In recent years bismuth-based, layer-structured perovskites such as SrBi2Nb2O9 (SBN) and SrBi2Ta2O9 (SBT) have been investigated extensively, because of their potential use in ferroelectric random access memories (FeRAMs). In comparison with non-layered perovskite ferroelectrics such as Pb(Zr,Ti)O3 (PZT), these offer several advantages such as fatigue free, lead free, low operating voltages and most importantly their ferroelectric properties are independent of film thickness in the 90 to 500 nm range. For FeRAM device applications, large remnant polarization (Pr), low coercive field (Ec) accompanied by high Curie temperature (Tc) are required for better performance and reliable operation. Much effort has been made to improve the ferroelectric properties of SBN and SBT ceramics by doping on A or B sites. It was known in the literature that partial substitution of Sr2+ by Bi3+ ions in SBN and SBT would increase the Curie temperature and improve the dielectric properties. The focus of the investigations that were taken up was to improve the electrical, dielectric and ferroelectric characteristics of SrBi2Nb2O9 ceramics. It was reported that the ferroelectric and nonlinear optical properties of LiNbO3 and LiTaO3 could be improved when vanadium, the lightest element in group V of the periodic table is substituted for Nb or Ta along with Li and three oxygens. It is with this background the investigations have been taken up to see whether one can extend the same argument to the Aurivillius family of oxides. Therefore, the central theme of the present investigations aimed at substituting Nb5+ by a smaller cation V5+ in SBN and study its influence on the formation temperature, sinterability, structural and microstructural characteristics apart from its physical properties. Recently the optical properties of this material have been recognized to be important from the optical device point of view. Unfortunately single crystal growth of vanadium doped SBN was hampered because of the bismuth and vanadium loss (high volatility) observed in the process of growth. One of the routes that attracted our attention has been the glass-ceramic. It would be interesting to visualize the behavior of crystallites of nano/micrometer size embedded in a glass matrix as these crystals were known to give rise to exotic properties. One of the crucial steps in the process of fabrication of a glass nanocrystalcomposite system in which crystalline phases have symmetries that would eventually give rise to basic non - centrosymmetric properties such as piezoelectric, pyroelectric and Pockels effects, has been to choose a compatible matrix material associated with easy glass forming capability and the ability to evenly disperse dipolar defects within itself. Recent investigations into strontium borate SrB4O7 (SBO), lithium borate Li2B4O7 (LBO) glasses indicated that LBO by virtue of its favorable structure, thermal and optical properties would form a suitable host glass matrix for dispersing layer structured ferroelectric oxides belonging to the Aurivillius family of oxides. Since lithium borate has wide transmission window, it was worth making an attempt to fabricate optical composite of Li2B4O7 (LBO) and vanadium doped SrBi2Nb2O9 (SBVN) and to study its structural, dielectric, pyroelectric, ferroelectric and optical properties. Therefore the present thesis reports detailed investigations into the effect of vanadium doping on the structural and various physical properties of an n = 2 member of the Aurivillius family of oxides in the polycrystalline form and novel glass composites comprising nano/microcrystallites of this phase. Chapter 1 comprises a brief introduction to the dielectric, pyroelectric, ferroelectric and nonlinear optical properties of materials. In addition to the principles and phenomena, the material aspects of these important branches of physics are discussed. It also forms a preamble to the glasses, criteria for glass formation, glass – ceramics and subsequently ferroelectric and nonlinear optical effects that were observed in glasses and glass - ceramics. Chapter 2 describes the material fabrication techniques adopted to prepare polycrystalline and grain – oriented ceramics, glasses and glass nanocrystalcomposites. The details of various structural, dielectric, pyroelectric, ferroelectric and optical measurement techniques employed to characterize these materials are also included. Chapter 3 discloses the fabrication of strontium bismuth niobate ceramics and their characterization for dielectric and impedance properties. The dielectric properties of strontium bismuth niobate ceramics have been modeled based on Jonscher’s Universal formalism. The coefficients of the Jonscher’s expression, exponent n(T) undergoes a minimum and A(T) exhibits a peak at the Curie temperature, Tc (723K). A strong low frequency dielectric dispersion (LFDD) associated with an impedance relaxation has been found to exist in these ceramics in the temperature range 573 - 823K. The Z′′ of the AC