NiO, CuO e CdCl2) doped were prepared in open atmosphere electric furnace using platinum crucible and characterized using x-ray diffraction, thermal analysis, density evaluation from Archimedes principle, Vickers microhardness measurements, colorimetry, UV-VIS optical absorption and IR optical transmission. X-ray diffraction results confirmed non-crystalline character of the vitreous samples. Dopants addition led to changing on the coordination number of the borate network. Optical absorption results showed that the new glassy matrix developed with addition of transition metal ions absorb in the visible and near infrared range. These glasses may have potential applications in decorative products and as optical filters.

The increasing demand for energy and the necessity to overcome the depletion of fossil fuel supplies requires that alternative energy sources be developed. Solid Oxide Fuel Cells (SOFCs) are one of the alternative technologies to minimise our dependence on fossil fuel due to their numerous advantages including high efficiency, long-term stability, fuel flexibility and low emissions. However, the development of reliable sealing techniques remains a crucial challenge to overcome to allow usable efficiency and facilitate commercialization. Sealing technology has been object of research for several years. Nevertheless, the optimal solution is yet to be found. The use of a glass composite approach is attractive as it allows the possibility of engineering the properties of the seal, by independently adjusting the particle size distribution and volume fraction of the additives. In the present work, the interaction between various SiO2 based glasses with nickel and B2O3 based glasses with silver were studied. Results as a function of additive particle size distribution (7-100 microns) and volume fraction (0-18%) will be presented. Micrographs, X-ray patterns and CTE measurements showed that the proposed systems have adequate characteristics for usage as seal for fuel cells due to the inertness of the additive particles with the respective glass matrix and predictable long-term chemical and thermal stability. The use of DTMA as a technique to calculate the onset of residual stresses, explores the influence of the additive and its interfacial interactions on the dissipation of energy during deformation. The multi-frequency test lead to an activation energy for stress relaxation between 400 and 600 kJ/mol depending on the different additive content. Furthermore, the temperature difference between de Tg and the onset of residual stresses was calculated showing that increments on the additive content results on a larger temperature range that allows stress relaxation. The mechanical response under compression test was also investigated to identify the potential deformation of a stack during service. The results showed that the glass composites can experience large deformations during the entire service cycle and not only during the isothermal service hold. Moreover, the microstructure in terms of crystalline phase evolves with the test temperature and the applied force, showing an increase of the crystals volume fraction when either the temperature of the applied load increase. The microstructures showed that the additive is getting aligned during deformation, providing an increased resistance to compression against flow of the viscous glass composite. Finally the measurement of the residual stresses as function of cooling rate and additive content revealed that the residual stresses development is minimised for a combination of service conditions including cooling rate under 20 °C/min and glass composite containing a minimum of 12 %vol. Such operating conditions should contribute to maximise the service life of a SOFC stack.
La demande croissante en énergie et la nécessité de surmonter les défis d'épuisement des réserves de combustibles fossiles exigent que des sources d'énergies alternatives soient développées. Les piles à combustible à électrolyte solide sont l'une des technologies alternatives pour réduire notre dépendance aux combustibles fossiles en raison de leurs nombreux avantages, y compris leur haute efficacité, stabilité à long terme, flexibilité dans le choix du carburant et leurs faibles émissions. Cependant, le développement de techniques fiables pour joindre les composantes demeure un défi important à relever pour obtenir une efficacité utilisable et pour faciliter la commercialisation. Les technologies de jointage ont été l'objet de recherches depuis plusieurs années. Néanmoins, la solution optimale demeure encore à être trouvée. L'approche du composite de verre est intéressante car elle permet la possibilité d'optimiser les propriétés du joint en ajustant de façon indépendante la distribution de la taille des particules et la fraction volumique des additifs. Dans le présent travail, l'interaction entre des différents verres composites SiO2 avec nickel, et des verres composite B2O3 avec de l'argent ont été étudiés. Les résultats, en fonction de la distribution de la taille des particules (7-100 microns) et la fraction volumique des additifs (0-18%) seront présentés. Les micrographies, la diffraction des rayons X et les calculs du coefficient d'expansion thermique ont démontré que les systèmes proposés ont les caractéristiques adéquates pour leur utilisation en tant que joint pour les piles à combustible, en raison de l'inertie des particules d'additif avec la matrice de verre, et en raison de la prévisibilité à long terme de la stabilité chimique et thermique. L'utilisation de l'analyse thermomécanique dynamique comme technique pour calculer l'apparition de contraintes résiduelles, explore l'influence de l'additif et ses interactions