B. Harihara Venkataraman

Optical diffraction of second-harmonic signals in the LiBO2-Nb2O5 glasses induced by self-organized LiNbO3 crystallites

The nanocrystallites ( ≈ 3 nm) of LiNbO3, evolved in the (100−x)LiBO2-xNb2O5 (5x20, in molar ratio) glass system exhibited intense second-harmonic signals in transmission mode when exposed to infrared (IR) light at λ = 1064 nm. The second-harmonic waves were found to undergo optical diffraction which was attributed to the presence of self-organized submicrometer-sized LiNbO3 crystallites that were grown within the glass matrix along the parallel damage fringes created by the IR laser radiation. Micro-Raman studies carried out on the laser-irradiated samples confirmed the self-organized crystallites to be LiNbO3.

Frequency Dependent Dielectric Characteristics of Undoped and Vanadium-Doped SrBi2Nb2O9 Ferroelectric Ceramics: A Comparative Study

The dielectric properties of undoped and vanadium (10 mol%) doped SrBi 2 Nb 2 O 9 ferroelectric ceramics were studied in the 100 Hz to 1 MHz frequency range at various temperatures (300–823 K). The dielectric constants of vanadium doped ceramics were higher than those of undoped ceramics. A strong low frequency dielectric dispersion (LFDD) was encountered in these ceramics in the 573–823 K temperature range. The dispersion was stronger at low frequencies and higher temperatures for vanadium - doped ceramics. The dielectric constants measured in the wide frequency and temperature ranges for both the samples were found to fit well to the Jonschers dielectric dispersion relations: ϵ r ′ = ϵ∞+ sin (n (T) π /2) ω n(T) − 1 a(T)/ϵ o and ϵ r ″ = σ/ϵ o ω + cos (n (T) π /2) ω n(T) − 1 a(T)/ϵ o . The lattice dielectric constant (ϵ∞) shows a peak at T c . The coefficient A(T)(= a(T)S/L) and the exponent n (T) of the Jonschers expression were determined. The exponent n (T) was found to be minimum at the Curie temperature, T c . The value of n for the vanadium—doped samples was less than that of the undoped one. The parameter A(T), which indicates the polarizing power, showed a prominent peak in the vicinity of the Curie temperature for both the samples. However, the value of A for the vanadium—doped samples was higher than that of undoped SBN ceramics.

Dielectric and electrical conductivity characteristics of undoped and samarium doped ferroelectric SrBi2Ta2O9 ceramics derived from molten salt synthesis route

ABSTRACT Undoped and samarium doped SrBi2Ta2O9 ferroelectric ceramics have been fabricated by the molten salt synthesis route. The dielectric and electrical conductivity measurements were carried out in the 100 Hz – 1 MHz frequency range at various temperatures. A decrease in dielectric constant maximum (ϵm) and a downward shift in the Curie transition temperature (Tc) have been observed with the increase in samarium concentration.The frequency dependence real and imaginary parts of dielectric constant of these ceramics exhibited low frequency dielectric dispersion. Interestingly, temperature and frequency dependence dielectric constant plots indicated that the formation of oxygen ion vacancies have inhibited by samarium doping in SBT lattice. The activation energy values obtained from the Arrhenius plot have confirmed the existence of motion of oxygen ion vacancies in these ceramics.

Structural and Dielectric Properties of Strontium Bismuth Samarium Tantalate Layered Perovskites

The polycrystalline Sr(Bi0.9Sm0.1)2Ta2O9 (SBSmT) ceramics were fabricated via the promising low temperature molten salt synthesis route using KCl as flux material. The X-ray powder diffraction patterns of these ceramics confirmed the existence of monophasic perovskite crystal structure. The scanning electron microscopic studies revealed the presence of plate shaped morphological features of the SBSmT ceramics. Interestingly, the dielectric constant of the SBSmT ceramics in the frequency range of 20 Hz - 1MHz could be tuned as a function of sintering duration. It is observed that the SBSmT ceramics sintered at 1050°C for 10h exhibited higher dielectric constant (ϵr = 76) at 100 kHz than those of ceramics sintered at other durations. The magnitude of the electrical conductivity of the order of 10−7 - 10−9 S/cm at 300 K indicates that the conductivity mechanism might be attributed to the migration of oxygen ion vacancies in these ceramics.