complex impedance showed two distinct slopes in the frequency range 100Hz-1MHz suggesting the existence of two dispersion mechanisms. The exponents m and n were obtained from the curve fitting. The exponent n was found to exhibit a minimum at the Curie temperature, Tc (723K) whereas the m was temperature independent. Chapter 4 deals with the fabrication of vanadium doped SrBi2Nb2O9 ceramics and their characterization for microstructural, dielectric, pyroelectric and ferroelectric properties. The average grain size of the SrBi2Nb2O9 (SBN) ceramic containing V2O5 was found to increase with increase in V2O5 content. The dielectric constant (εr) as well as the dielectric loss (D) increased with increase in grain size (6µm-17µm). The pyroelectric coefficient was found to be positive at 300K and showed an increasing trend with increasing grain size. Interestingly, the SrBi2(Nb0.7V0.3)2O9-δ ceramics consisting of 17µm sized grains showed higher remnant polarization (Pr) and lower coercive field (Ec) than those with grains of 7µm. Chapter 5 deals with the dielectric properties which were studied in detail in the 100Hz to 1MHz frequency range at various temperatures (300 – 823 K) for undoped and vanadium (10 mol%) doped SrBi2Nb2O9 (SBVN10) ferroelectric ceramics. A strong low frequency dielectric dispersion was encountered in these ceramics in the 573 – 823 K temperature range. The dielectric constants measured in the wide frequency and temperature ranges for both the samples were found to fit well to the Jonscher’s dielectric dispersion relations. The dielectric behavior of SBN and SBVN10 ceramics was rationalized using the impedance and modulus data. The electrical conductivity studies of layered SrBi2(Nb1-xVx)2O9-δ ceramics with x lying in the range 0 to 0.3 (30 mol%) were centered in the 573 – 823K temperature range as the Curie temperature lies in this range. The concentration of mobile charge carriers (n), the diffusion constant (D0) and the mean free path (a) were calculated using Rice and Roth formalism. The conductivity parameters such as ion hopping rate (ωp) and the charge carrier concentration (K′) term have been calculated using Almond and West formalism. The afore mentioned microscopic parameters were found to be V2O5 content dependent in SrBi2(Nb1-xVx)2O9-δceramics. Chapter 6 describes the fabrication of partially grain – oriented SrBi2(Nb1-xVx)2O9-δ (0 ≤x≤3.0 in molar ratio) ceramics and characterization for their structural, microstructural, dielectric, pyroelectric and ferroelectric properties. The grain – orientation factor and the microstructural features were studied by XRD and scanning electron microscopy as a fuction of sintering temperature and V2O5 content. The dielectric constant measured along the direction parallel and perpendicular to the pressing axis has shown a significant anisotropy. The pyroelectric and ferroelectric properties were superior in the direction perpendicular to the pressing axis (polar) to that in the parallel direction. The fabrication and characterization details of (100 – x) (Li2B4O7) – x (SrO - Bi2O3 - 0.7 Nb2O5 – 0.3 V2O5) (10 ≤ x ≤ 60, in molar ratio) glasses and glass nanocrystal composites are dealt within Chapter 7. The nanocrystallization of strontium bismuth niobate doped with vanadium (SrBi2(Nb0.7V0.3)2O9-δ(SBVN)) has been demonstrated in Li2B4O7 glasses. The glassy nature of the as – quenched samples was established by differential thermal analyses (DTA). The amorphous nature of the as – quenched glasses and crystallinity of glass nanocrystal composites were confirmed by X – ray powder diffraction studies. High resolution transmission electron microscopy (HRTEM) of the glass nanocrystal composites (heat – treated at 783K/6h) confirm the presence of nano rods of SBVN embedded in Li2B4O7 glass matrix. Chapter 8 presents the physical properties of the glasses and glass nanocrystal composites. Dielectric constant of both the as – quenched and glass nanocrystal composites was found to increase with increase in the composition, whereas the loss was observed to decrease with increasing SBVN composition. Different dielectric mixture formulae were employed to analyze the dielectric properties of the glass nanocrystal composite. The electrical behaviour of the glasses and glass nanocrystal composites was rationalized using impedance spectroscopy. The observed pyroelectric response and ferroelectric hysteresis of these composites confirmed the polar nature. Various optical parameters such as optical band gap (Eopt), Urbach energy (∆E), refractive index (n), optical dielectric constant (ε′∞) and ratio of carrier concentration to the effective mass (N/m*) were determined. The effects of composition of the glasses and glass nanocrystal composites on these parameters were studied. Transparent glasses embedded with nanocrystallites of SBVN exhibited intense second harmonic signals in transmission mode when exposed to IR laser light at λ = 1064 nm. The thesis ends with a summary of the important findings and conclusions.