relatives à l'égard de la dissipation de l'énergie pendant la déformation. Les tests à multifréquences a mené à une énergie d'activation variant entre 400 et 600 kJ/mole pour la relaxation des contraintes, er ce en fonction des différentes quantités d'additifs. De plus, la différence de température entre Tg et l'apparition de contraintes résiduelles a été calculée, et démontre que des incréments de quantités d'additif résultent en un augmentation de l'interval de températures pouvant permettre la relaxation des contraintes. Les résultats du point de vue mécanique, pour des tests de compression ont également été étudiés afin d'identifier les déformations potentielles des assemblages durant l'opération. Les résultats ont montré que les composites de verre peuvent subir de grandes déformations au cours du cycle entier d'opération et non pas seulement pendant la période isotherme. De plus, la microstructure, en termes de phases cristallines, évolue avec la température d'essai et la force appliquée, montrant une augmentation de la fraction volumique des cristaux avec l'augmentation de la température et de la charge appliquée. Les microstructures ont démontré que les particules s'alignent pendant la déformation, offrant une résistance accrue contre la compression, résultant de l'écoulement du composite de verre visqueux. Enfin, le calcul des contraintes résiduelles en fonction de la vitesse de refroidissement et de la fraction volumique d'additifs a révélé que le développement des contraintes résiduel est minimisé dans quelques combinaisons de conditions d'opération, incluant un taux de refroidissement en dessous de 20 °C/min et une fraction volumique minimum de 12% en additif. Ces conditions d'opérations devraient contribuer à maximiser la durée de vie des assemblages de piles à combustible à électrolyte solide.

Ce travail est consacre a l'etude et a la modelisation de l'echange ionique ag#+/na#+ dans des verres a base d'oxydes. Il s'inscrit dans un cadre plus large visant a une meilleure comprehension des mecanismes presidant a la fabrication des guides d'onde. Nous avons synthetise et caracterise des borates et des silicates de sodium et d'argent. L'etude de leurs proprietes electriques a mis en evidence un phenomene se traduisant par des variations non lineaires de la conductivite electrique avec le taux de substitution du sodium par l'argent dans ces materiaux, et connu sous l'appellation effet de cation mixte ag#+/na#+. Nous avons egalement elabore un modele capable de decrire le processus de l'echange ionique. Il presente la particularite de prendre en compte l'effet de cation mixte apparaissant dans le materiau lors de l'echange. Pour cela, nous avons choisi une loi de variation non lineaire des coefficients de diffusion des cations mobiles en fonction de leur teneur dans le verre. Enfin, nous avons procede a des echanges ag#+/na#+ par oxydation electrochimique de films metalliques d'argent deposes sur des echantillons de silicate et de borate de sodium. Les differents profils ont ete determines par des methodes optique (indice de refraction) ou physicochimique (concentration), et sont en bon accord. La correlation entre les resultats experimentaux et ceux issus de la simulation est satisfaisante. Des ameliorations sensibles peuvent etre encore apportees, tant du point de vue de la realisation des materiaux a gradient d'indice, que du modele de l'echange ionique

Transparent glasses embedded with ferroelectric/nonlinear optic crystallites have been in increasing demand as these exhibit promising physical properties. These could be fabricated in large sizes and shapes with high optical homogeneity accompanied by high degree of transparency over a wide range of wavelengths of light. Amongst a variety of glasses that are known, borate-based glasses are of particular interest owing to their greater transparency, good chemical and mechanical stability, low materials cost, and useful electrical and dielectric properties. Keeping the potential multifarious applications of transparent glass-microcrystal composites in view, BaO-0.5Na2O-4.5B2O3, BaO-0.5Li2O-4.5B2O3, SrO-0.5Li2O-4.5B2O3, 3BaO-3TiO2-B2O3 and Li2O-3B2O3 glasses and glass-microcrystal composites were fabricated. These glasses on controlled heat treatment at appropriate temperatures yielded BaNaB9O15, BaLiB9O15, SrLiB9O15, Ba3Ti3B2O12 and LiB3O5 crystalline phases, respectively. Further transparent surface crystallized BaO-0.5Na2O-4.5B2O3 glasses were fabricated using ultrasonic treatment and their thermal properties have been investigated in detail using differential scanning calorimetry. It is observed that these glasses were homogeneously crystallizing on the surfaces after Ultrasonic treatment which can be exploited for planner wave-guide applications. Glass forming ability, thermal stability, glass-transition behavior, crystallization kinetics and viscosity of these glasses were studied extensively using various methods and rationalized by invoking various models. The above glasses have been characterized for their dielectric and electrical relaxation properties (as these properties are related to their electro-optic and non-linear optical properties) over 30- 600oC temperature range and frequencies (100 Hz -10 MHz) that are normally of interest in the applications of these materials. Several interesting features such as high ionic conductivity, marginally low dielectric loss and high dielectric constant behavior along with low thermal coefficient of dielectric constant were observed in these glasses and were rationalized using various models. The combination of these dielectric characteristics suggests that these are potential candidates for electrical energy storage device applications.

