Academic literature on the topic 'Potassium Lithium Niobate'

The use of lithium niobate and liquid crystals in solar instrumentation designed for automatic measurement of spectral line shifts is described. A solid Fabry-Perot etalon of lithium niobate has an acceptance angle 5�3 times greater than an air-spaced Fabry-Perot filter for the same allowed passband broadening, and the lithium niobate device has no moving parts. The use of liquid crystals in Zeeman-effect analysers is also described. For a given phase retardation, liquid crystals require -1/1000 the voltage of solid crystals. They hold promise as reliable, long-lived variable retarders because they are free of the high-voltage breakdown problems of crystals such as potassium dideuterium phosphate (KDP). Progress toward implementation of devices with lithium niobate and liquid crystals in a solar telescope is described.

The present work reports the effect of lamination of biocompatible lithium sodium potassium niobate multilayered tapes between hydroxyapatite (HA) layers on the dielectric and electrical properties of HA.

Results of studying the domain structure of planar Ni microparticles formed on single-crystal substrates from the lithium niobate and from the potassium titanyl phosphate at different temperatures are presented. The dependence of domain sizes on the sample temperature was studied. It is shown the observed change of the domain structure is caused by the magnetoelastic effect, which arises due to the difference in the thermal expansion coefficients of the substrate and microparticles as the sample temperature changes. It is shown, the sizes of magnetic domains, up to the creation of a state with a quasi-homogeneous magnetization may be set by the substrate temperature during the microparticles formation. Keywords: magnetoelastic effect, magnetic force microscopy, remagnetization, lithium niobate, potassium titanyl phosphate, temperature.

Nous avons etudie par topographie aux rayons x, en utilisant principalement le rayonnement synchrotron, des monocristaux sous champ electrique tels que la forme alpha de l'iodate de lithium (-liio#3), l'orthophosphate potassium titanyl (ktp=ktiopo#4) et le niobate de lithium (linbo#3). Ces etudes ont ete menees dans le but d'elucider les mecanismes de formation des gradients de distorsion sous champ. Nous avons observe sur les topographies les effets qui se produisent sur les cristaux de -liio#3 et ktp lorsqu'un champ electrique est applique suivant l'axe c. Les resultats nouveaux, surtout les mesures en courant alternatif et les experiences a basse temperature, ont montre que la conductivite ionique unidimensionnelle n'est pas un phenomene preponderant a la base des lignes paralleles a l'axe c observees sous champ, comme cela a ete suppose jusqu'a present. Ceci nous a permis de remettre en cause les modeles mentionnes dans la litterature, et de proposer notre modele des canaux polarises. Sur les cristaux de linbo#3 (et -liio#3) implantes par l'hydrogene nous avons observe, sur les topographies en section, la couche associee a l'implantation. Les experiences ont montre que la couche implantee est monocristalline, legerement desorientee par rapport au volume, observable sans champ. Sous champ, elle n'est pas visible. Par contre, la couche traversee par les ions implantes est, sous champ, a l'origine de l'observation d'une ligne parallele a la surface, plus desorientee par rapport au volume que la couche implantee sans champ. La desorientation de cette image de la zone traversee semble etre fortement correlee avec l'effet piezoelectrique. Nous proposons deux hypotheses qui pourraient expliquer ce phenomene

Les propriétés physiques de deux types de cristaux construits sur le motif commun: l'octaèdre NbO6, un cristal à structure bronze de tungstène K6Li4Nb10O30 (KLN) et l'autre à structure pérovskite AgNb(x)Ta(1-x)O3 (ATN), ont été étudiées expérimentalement et théoriquement. Dans la section A, une étude par spectroscopie Raman et par génération de seconde harmonique effectuée sur des cristaux de type KLN, a permis de mettre en place un procédé de caractérisation non destructive du degré de non-stœchiométrie de nos échantillons: cela pour l'utilisation d'une relation entre la fréquence caractéristique d'un mode Raman et l'excès de niobium dans le cristal. L'étude par spectroscopie Raman a également mis en évidence une éventuelle présence d'un mode mou sur-amorti visible lors de la transition de phase ferroélectrique-paraélectrique. D'autre part les concentrations en Nb de nos échantillons ont été validés par une étude de l'accord de phase non-colinéaire lors de mesures de génération de seconde harmonique. Dans la section B de ce mémoire, nous avons analysé les propriétés dynamiques d'un composé de la famille des pérovskites: AgNb(x)Ta(1-x)O3 (ATN). Une étude (en collaboration avec des laboratoires russes, lithuaniens et polonais) de la réponse diélectrique de ce système, sur une très vaste gamme de fréquence (1 MHz - 30 THz) a mis en évidence l'existence d'une dispersion diélectrique haute fréquence (vers 0. 