Borate glasses and glass-nano/microcrystal composite fabrication and investigations into their physical properties, have been interesting from their multifunctionalities view point. Certain borate structural units possess high hyperpolarizabilities and give rise to high nonlinear optical effects. High refractive index materials are important for photonic applications. Heavy metal oxide (Bi2O3) containing compounds have high refractive indices. Glasses embedded with wide band-gap semiconducting oxide crystals such as TiO2 received much attention due to their easy processing, stability and promising physical properties. Though TiO2 is used as nucleating agent to fabricate glass-ceramics of various phases, crystallization of TiO2 in glass matrices is difficult and the data are scarce in the literature. Therefore it was worth attempting to find glass compositions in which one can obtain TiO2 crystallization in large volume fractions. Towards this TiO2 crystallization was accomplished in BaO-TiO2-B2O3 glass matrix over wide composition ranges by tuning the concentration of BaO-TiO2 content in B2O3 network. The physical properties of these glasses of various compositions and glass-nanocrystal composites of TiO2 phase (anatase) were investigated. Interestingly BaO-TiO2-B2O3 glasses found to be hydrophobic in nature. The results obtained in the present research work are classified into five chapters apart from the Introduction, Materials and Methods chapters. Chapter 1 constitutes preface to oxide glasses, principles of glass formation and structural criteria followed by crystallization kinetics. In addition, principles of dielectric, optical and mechanical phenomena in glasses are discussed, since the present thesis focuses on the aforesaid physical properties. This chapter concludes with scope of the present thesis. Chapter 2 includes the detailed description concerning the fabrication techniques of materials under study and various characterization methods that have been employed at various stages of the present research work. The principles and experimental tools adopted for the structural and microstructural studies of materials were illustrated. Measurement techniques and experimental setup used to study physical parameters such as dielectric, optical, mechanical etc. were elaborated. Chapter 3 comprises structural, dielectric, electrical transport characteristics and optical studies of mixed alkali borate glasses in the 0.5Li2O-0.5M2O-2B2O3 (M=Li, Na and K) system. Transparent glasses in the Li2O-2B2O3 (LBO), 0.5Li2O-0.5Na2O-2B2O3 (LNBO) and 0.5Li2O-0.5K2O-2B2O3 (LKBO) were fabricated via the conventional melt quenching technique. Amorphous and glassy nature of the samples was confirmed via the X-ray powder diffraction and the differential scanning calorimetry, respectively. LKBO glass was found to have high thermal stability than that of LBO and LNBO. The frequency and temperature dependent characteristics of the dielectric relaxation and the electrical conductivity were investigated in the 100 Hz - 10 MHz frequency range. The relaxation and conductivity were rationalized using impedance and modulus formalism. Imaginary part of the electric modulus spectra was modelled using an approximate solution of Kohlrausch-Williams-Watts relation. The stretching exponent, β, was found to be temperature independent for LNBO glasses. Activation energies for conduction and relaxation process were calculated using the Arrhenius relation. The activation energy was found to be higher (1.25eV) for LKBO glasses than that of the other glass systems under study. This is attributed to the mixed cation effect. It has wide optical transmission window and optical band gap. Urbach energies were calculated for all these glasses. LBO, LNBO and LKBO glass compositions were found to crystallize in Li2B4O7, LiNaB4O7 and LiKB4O7 phases respectively upon heat treatment at appropriate temperatures. Transparent glass-micro crystal composites of LiKB4O7 were fabricated from LKBO glasses and found to be SHG active. BaO-TiO2-B2O3 Chapter 4 delineates the evolution of nanocrystalline TiO2 phase (Anatase) in BaO-TiO2-B2O3 (BTBO) glasses. Transparent colourless glasses in the ternary