Transparent glasses embedded with ferroelectric/nonlinear optic crystallites have been in increasing demand as these exhibit promising physical properties. These could be fabricated in large sizes and shapes with high optical homogeneity accompanied by high degree of transparency over a wide range of wavelengths of light. Amongst a variety of glasses that are known, borate-based glasses are of particular interest owing to their greater transparency, good chemical and mechanical stability, low materials cost, and useful electrical and dielectric properties. Keeping the potential multifarious applications of transparent glass-microcrystal composites in view, BaO-0.5Na2O-4.5B2O3, BaO-0.5Li2O-4.5B2O3, SrO-0.5Li2O-4.5B2O3, 3BaO-3TiO2-B2O3 and Li2O-3B2O3 glasses and glass-microcrystal composites were fabricated. These glasses on controlled heat treatment at appropriate temperatures yielded BaNaB9O15, BaLiB9O15, SrLiB9O15, Ba3Ti3B2O12 and LiB3O5 crystalline phases, respectively. Further transparent surface crystallized BaO-0.5Na2O-4.5B2O3 glasses were fabricated using ultrasonic treatment and their thermal properties have been investigated in detail using differential scanning calorimetry. It is observed that these glasses were homogeneously crystallizing on the surfaces after Ultrasonic treatment which can be exploited for planner wave-guide applications. Glass forming ability, thermal stability, glass-transition behavior, crystallization kinetics and viscosity of these glasses were studied extensively using various methods and rationalized by invoking various models. The above glasses have been characterized for their dielectric and electrical relaxation properties (as these properties are related to their electro-optic and non-linear optical properties) over 30- 600oC temperature range and frequencies (100 Hz -10 MHz) that are normally of interest in the applications of these materials. Several interesting features such as high ionic conductivity, marginally low dielectric loss and high dielectric constant behavior along with low thermal coefficient of dielectric constant were observed in these glasses and were rationalized using various models. The combination of these dielectric characteristics suggests that these are potential candidates for electrical energy storage device applications.

Transparent glasses embedded with TTB structured ferroelectric nano/micro crystals (K3Li2Nb5O15, Ba5Li2Ti2Nb8O30) were fabricated in various tellurite and borate based glass matrices and characterized for their physical properties. Nanocrystals of K3Li2Nb5O15 were successfully grown inside tellurite glass matrix via conventional heat-treatment route. Eventhough, tellurite glasses preferentially crystallize only on the surface, bulk uniform crystallization was achieved in the (100-x) TeO2 - x(1.5K2O-Li2O-2.5Nb2O5) system. Heat capacity studies revealed them to be thermodynamically less fragile than any other tellurite glasses ever reported in the literature. Pyroelectric and ferroelectric effects as well as second harmonic generation were demonstrated for the heat treated (glass nanocrystal composites) samples in this system. The conventional method of melt-quenching of constituent oxides could not yield Ba5Li2Ti2Nb8O30 crystallites. So, Ba5Li2Ti2Nb8O30 microcrystals were successfully formed in tellurite glass matrix by mixing pre-reacted Ba5Li2Ti2Nb8O30 ceramic powders with TeO2. The glass transition temperature was found to be the highest ever reported and this system was kinetically strong based on the fragility parameter. Dielectric studies revealed a frequency and temperature independent nature of the dielectric constant and very low dielectric loss. The SHG measurement which was carried out as a function of temperature demonstrated the incidence of blue second harmonic generation in the microcrystals present in the glass matrix. Ba5Li2Ti2Nb8O30 nanocrystals were successfully crystallized in the transparent glass system (100-x)Li2B4O7 – x(Ba5Li2Ti2Nb8O30). Dielectric constant increased while the dielectric loss decreased with the increase in Ba5Li2Ti2Nb8O30 content. Nuclear magnetic resonance spectroscopic studies were carried out to have an insight into the structure of this system. Transmission studies and refractive index measurements