5 THz, située en dessous des dispersions phononiques), à caractère relaxationnel, due aux ions Nb5+. Ce fait a été validé par le test de deux types de fonctions réponse permettant de décrire de façon cohérente la transition de phase M2-M3 du système ATN. Le contrôle précis du taux de substitution de l'ion Nb5+ par Ta5+ permet d'ajuster la permittivité diélectrique entre 100 et 700 avec une grande stabilité et sans pertes dans une grande gamme de fréquence de 1 MHz à 100 GHz. Enfin, dans la section C, une réflexion plus générale sur les origines du comportement et de la nature des transitions de phase des cristaux à structure pérovskite et tungstène-bronze, ainsi que sur celles des non-linéarités est réalisée. Le rôle primordial de l'octaèdre NbO6, d'une éventuelle substitution du Nb5+ par des ions Ta5+, et de son environnement a été mis en évidence sur la base des résultats des sections A et B, et de données de la littérature
The physical properties of the tungsten bronze compound K6Li4Nb10O30 (KLN) and the perovskite compound AgNb(x)Ta(1-x)O3 (ATN), based on the common NbO6 octahedra, were studied theoretically and experimentally. These two families are intensively studied for their strong optical non linearities, suitable for laser beams generation and processing. In section A, a non destructive characterisation process of Nb excess in our samples was performed. It was based on a Raman spectroscopy study and a second harmonic generation study on KLN crystals, A correlation between the frequency of a characteristic mode and Nb excess was evidenced. The Raman spectroscopy study pointed out the possible presence of an overdamped soft mode near the ferroelectric-paraelectric phase transition. Moreover, the Nb concentration of our samples was confirmed by a non collinear phase matching study in SHG experiments. Owing to the extraordinary refraction index strong dependence on Nb concentration, a non critical phase matching can be performed by choosing the Nb content. The KLN system seems to be a promising material for frequency doubling integrated wave guides. In section B of the thesis, the dynamical properties of the perovskite compound AgNb(x)Ta(1-x)O3 (ATN) were analysed. Thanks to a collaboration with Russian (Moscow), Lithuanian (Vilnius) and polish (Katowice) laboratories, a study of the dielectric response of this system, on a broad frequency range ((1 MHz - 30 THz), evidenced the following facts : a high frequency (0. 5 THz) dielectric dispersion occurs, the dispersion exhibits a relaxational nature involving the Nb5+ ions. This dispersion was described by two kinds of response functions. , the control of Nb/Ta substitution can be used to set dielectric permittivity from 100 to 700 without losses in the 1 MHz - 100 GHz range, making ATN compound very interesting for high frequency dielectric devices. At last, in section C, a general discussion on the physical origins of the phase transitions and optical non linearities in the tungsten bronze and the perovskite compounds is presented. The role of NbO6 octahedra on these properties has been evidenced on the basis of the results of sections A and B, and on literature data

This thesis describes the physical and photorefractive properties of potassium lithium tantalate niobate (KLTN) single crystal material. The top seeded solution growth method is reviewed. The phase transition temperatures and dielectric properties are related to the compositions of the KLTN crystals. A liquid/solid interface dynamics model is introduced to explain the experimental results which is that hydrogen ion concentration in KLTN crystals can be reduced dramatically by doping copper in the absence of titanium. Dark conductivity of KLTN crystals are contributed by two species when the temperature is in the range of 250 K and 350 K. Two species are hydrogen ions and shallow trapped electrons (holes). These results have been confirmed by direct dc conductivity measurements and holograms fixing experiments. Hydrogen ion has two types of motion in the crystals: O-H vibration and O-H libration. We established a model to describe hydrogen ions motions and hopping in KLTN crystals. The theoretical prediction is in agreement with experimental results. Hologram thermal fixing for optical data storage is discussed. Hydrogen ions are identified as the mobile ion which is responsible for thermal fixing. In ferroelectric phase KLTN crystals, spontaneous polarization of individual microdomains can be aligned throughout the entire crystal by the poling process. Photorefractive space charge fields play a role deploing the microdomains wherever space charge field opposing to spontaneous polarization. This may cause microdomain switching and lead to