system were fabricated via conventional melt-quenching technique. The glasses with certain molar concentrations of BaO and TiO2 upon heat treatment at appropriate temperatures yielded nanocrystalline phase of TiO2 associated with the crystallite size in the 5-15 nm range. Nanocrystallized glasses exhibited high refractive index (no=2.15) at λ=543nm. These glasses were found to be hydrophobic in nature associated with the contact angle of 90o. These high index glass nanocrystal composites would be of potential interest for optical device applications. Crystallization kinetics of anatase phase in BTBO glasses were studied using non-isothermal Differential Scanning Calorimetry (DSC) at three different heating rates (10, 20 & 30 K/min). Scanning Electron Microscopy (SEM) carried out on heat treated (at 920 K) glasses confirmed bulk nucleation and three-dimensional growth. Johnson-Mehl-Avrami model could not be applied for this system suggesting considerable overlap of the nucleation and growth involving complex transformation process. However, modified Kissinger and Ozawa models were used to calculate the effective activation energy associated with anatase crystallization. The kinetic exponent n was found to be temperature dependent indicating the change in the crystallization mechanism. This is attributed to the high entropy fusion of anatase phase, fast crystallization rate and nano dimension of the anatase phase. Chapter 5 illustrates structural changes that occur in the x(BaO-TiO2)-B2O3 (x=0.25, 0.5, 0.75 &1 mol.) system on increasing the x apart from the details concerning some physical property correlations. Thermal stability and glass forming ability as determined by Differential Thermal Analysis (DTA) were found to increase with increasing BaO-TiO2 (BT) content. However, there was no noticeable change in the glass transition temperature (Tg). This was attributed to the active participation of TiO2 in the network formation especially at higher BT contents via the conversion of the TiO6 structural units into TiO4 units which increased the connectivity and resulted in an increase in crystallization temperature. Dielectric and optical properties at room temperature were studied for all the glasses under investigation. Interestingly, these glasses were found to be hydrophobic. The results obtained were correlated with different structural units present in the glass and their connectivity. These glasses exhibited low loss (tan δ≈0.002), frequency (10 kHz- 10 MHz) and temperature independent (or very weak temperature response) flat-dielectric response. Crossover temperature was encountered between flat response and Jonscher’s universal response. The cross-over temperature and cross-over energy barrier from flat dielectric response to Jonscher’s response was deduced for all the glasses in the present investigation. Electric modulus formalism was invoked to rationalize the relaxation phenomena. The observed dielectric response and conduction process in these glasses were attributed to the local vibration and switching of non-bridging oxygen ions in their potential cage and hopping over distributed energy barriers above the crossover temperature. Chapter 6 depicts the dielectric and mechanical properties of glasses embedded with TiO2 nanocrystals. BaO-TiO2-B2O3 glasses on subjecting to appropriate heat treatment temperature yielded TiO2 nano crystalline anatase phase. NMR studies carried out on the as-quenched glasses facilitated the estimation of fraction of tetrahedral and trigonal borate units. Poisson’s ratio and Young’s modulus were evaluated through theoretical expressions proposed by Makishima and Mackenzie. Nano-indentation and micro-indentation studies were carried out on the as-quenched glasses and glass-nanocrystal composites to examine mechanical characteristics. Estimated and indentation Young’s modulus of glasses were found to be in reasonable agreement. Hardness and Young’s modulus increased with increasing fraction of nano crystallites whereas fracture toughness was found to depend strongly on surface conditions. The results were corroborated by the structural units and particulates present in these glasses. Dielectric constant increased