were performed and various optical parameters were calculated. Dielectric and transport properties were studied for the glasses and glass nano/microcrystal composites of all the systems reported in this thesis. Li+ ion was found to be responsible for conduction in all these systems. Evolution of self-organized nanopatterns of K3Li2Nb5O15 crystals has been demonstrated in the glass system (100-x) TeO2 - x(1.5K2O-Li2O-2.5Nb2O5) by excimer laser irradiation. The second harmonic signal observed by the Maker fringe technique has been attributed to the presence of well-aligned nano-sized grating structures in the glass system. Glasses belonging to the systems TeO2-K3Li2Nb5O15, TeO2-Ba5Li2Ti2Nb8O30 and V2Te2O9 undergo spinodal decomposition on exposing to KrF pulsed excimer laser. The spinodally phase separated structures were observed on all the surfaces of the samples. Ring shaped patterns were observed on several locations of the samples at higher frequency of laser pulses probably owing to the shock waves produced by the high intense laser beam. Line shaped patterns were found to originate on the sample surfaces when irradiated for longer periods.

Transparent glasses embedded with TTB structured ferroelectric nano/micro crystals (K3Li2Nb5O15, Ba5Li2Ti2Nb8O30) were fabricated in various tellurite and borate based glass matrices and characterized for their physical properties. Nanocrystals of K3Li2Nb5O15 were successfully grown inside tellurite glass matrix via conventional heat-treatment route. Eventhough, tellurite glasses preferentially crystallize only on the surface, bulk uniform crystallization was achieved in the (100-x) TeO2 - x(1.5K2O-Li2O-2.5Nb2O5) system. Heat capacity studies revealed them to be thermodynamically less fragile than any other tellurite glasses ever reported in the literature. Pyroelectric and ferroelectric effects as well as second harmonic generation were demonstrated for the heat treated (glass nanocrystal composites) samples in this system. The conventional method of melt-quenching of constituent oxides could not yield Ba5Li2Ti2Nb8O30 crystallites. So, Ba5Li2Ti2Nb8O30 microcrystals were successfully formed in tellurite glass matrix by mixing pre-reacted Ba5Li2Ti2Nb8O30 ceramic powders with TeO2. The glass transition temperature was found to be the highest ever reported and this system was kinetically strong based on the fragility parameter. Dielectric studies revealed a frequency and temperature independent nature of the dielectric constant and very low dielectric loss. The SHG measurement which was carried out as a function of temperature demonstrated the incidence of blue second harmonic generation in the microcrystals present in the glass matrix. Ba5Li2Ti2Nb8O30 nanocrystals were successfully crystallized in the transparent glass system (100-x)Li2B4O7 – x(Ba5Li2Ti2Nb8O30). Dielectric constant increased while the dielectric loss decreased with the increase in Ba5Li2Ti2Nb8O30 content. Nuclear magnetic resonance spectroscopic studies were carried out to have an insight into the structure of this system. Transmission studies and refractive index measurements were performed and various optical parameters were calculated. Dielectric and transport properties were studied for the glasses and glass nano/microcrystal composites of all the systems reported in this thesis. Li+ ion was found to be responsible for conduction in all these systems. Evolution of self-organized nanopatterns of K3Li2Nb5O15 crystals has been demonstrated in the glass system (100-x) TeO2 - x(1.5K2O-Li2O-2.5Nb2O5) by excimer laser irradiation. The second harmonic signal observed by the Maker fringe technique has been attributed to the presence of well-aligned nano-sized grating structures in the glass system. Glasses belonging to the systems TeO2-K3Li2Nb5O15, TeO2-Ba5Li2Ti2Nb8O30 and V2Te2O9 undergo spinodal decomposition on exposing to KrF pulsed excimer laser. The spinodally phase separated structures were observed on all the surfaces of the samples. Ring shaped patterns were observed on several locations of the samples at higher frequency of laser pulses probably owing to the shock waves produced by the high intense laser beam. Line shaped patterns were found to originate on the sample surfaces when irradiated for longer periods.