the generation of index grating. Experimental observation of Barkhausen current jumps is the signature of domain inversion. Holograms thermal fixing in potassium niobate crystals are also investigated. Because potassium niobate crystal has an orthognal structure with space group mm2, 3D polarization dependence of OH bands are observed. A special cut of iron doped potassium niobate crystal was designed to achieve the maximum exponential gain coefficient for thermal fixing of volume holograms. A significant enhancement of diffraction efficiency of the fixed grating 43% is measured. The last part of this thesis discussed topological distribution of phase matching of three-wave mixing in biaxial crystals. Thirty possible distributions are illustrated. The optimum operating directions under phase matching condition in biaxial crystal can be obtained from the calculation of the effective nonlinear coefficients. A set of analytical expressions of effective nonlinear optical coefficient for the crystals with mm2 point group is given. The phase matching directions are in either x, y, or z plane in order to obtain maximum coefficient.

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. This thesis describes the growth of photorefractive potassium lithium tantalate niobate (KLTN) single crystal material and characterization of its physical and photorefractive properties. The band transport model is used to discuss the conventional photorefractive effect. The coupled mode formalism is introduced to determine the interaction of interfering light beams in a photorefractive material. Solutions for intensity coupling and phase coupling between two beams, as well as diffraction off a dynamic index grating, are presented for both the copropagating and counterpropagating experimental geometries. These solutions are obtained for arbitrary photorefractive phase, [...]. The linear- and quadratic electro-optic effects are discussed. The influence of electric field application on the electro-optic tensor is described. The top seeded solution growth method is reviewed. The design and construction of a crystal growth system is described. The growth procedures of KLTN are enumerated for several compositions and dopant types. Phase diagrams of the KLTN system are determined. Structural properties of the grown crystals are presented. Certain material characteristics of KLTN are discussed. These include the phase transition temperatures, dielectric properties, and the optical absorption properties. Electric field control of the photorefractive effect, beam coupling and diffraction, is demonstrated for paraelectric KLTN. A theory is developed to describe the diffraction of beams off photorefractive index gratings in paraelectric KLTN. The solutions of the coupled mode equations are used to develop methods of determining the photorefractive phase [...] in a photorefractive material. These methods are experimentally demonstrated for several types of photorefractive material. In addition, they are used to corroborate a theory describing the magnitude and phase of the net holographic grating in paraelectric KLTN under applied electric field. A new effect, the Zero External Field Photorefractive (ZEFPR) effect is studied, as well as the application of its unique zero phase ([...] = 0) photorefractive gratings. The ZEFPR effect is forbidden by the conventional photorefractive theory; its origin is shown to be due to the creation of strain gratings under spatially periodic illumination. A theory of coordination of microscopic strains by a macroscopic (growth induced) strain is presented. The ZEFPR gratings are shown to possess identically zero phase when no external electric field is applied. This property is employed in the implementation of various new linear phase-to-intensity transduction devices. In particular, an all-optical phase modulation/vibration sensor (microphone) is described. This device is expected to have numerous applications in environments where electric fields cannot be permitted. The possible implementation of ZEFPR gratings in high speed self aligning interferometric data links is discussed, as well as implementation of a novel self aligning holographic image subtraction device. The final chapter is devoted to the solution of beam coupling and diffraction off of a "fixed" photorefractively written holographic plane grating. The solutions and mathematical tools developed in this chapter are used extensively throughout the thesis: in chapters two and five to describe diffraction off a photorefractive grating, in chapters seven and eight to solve for the beam coupling off a grating when one beam is phase modulated, and in chapter nine to study the spectral response of fixed holographic interference filters. The techniques are presented with sufficient generality to allow application to numerous other problems, not limited to the ones described here.