Structural, Dielectric, Pyroelectric and Ferroelectric Properties of Glass Nano Composite: Lithium Borate-Strontium Bismuth Vanadium Niobate

Transparent glasses in the system (100 − x) (Li2O − 2B2O3) − x (SrO − Bi2O3 − 0.7 Nb2O5 − 0.3 V2O5) (10 ≤ x ≤ 60, in molar ratio) were fabricated via the melt quenching technique. The as-quenched samples were X-ray amorphous. Differential thermal analysis (DTA) confirmed the glassy nature of the as-quenched samples. Strontium bismuth vanadium niobate nanorods were grown by controlled heat-treatment of the as-quenched glasses at 783 K for 6 h. The formation of nanorod layered perovskite SrBi2(Nb0.7V0.3)2O9-δ (SBVN) phase via an intermediate fluorite phase was confirmed by both X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). The dielectric constants of both the as-quenched and heat-treated samples (783 K/6 h) increased while the dielectric loss (D) decreased with increasing x (SBVN content). Interestingly, the dielectric constant of the glass nanocrystal composite (heat-treated at 783 K/6 h) exhibited an anomaly in the vicinity of the crystallization temperature of the host glass (Li2B4O7) reaching a value as high as ≈106 at 800 K. These glass nanocrystal composites were pyroelectric and ferroelectric at 300 K. Communicated by George W. Taylor

The Microstructural, Dielectric, Pyroelectric and Ferroelectric Properties of SrBi2(Nb1-xVx)2O9(0 ≤ x ≤ 0.3) Ceramics

Layered SrBi2(Nb1−x V x )2O9 (SBVN) ceramics with x ranging from 0 to 0.3 (30 mol%) were fabricated via the conventional sintering technique. A remarkable transformation in the microstructure of SBN ceramic was encountered as the V2O5 content increased from 3–30 mol%. The average grain size of the SBN ceramic containing V2O5 was found to increase with increase in V2O5 content. The dielectric constant (ϵ r ) as well as the dielectric loss (D) increased with increase in grain size (6 μm–17 μm). The ferroelectric to paraelectric transition temperature (T c ) shifted to higher temperature with increasing grain size. The pyroelectric coefficient was positive at 300 K and increased with increasing grain size. Interestingly, the SrBi2(Nb0.7V0.3)2O9 (x = 0.3) ceramics with a grain size of 17 μm exhibited higher remnant polarization (P r ) and lower coercive field (E c ) than those with grains of 7 μm. The Curie-Weiss constant that was obtained for these ceramics was in line with that of displacive type ferroelectrics.

Dielectric relaxor and conductivity characteristics of undoped and samarium doped barium bismuth niobate ferroelectric ceramics

ABSTRACT The polycrystalline BaBi2Nb2O9 and Ba(Bi0.9Sm0.1)2Nb2O9 ceramics have been fabricated via the molten salt synthesis route. The temperature dependence of dielectric and electrical conductivity properties of BBN and BBSmN ceramics investigated at various frequencies have revealed the characteristic features of relaxor behaviour. The incorporation of Sm3+ for Bi3+ has induced a downward shift in the dielectric maximum temperature (165°C–120°C) with the decrease in dielectric constant maximum (372 – 212) at 100 kHz. The estimated degree of diffuseness (γ) was found to be 2.17 for BBN and 1.93 for BBSmN ceramic samples. The activation energy obtained from the Arrhenius plot revealed the existence of motion of oxygen ion vacancy in these ceramics.

An Integrated Use of Biopolymer-Ceramic Composites Towards Capacitor and Environmental Application

Biopolymer composite films comprising strontium titanate crystallites in [(100 - x) Cellulose - xSrTiO3] (0 ≤ x ≤ 90, in wt %) system were fabricated via solution casting technique. The X-ray diffraction (XRD) and scanning electron microscopic (SEM) studies were carried out on these composite films for structural and microstructural analyses. The dielectric constant of these composites increased with the concentration of strontium titanate crystallites dispersed in the cellulose matrix. Different dielectric mixture formulae were employed to rationalize the dielectric properties of the biopolymer composite systems. The composite films also showed promising application towards the removal of toxic chromium(VI).