The physical properties of borate-based glasses comprising crystallites of inorganic materials (polar) at different length scales have become increasingly important owing to their importance in the design and fabrication of composites for multifarious applications. Though ceramics of polar materials meet industrial demands to a great extent, they suffer from higher levels of porosity accompanied by grain boundary related problems which affect their physical properties. One of the diligent ways to circumvent this problem would be to adopt technologically viable alternate routes to fabricate ceramics. Among many others, glass-ceramic route could be effectively used to fabricate nearly pore-free structured ceramics. Indeed, this route provides with greater flexibility to obtain glasses with varied crystallite sizes via devitrification process at appropriate temperatures and duration of heat-treatment. Glass nanocrystal composites (GNC) form a subset of well-known class of materials, glass-ceramics. Therefore, it was in order, to disperse/embed nano crystallites of polar materials in appropriate glass matrices and visualize their physical properties that were of prime academic/technological interest. Barium sodium niobate (BNN) has a filled tungsten bronze structure associated with the general formula (A1)2(A2)4(C)4(B1)2(B2)8O30. It is known to be an interesting material especially from its electro-optic and non-linear optic properties viewpoint. Since growing single crystals of the desired size and shape of BNN is cumbersome, we thought that it was worth attempting to obtain equally transparent (optically) glasses containing nano/micro crystallites of BNN and visualize their physical properties while we are well aware that these properties would be inferior to that of their single crystalline counterparts. However, the challenge lies in tailoring glass nanocrystal composites with the desired microstructures for specific applications. In the present investigations refractive index and band gap tunability have been accomplished by exercising a strict control over the crystallite sizes of Barium Sodium Niobate (BNN) in borate glass matrix. The frequency and temperature independent dielectric characteristics were demonstrated over a wide range of frequencies and temperatures. An attempt has been made to understand the origin of intense photoluminescence exhibited by these samples particularly at nanoscale. White light emitting phosphor materials have been fabricated by doping Barium Sodium Niobate (Ba2NaNb5O15) ceramics with Er3+. Strontium equivalent i.e. Sr2NaNb5O15 to BNN associated with improved piezo properties has been synthesized by adding MnO2 as a sintering aid. An attempt has been made to understand the origin of relaxor behavior of tetragonal tungsten bronze family of oxides. The results that are obtained in the present investigations have been classified into the following chapters. Each chapter is provided with conclusions and a list of references. Chapter 1 gives a brief exposure to the tetragonal tungsten bronze structured materials. The emphasis has been on the optical, dielectric, ferroelectric and piezoelectric applications of these materials. A preamble to glasses, thermodynamic aspects of glass formation and fabrication of glass-ceramics are also included. The origin of photoluminescence in nano structured materials besides the tunability of their optical properties are included. Chapter 2 deals with the detailed description concerning various experimental techniques that are employed to synthesize and characterize the materials under investigations. Chapter 3 includes the details about the evolution of nanocrystalline Ba2NaNb5O15 phase in 2BaO-0.5Na2O-2.5Nb2O5-4.5B2O3 glass system and its refractive index and band gap tunability. Monophasic Ba2NaNb5O15 was crystallized at nanometer scale (12-36 nm) in 2BaO-0.5Na2O-2.5Nb2O5-4.5B2O3 glass system. To begin with, optically transparent glasses in this system were fabricated via the conventional melt- quenching technique. The amorphous and glassy characteristics of the as-quenched samples were respectively confirmed by X-ray powder diffraction and differential thermal analyses. Nearly homogenous distribution of Ba2NaNb5O15 (BNN) nanocrystals associated with tungsten bronze structure akin to their bulk parent structure was accomplished by subjecting the as-fabricated glasses to appropriate heat-treatment temperatures. Indeed, Transmission Electron Microscopy (TEM) carried out on these samples corroborated the presence of BNN nanocrystals dispersed in a continuous glass matrix. The as-quenched glasses were ~75% transparent in the visible range of the electromagnetic spectrum. The optical band gap and refractive index were found to have strong crystallite size (at nano scale) dependence. The optical band gap increased with the decrease in crystallite size. The refractive indices of the glass nanocrystal composites as determined by Brewster angle method were rationalized using different empirical models. The refractive index dispersion with wavelength of light was analyzed by invoking the Sell Meier relations. At room temperature under UV excitation (355 nm), these glass nanocrystal composites displayed violet-blue emission which was ascribed to the presence of defect states. Chapter 4 comprises the temperature (300-973 K) and frequency (100 Hz-10 