The present Thesis explores a few novel anode materials for both lithium-ion and sodium-ion rechargeable batteries. A series of layered metal titanium niobates have been synthesised and their electrochemical energy storage properties, ion transport, and reaction mechanisms are studied in detail. Alkali-titanium niobates such as Li-Ti-niobate (and it’s sodium counterpart) store lithium (sodium) via the conventional intercalation mechanism. Detailed experimental and theoretical investigations reveal interesting and non trivial ion transport, which are found to be strongly correlated to the electrochemical properties. Apart from intercalation, where amount of energy storage is limited by the crystal structure, energy storage via an alloying reaction is an important alternative strategy to boost specific capacities and energy densities of various battery systems. However, drastic volume changes during alloying/dealloying is detrimental for stable electrochemical function of the cell. The volume expansion problem associated with alloying anodes materials e.g. Sn for alkali-ion batteries have been tackled here via two different strategies. While one uses a flexible layered structure resulting in simultaneous intercalation and alloying process, the other approach uses a porous electrospun carbon fiber encapsulation for alloying compounds. The electrochemical properties as a function of Sn-content in a binary SnX (X: Sb) compound anode have been explicitly probed. This study provided invaluable information on alloying reaction mechanisms as well as identified the most optimum Sn-content for the long term stable battery operations. Usage of graphite as an anode in high energy density Li-ion cell has already been shown to be associated with severe safety issues. The thesis demonstrates a novel and very simple strategy to develop a stable non-carbonaceous anode for operation in the Li-ion (full) cell configuration. The thesis comprises of six chapters and a brief discussion of the content and highlights of the individual chapters are discussed below: Chapter 1 briefly reviews the different materials (mainly anodes) and storage mechanisms in the context of lithium-ion and sodium-ion rechargeable batteries. Energy storage via different mechanisms in metal-ion batteries has it’s own advantages and disadvantages. Thus, design of alternative novel materials is absolutely essential to nullify the detrimental factors associated with various storage methods leading to highly efficient and safe alkali metal-ion rechargeable battery systems. Development of materials for efficient alkali metal-ion batteries are very pertinent even today as the next generation high energy density rechargeable batteries based on metal-S/metal-O2 are still in the stages of infancy. They are far away from widespread commercialization and thus, do not pose any threat to the rechargeable alkali metal-ion batteries. This chapter discusses the importance of diffusion of ions inside the electrode materials, which essentially determines the rate capability of half/full cells. Chapter ends with discussion on galvanostatic intermittent titration technique (GITT) which has been used extensively for calculating the diffusion coefficients of the electrodes. Chapter 2 comprises of synthesis, characterization and investigation of electrochemical properties of novel Ti-based anode materials, namely Li-Ti-niobate and Na-Ti-niobate. These compounds are synthesized using a simple ion-exchange reaction from aqueous medium using KTiNbO5 (potassium titanium niobate) as the parent compound. Li-Ti-niobate and Na-Ti-niobate are tested in Li and Na-battery respectively as an anode material. The effects of Ti3+/Ti2+ redox couple in the electrochemical performances are also investigated in the case of Li-Ti-niobate by altering the working potential window of the battery. The electrochemical performances of Li-Ti-niobate are further improved by downsizing the particle size followed by carbon coating through hydrothermal carbonization method. Scheme 1: Layered structure of metal-titanium niobate. Electrochemical performance of Li-Ti-niobate in the voltage ranges (1-3) V and (0.2-2.75) V. The specific capacity of Li-Ti-niobate has been increased by downsizing the particles followed by carbon coating (cd-Li-Ti-niobate) in the voltage range (0.2-2.75) V. In Chapter 2 we investigated the electrochemical properties of Li-Ti-niobate as an anode material for Li-ion battery. In Chapter 3 we probed the ion diffusion inside the material, an important physical property that determines the possibility of battery operation at higher current densities. Layered Li-Ti-niobate shows pesudo-1-D Li+ ion diffusion, with ion transport taking place mainly along the crystallographic b-direction. Presence of line defects along crystallographic b-direction assists the diffusion to be pesudo-1-D in nature. Removal of line defects via sintering followed by studies on electrochemical properties suggests that presence of high density dislocation defects is crucial for superior rate performance of Li-Ti-niobate. Scheme 2: Preferential direction of ion diffusion in Li-Ti-niobate In the previous Chapters, the lithium ion intercalation behavior and its diffusion properties into titanium niobate layers have been investigated in detail. In Chapter 4, the same layered geometry has been explored to tackle the drastic volume expansion problem typically associated with anodes storing energy via the alloying method. Unique flexible non-carbonaceous layered host viz. M-Ti-niobate (Ti: Titanium; M: Al3+, Pb2+, Sb3+, Ba2+, Mg2+) has been designed which can synergistically store both lithium-ions and sodium-ions via simultaneous intercalation and alloying mechanisms. M-Ti-niobate is formed by ion-exchange of the K-ions, which are specifically located in the galleries between the layers formed by edge and corner sharing TiO6 and NbO6 octahedral units in the sol-gel synthesized potassium titanium niobate (KTiNbO5). The detrimental issues such as drastic volume changes (approximately 300-400%) typically associated with alloying mechanism of storage are completely tackled chemically viz. by the unique chemical composition and structure of the M-Ti-niobates. The free space between the adjustable Ti/Nb octahedral layers easily accommodates the drastic volume changes. Due to the presence of an optimum amount of multivalent alloying metal ions (50-75% of total K-ions) in the M-Ti-niobate, efficient alloying reaction takes place directly with the ions and completely eliminates any form of mechanical degradation of the electroactive particles. The M-Ti-niobate can be cycled over a wide voltage range (as low as 0.01 V) and displays remarkably stable Li+ and Na+ ion cyclability (> 2 Li+/Na+ per formula unit) for widely varying current densities over few hundreds to thousands of successive cycles. The simultaneous intercalation and alloying storage mechanisms demonstrated by the experiments is studied within the framework of density functional theory (DFT). DFT expectedly shows a very small variation in the volume of Al-titanium niobate following lithium alloying. Moreover, the theoretical investigations also conclusively endorse the occurrence of the alloying process of Li-ions with the Al-ions along with the intercalation process during discharge. The M-Ti-niobates studied here demonstrates a paradigm shift in chemical design of electrodes and will pave the way for development of multitude of improved electrodes for different battery chemistries Scheme 3: Scheme depicts the synergistic approach of charge storage in M-Ti-niobate anodes for alkali-ion rechargeable batteries. Colour changes in the layers indicate that the layers are electrochemically active. Chapter 5 mainly focuses on a fully Li-alloy based anode such as SnSb for prospective application in rechargeable Li-ion batteries. The Sn-content variation in SnSb nanoparticles confined inside electrically conducting carbon nanofiber is observed to significantly influence the electrochemical performance. It is a major challenge to minimize the detrimental effects arising as a result of drastic volume changes (≈ few hundred times) occurring during repeated alloying-dealloying of lithium with Group IV elements e.g. tin (Sn). An important design strategy is to have Sn as a component in a binary compound. SnSb, is an important example where the antimony (Sb) itself is redox active at a potential higher than that of Sn. The ability of Sb to alloy with Li reduces the Li uptake amount of Sn in SnSb compared to bare Sn. Thus, the volume changes of Sn in SnSb will expectedly be much lower compared to bare Sn leading to