with increasing volume fraction of the nanocrystals which was rationalized via mixture rule. Chapter 7 describes the dielectric properties, electrical conduction and electric relaxation phenomena in 2Bi2O3-B2O3 (BBO) glasses followed by thier linear and nonlinear optical characteristics. Glasses in BBO system were obtained via melt-quenching technique. X-ray diffraction and differential scanning calorimetry were used to study the structural characteristics. Dielectric studies carried out on these glasses revealed near constant loss (NCL) response in the 1 kHz to 1 MHz frequency range at moderately high temperatures (300-450 K) accompanied by relatively low loss (tan δ=0.006, at 1 kHz & 300 K) and high dielectric constant (ε' =37, at 1 kHz & 300 K). The variation in AC conductivity with temperature at different frequencies showed a cross over from NCL response characterized by local ion vibration within the potential well to universal Jonscher’s power law dependence triggered by ion hopping between potential wells or cages. Thermal activation energy for single potential well was found to be 0.48±0.05 eV from cross over points. Ionic conduction and relaxation processes were rationalized by modulus formalism. The promising dielectric properties (relatively high ε' and low tan δ) of the BBO glasses were attributed to high density (93 % of its crystalline counterpart), high polarizability and low mobility associated with heavy metal cations, Bi3+. Optical band gap obtained for BBO glasses was found to be 2.6 eV. The refractive index measured for these glasses was 2.25±0.05 at λ=543 nm. Nonlinear refraction and absorption studies were carried out on BBO glasses using z-scan technique at λ=532 nm of 10 ns pulse width. The nonlinear refractive index obtained was n2=12.1x10-14 cm2/W and two-photon absorption coefficient was β=15.2 cm/GW. The n2 and β values of the BBO glasses were higher than that reported for high index bismuth based oxide glass systems in the literature. These were attributed to the high density, high linear refractive index, low band gap and two-photon absorption associated with these glasses. The electronic origin of large nonlinearities was discussed based on bond-orbital theory. Thesis ends with summary and conclusions followed by prospective views, though each chapter comprises conclusions associated with complete list of references. Patent, publications and conference proceedings that are listed below are largely based on the studies conducted as a part of the research work reported in the present thesis.

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.

Ferroelectric materials are very promising for a variety of applications such as high-permittivity capacitors, ferroelectric memories, pyroelctric sensors, piezoelectric and electrostrictive transducers and electro-optic devices, etc. In the area of ferroelectric ceramics, lead-based compounds, which include lead zirconatetitanate (PZT) solid solutions, occupy an important place because of their superior physical properties. However, due to the toxicity of lead, there is an increasing concern over recycling and disposing of the devices made out of these compounds, which has compelled the researchers around the globe to search for lead-free compounds with promising piezo and ferroelectric properties. Ferroelectric materials that belong to Aurivillius family of oxides have become increasingly important from the perspective of industrial applications because of their high Curie-temperatures, high resistivity, superior polarization fatigue resistanceand stable piezoelectric properties at high temperatures. These bismuth layer-structured ferroelectrics (BLSF) comprise an intergrowth of [Bi2O2]2+ layers and [An+1Bn O3n+1]2- pseudo-perovskite units, where ‘n’ represents the number of perovskite-like layers stacked along the c-axis. ‘A’ stands for a mono-, di- or trivalent ions or a combination of them, ‘B’ represents a small ion with high valencysuch as Ti4+, Nb5+, Ta5+or a combination of them.Ferroelectricity in the orthorhombic phase of these compounds was generally attributed to the cationic displacement along the polar a-axis and the tilting of octahedra around the a- and