MHz) response of the dielectric and impedance characteristics of 2BaO-0.5Na2O-2.5Nb2O5- 4.5B2O3 glasses and glass nanocrystal composites that were studied. The dielectric constant of the glass was found to be almost independent of frequency (100 Hz-10 MHz) and temperature (300-600 K). The temperature coefficient of dielectric constant was 8±3 ppm/K in the 300-600 K temperature range. The relaxation and conduction phenomena were rationalized using modulus formalism and universal AC conductivity exponential power law respectively. The observed relaxation behavior was found to be thermally activated. The complex impedance data were fitted using the least square method. Dispersion of Barium Sodium Niobate (BNN) phase at nanometer scale in a glass matrix resulted in the formation of space charge around crystal-glass interface, leading to a high value of effective dielectric constant especially for the samples heat-treated at higher temperatures. 7ªe fabricated glass nanocrystal composites exhibited P vs. E hysteresis loops at room temperature and the remnant polarization (Pr) increased with the increase in crystallite size. Chapter 5 describes the synthesis of fine powders comprising nano crystallites of barium sodium niobate, Ba2NaNb5O15 (BNN) via citrate assisted sol-gel route at much lower temperature than that of conventional solid-state reaction route. The phase evolution of BNN as a function of temperature was investigated by thermo gravimetric analysis (TGA), differential thermal analysis (DTA), Fourier transform infrared spectroscopy (FTIR) and X-ray powder diffraction (XRD). DTA data followed by XRD studies confirmed the BNN formation temperature to be around 923 K. The as-synthesized powders heat-treated at 923 K/10h attained orthorhombic structure akin to that of parent BNN phase. Transmission Electron Microscopy revealed the presence of dislocations in nano crystallites. The optical band gap was calculated using Kubelka-Munk function. These nano crystallites exhibited strong visible photoluminescence (PL) at room temperature. The PL mechanism was explained by invoking the dielectric confinement effect, defect states and generation of self-trapped excitons. Chapter 6 illustrates the synthesis of Erbium (Er3+) doped nanocrystalline barium sodium niobate (Ba2Na1-3xErxNb5O15 where x=0, 0.02, 0.04 and 0.06) via citrate-based sol-gel route. The desired phase formation was confirmed by X-ray powder diffraction followed by FT-IR studies. The high-resolution transmission electron microscopy facilitated the establishment of the structure of nano crystallites and their morphology. Kubelka-Munk function was employed to obtain the optical band-gap based on diffused reflectance studies carried out on nano sized crystallites. The synthesized samples (x=0.02, heat-treated at 1023 K/2h) exhibited room temperature white light (blue, red and green) emission at a CIE coordinate (0.34, 0.40) and a color temperature ~5280 K, (cool white) under the excitation radiation of 355 nm. The blue (408 nm), green (524, 547 nm) and red (672 nm) emission bands were having their origin in Er3+-ions. Chapter 7 deals with the fabrication of high temperature lead-free ferroelectric ceramics (Sr2NaNb5O15 + x wt% MnO2 (SNN-x Mn)) by conventional solid-state reaction route. Effects of MnO2 addition on the microstructure and electrical properties of Sr2NaNb5O15 ceramics were investigated for different x values (0≤x≤0.5). The microstructural, dielectric, ferroelectric and piezoelectric properties were studied. The MnO2-added SNN based ceramics were found to have tetragonal tungsten bronze structure at room temperature. Nearly equiaxed grains were obtained and the grains became larger with the increase of MnO2 addition up to x=0.25. The Curie temperature TC was found to increase with the increase of MnO2 addition besides an enhancement in the dielectric, Polarization vs. Electric field (P–E hysteresis loop) and strain vs. electric field characteristics. For instance, improved polarization performance (2Pr =10.78 C/cm2 and 2Ec of 28.06 kV/cm) was obtained for the SNN-0.25 wt% MnO2 added ceramics. It was apparent that the MnO2 added SNN ceramics could show restrained cracks and enhanced piezoelectric properties. These results indicate that the SNN–x Mn ceramics (as lead-free piezoceramics) are promising for piezoelectric based device applications. The details pertaining to the synthesis and fabrication of high-density tungsten bronze Sr2NaNb5-yTayO15 (0≤y≤1.5) ceramics are also reported in this chapter. The effects of Ta5+ substitution on the microstructure and physical properties of the ceramics were systematically investigated. The XRD analyses revealed a decrease in lattice parameter on increasing Ta5+ substitution level. With the increasing of Ta5+ substitution, the orthorhombic– tetragonal transition temperature TO−T and the Curie temperature TC decreased monotonically. For the ceramics corresponding to y=1.5 the Curie temperature was found to be 273 K, i.e. the material is paraelectric at room temperature. Under systematic optimization of the substitution level, improved overall electrical properties i.e. d33=71 pC/N, S=0.033%, TC= 503 K, 2Pr=11.96 C/cm2 and 2Ec=28.55 kV/cm were obtained for ceramics corresponding to the composition y (Ta5+)=0.05. The thesis ends with an overall summary and conclusions followed by the vistas ahead.