greater mechanical stability and cyclability. As revealed recently, complete reformation of SnSb (for molar ratio Sn:Sb= 1:1) during charging is not achieved due to loss of some fraction of Sn. Thus, molar concentration of Sn and Sb in SnSb is also absolutely important for the optimization of battery performance. We discuss here SnSb with varying compositions of Sn encapsulated inside an electrospun carbon-nanofiber (abbreviated as CF). The carbon-nanofiber matrix not only provides electron transport pathways for the redox process but also provides ample space to accommodate the drastic volume changes occurring during successive charge and discharge cycles. The systematic changes in the chemical composition of SnSb minimize the instabilities in the SnSb structure as well as replenish any loss in Sn during repeated cycling. The composition plays a very crucial role as magnitude of specific capacities and cyclability of SnSb is observed to depend on the variable percentage of Sn. SnSb-75-25-CF, which contains excess Sn, exhibits the highest specific capacity of 550 mAh g-1 after 100 cycles in a comparison with pure SnSb (1:1) anode material at current density (0.2 A/g) and shows excellent rate capability over widely varying current densities (0.2-5 A g-1). Scheme 4: Schematic depiction of lithiation and delithiation mechanism in SnSb. Bar diagram of specific capacity versus percentage of Sn present in SnSb-series of compounds. Percentage of Sn present is 0 %, 25%, 50%, 75% and 100% in Sb-CF, SnSb-25-75-CF, SnSb-50-50-CF, SnSb-75-25-CF and Sn-CF respectively. In Chapter 6 we discuss a binary mixture of two non-carbon coated electroactive compounds viz. anatase-titanium dioxide (TiO2) and vanadium pentoxide (V2O5) as a potential electrode for Li-based batteries. The binary mixture, whose components are synthesized using sol-gel methods and not carbon coated, can be reversibly cycled in the potential range (1.0-3.5) V against Li-metal. The physical mixture of the as-synthesized TiO2 and V2O5 (w/w = 1:1) provides a high specific capacity (≈ 190 mAh g-1 after 100 cycles at 100 mA g-1) and higher compared to the bare anatase-TiO2 and V2O5. Thus, this simple strategy enhances the operational potential of anatase-TiO2 by 0.5 V to 3.5 V against lithium and also nullifies greatly the complexities of carbon electronic wiring of electroactive particles. A Li-ion cell, comprising of the non-carbon coated binary mixture as anode and lithium manganese oxide (LiMn2O4) as the cathode, cycled in the potential range (0.2-3.5) V delivers a high specific capacity of nearly 80 mAh g-1 at 100 mA g-1 and is higher compared to the full cell capacities using the individual components as anodes. No signatures of SEI formation is observed from the cyclic voltammetry results. The presence of a second electroactive material may strongly suppress the SEI formation typically observed for Ti-oxide based materials when cycled to such a low potential (≈ 0.2 V). This may also account for the high percentage of reversibility and specific capacity of the full cell in this wide potential range. This simple approach enables the possibility of using Ti-oxide based anodes against the commercial intercalation cathodes without any compromise in the cell performance and also reduces the need for design of novel high voltage cathode materials. Scheme 5: Scheme shows a design strategy for improvement in specific capacity as a result of presence of an additional redox active species in the Li-ion configuration.

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.

Lithium Niobate has been the material of choice for OPO's used to generate mid infrared (2.5 to 4 μm) for atmospheric remote sensing by DIAL [1]. Such systems are capable of measuring a wide range of gaseous hydrocarbon species in the atmosphere. To a large extent the use of lithium niobate in theses OPO's has been a result of its widespread availability in large sizes and with good optical quality. Potassium niobate has always been a potential alternative which has the possible benefit of operating at longer wavelengths. Until recently, it has not been readily available in sizes or with the optical quality required for pulsed laser pumping. However, recent improvements in the growth and treatment of potassium niobate have made it a more realistic alternative.