c-axes. Sr2Bi4Ti5O18(SBT) is ann = 5 member of the Aurivillius family and possess promising ferroelectric and piezoelectric properties that could be exploited for a wide range of applications, including ferroelectric random access memories (FeRAM), piezoelectric actuators, transducers and transformers. Reports in the literaturereveal that the ferroelectricand piezoelectric properties of these oxides can be tuned depending on synthesis routes vis-a-vis micro-structural aspects (texture, grain size) and site specific dopant substitutions.In the present study, textured SBT ceramics were fabricated using pre-reacted precursors and their anisotropic dielectric, piezoelectric and ferroelectric properties were demonstrated. Grain size tunability with regard to their physical properties was accomplished in the ceramics, fabricated using fine powders obtained from citrate assisted sol-gel synthesis. The grain size dependent second harmonic generation activity of SBT ceramics was investigated. Enhancement in the piezoelectric and ferroelectric properties of SBT ceramics was achieved by substituting A site ions (Sr2+) with a combination of Na+ and Bi3+. From the perspective of non-linear optical device applications, physical properties associated with the SBT crystallized in a transparent lithium borate glass matrix were studied. The results obtained in the present investigations are organized as follows, Chapter 1 gives a brief exposure to the field of ferroelectrics. The emphasis has been on the ferroelectric oxides belonging to the Aurivillius family. Structural aspects and the underlying phenomena associated with ferroelectricity in these compounds are discussed. A brief introduction to the glasses, thermodynamic aspects of glass formation and fabrication of glass- ceramics are included. Basic principles involved in the non-linear optical activities are highlighted. Chapter 2 describes the various experimental techniques that were employed to synthesize and characterize the materials under investigation. The experimental details pertaining to the measurement of various physical properties are included. Chapter 3 deals with the fabrication of Sr2Bi4Ti5O18 ceramics using the pre-reacted Bi4Ti3O12 and SrTiO3 powders viasolid-state reaction route. These in stoichiometric ratio were uniaxially pressed and sintered at 1130oC for 3 h resulting in textured Sr2Bi4Ti5O18 ceramics. The obtained dense ceramics exhibited crystallographic anisotropy with prominent c-axis oriented grains (Lotgering factor of 0.62) parallel to the uniaxially pressed direction. The resultant anisotropy in the ceramics was attributed to the reactive template-like behavior of Bi4Ti3O12 that was used as a precursor to fabricate Sr2Bi4Ti5O18 ceramics. Dielectric, ferro and piezoelectric properties measured on the ceramics in the direction perpendicular to the uniaxially pressed axis were found to be superior to that measured in the parallel direction. Chapter 4 reports the details pertaining to the synthesis of strontium bismuth titanate (Sr2Bi4Ti5O18) powders comprising crystallites of average sizes in the range of 94–1400 nm via citrate-assisted sol-gel route. X-ray powder diffraction, Transmission Electron Microscopy (TEM) and Raman spectroscopy were employed for the structural studies. A crystallite size-dependent variation in the lattice parameters and the shift in the Raman vibration modes were observed. Second harmonic signal (532 nm) intensity of the Sr2Bi4Ti5O18 powders increased with the increase in the average crystallite size and the maximum intensity obtained in the reflection mode was 1.4 times as high as that of the powdered KH2PO4. Piezo force microscopic analyses carried out on an isolated crystallite of size 74 nm, established its single domain nature with the coercive field as high as 347 kV/cm. There was a systematic increase in the d33 value with an increase in the size of the crystallite and a high piezoelectric coefficient of ~27 pm/V was obtained from an isolated crystallite of size 480 nm. Chapter 5 illustrates the details concerning the fabrication of Sr2Bi4Ti5O18(SBT) ceramics with different grain sizes (93 nm–1.42 μm) using nano-crystalline powders synthesized via citrate