Boron compounds are beneficial additives for industrial applications due to their superior physical, chemical, mechanical, and thermal features. The common use of boron compounds can be listed as ceramic, glass, glazes, metallurgy, lubricating agents, non-linear optical devices, and nuclear processes. Metal borates can be classified in accordance with the metal atom in the structure. According to the metal borate type, each compound exhibits different properties and is preferred for various applications. The other significant factor of a material that makes it preferable for the industry is its morphological characteristics. With the developing technology and novel synthesis procedures, metal borates can be fabricated at different morphologies. The characteristics of the metal borates can be improved by the modification of their surfaces. Capping agents are additive materials that are used to control particle growth and/or modify the morphological features of compounds. There is a recent increase in the number of studies based on metal borates prepared by using capping agents. In this chapter, the theoretical background on metal borates, synthesis procedures of metal borates, classification of the capping agent, the effect of capping agent on particle growth and examples of capping agent use on metal borates preparation were explained. Also, the characteristics of the same metal borates at different morphological features were compared.

Recently, the interests in optical memory based on persistent spectral hole burning (PSHB) are increased because of its possibility of the application to high density optical memory. PSHB was observed for an organic dye doped in polymer and rear earth or transition metal doped in inorganic crystal or glasses up to now. Since PSHB was observed by two Russian groups (Gorokhovskii et al. and Kharlamov et al.) for free base phthalocyanine in a n-octane Shpol'skii matrix1 and for perylene and 9-aminoacridine molecules in glassy ethanol matrix2, PSHB materials are studied primarily for the polymer doped with an organic dye. But such materials can make hole only at very low temperature. Room temperature PSHB phenomena were observed on Sm2+ doped fluoride crystals3-5 and glasses6 recently, however these materials' Гih(inhomogeneous line width)/Гh(homogeneous line width)'s which are the parameters of data multiplicity in PSHB optical memory are an order of unity. For the application of PSHB materials to optical memory, high operating temperature, high Гih/Гh, and rapid reaction rate are wanted. Glass has a superiority on the view point of optical memory application because of its broad inhomogeneous line width and productivity. Our group has discovered room temperature PSHB for Sm2+ in borate glass systems whose Гih/Гh is 24.7 PSHB for rear earth metal in glass matrix has not been studied seriously, yet. It is thought that the study of the relationship between the optical hole and glass structure is necessary.

One issue when utilizing natural oils as raw materials for preparing polymers in comparison with petrochemical starting materials is their complexity. Standard natural oils have typically very heterogeneous structure, which is reflected on properties of polymers. However, oils with regular structure such as high oleic oils, offer high degree of regularity approaching that of triolein. Cationic polymerization of epoxidized oils was carried in bulk using tris (pentafuorophenyl)borane. Epoxy resin made solely from epoxidized soybean oil (ESO) was compared with that from epoxidized high oleic algal (ETO) containing over 90 % oleic acid, with triolein as major component. Although epoxidized soybean oil had higher functionality (EOC content), the obtained algal epoxy resin displayed higher glass transition temperature than soybean resin’s. The possible reasons are high oleic algal oil has higher regularity and soybean oil contains high content of saturated fatty acid (15 %), which can act as plasticizer. Moreover, crosslinking in ESBO might involved formation of cyclics from neighboring epoxy groups present in epoxidized linoleic acid and higher local cross-linking density.