assisted sol-gel method. The grain growth in these powder compacts was found to be controlled via the grain boundary curvature mechanism, associated with anactivation energy of 181.9 kJ/mol. Interestingly with a decrease in grain size there was an increase in the structural distortion which resulted in a shift of Curie-temperature (phase transition) towards higher temperatures than that of conventional bulk ceramics. Extended Landau phenomenological theory for the ferroelectric particles was invoked to explain experimentally observed size dependent phase transition temperature and the critical size for SBT is predicted to be 11.3 nm. Grain size dependent dielectric, ferroelectric and piezoelectric properties of the SBT ceramics were studied and the samples comprising average grain size of 645 nm exhibited superior physical properties that include remnant polarization (2Pr) = 16.4 μC cm-2, coercive field (Ec) = 38 kV cm-1, piezoelectric coefficient (d33) = 22 pC N-1 and planar electromechanical coupling coefficient (kp) = 14.8 %. In Chapter 6, the studies pertaining to the fabrication of Sr(2-x)(Na0.5Bi0.5)xBi4Ti5O18 (SNBT) ceramics for various x values (0, 0.1, 0.25, 0.3, 0.4 and 0.5), using fine powders synthesized via sol-gel route are dealt with. X-ray powder diffraction, transmission electron microscopy and Raman spectroscopic studies were carried out to confirm composition dependent structural changes taking place in the SNBT ceramics. Scanning electron microscopic studies carried out on ceramics revealed that dopants played an important role in inhibiting the grain growth. Dielectric constants of the ceramics were found to decrease with an increase in ‘x’. The increase in Curie temperature with increase in ‘x’ is attributed to the decrease in the tolerance factor. Particularly,x = 0.3 composition of the SNBT ceramics exhibited better piezo and ferroelectric properties with a higher Curie-temperature (569 K). The piezoelectric coefficient (d33) and the planar electromechanical coupling coefficient (kp) of SNBT(x = 0.3) were enhanced by 25% and 42% respectively as compared to that of the undoped ceramics. Chapter 7 deals with the glasses in the system (100 –x) {Li2O + 2B2O3} ─x {2SrO + 2Bi2O3 +5TiO2} (where, x = 10, 25 and 35) fabricated via conventional melt-quenching technique. The amorphous and glassy characteristics of the samples were confirmed respectively using X-ray diffraction (XRD) and differential scanning calorimetric (DSC) methods. All the compositions under investigation exhibited two distinct crystallization peaks (exothermic peaks in the DSC traces): the first peak at ~ 545 °C and the second at ~610 °C that were found to be associated with the crystallization of the phases (as confirmed from the XRD studies) Sr2Bi4Ti5O18 (SBT)and Li2B4O7 (LBO) respectively. Non-isothermal crystallization kinetics (using modified Ozawa-type plots) for SBT crystallization in the LBO glass matrix for the compositions x = 10 and 35, indicated three dimensional growth of the crystallites from pre-existing nuclei present in the as-quenched samples and their effective activation energies for crystallization were found to be around 686 ± 85 kJ/mol and 365 ± 53 kJ/mol, respectively. The optical band gap of the as-quenched glasses for the composition x = 35 was 2.52 eV, is less than that of the composition x = 10 (2.91 eV). The Urbach energies for the as-quenched glasses of compositions x = 10, 25 and 35 were found to be 118 ± 2 meV, 119 ± 2 meV and 192 ± 1 meV respectively.The glasses associated with the composition x = 35, on controlled heat-treatment at 515 °C for various durations (1―20 h), yielded glass-ceramics comprising SBT nano-crystals (18―28 nm) embedded in the LBO glass matrix. Compressive strain in the nano-crystallites of SBT, analyzed using Williamson-Hall method was found to decrease with an increase in the crystallite size. The second harmonic generation signal (532 nm) intensity emanating from glass-nanocrystal composites comprising 22.1 nm SBT crystallites was nearly 0.3 times that of a KDP single crystal. Although each chapter is provided with conclusions and a list of references, thesis ends with a separate summary and conclusions.