N. Syam Prasad

Evolution and characterization of fluorite-like nano-SrBi2Nb2O9 phase in the SrO–Bi2O3–Nb2O5–Li2B4O7 glass system

Abstract Transparent glasses of various compositions in the system (100− x )Li 2 B 4 O 7 − x (SrO–Bi 2 O 3 –Nb 2 O 5 ) (where x =10, 20, 30, 40, 50 and 60, in molar ratio) were fabricated via splat quenching technique. The glassy nature of the as-quenched samples was established by differential thermal analyses. X-ray powder diffraction (XRD) and transmission electron microscopic studies confirmed the amorphous nature of the as-quenched and crystallinity in the heat-treated samples. Fluorite phase formation prior to the perovskite SrBi 2 Nb 2 O 9 phase was analyzed by both the XRD and high-resolution transmission electron microscopy. Dielectric and the optical properties (transmission, optical band gap and Urbach energy) of these samples have been found to be compositional dependent. Refractive index was measured and compared with the values predicted by Wemple–Didomemenico and Gladstone–Dale relations. The glass nanocomposites comprising nanometer-sized crystallites of fluorite phase were found to be nonlinear optic active.

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.

Glass nanocomposite of strontium bismuth niobate and lithium borate : structural and dielectric investigations

Glass nanocomposites (GNC) in the system (100 - x)Li2B4O7 - xSrBi(2)Nb(2)O(9) (0 less than or equal to x less than or equal to 30) were prepared by splat quenching technique. The as-quenched samples of all the compositions under study have been confirmed to be amorphous by X-ray powder diffraction (XRD) studies. Differential thermal analyses (DTA) suggest the glassy nature of the as-quenched samples. High-resolution transmission electron microscopic (HRTEM) studies carried out on heat-treated samples reveal the presence of platy crystallites of SrBi2Nb2O9(SBN) dispersed in the glassy matrix of Li2B4O7 (LBO). The dielectric constant (epsilon (r)) and the dielectric loss (D) decrease with increase in frequency (100 Hz-10 MHz) at 300 K. The influence of the composition and the microstructure on the dielectric properties of the LBO-SBN nanocomposite has been established. The optical transmission characteristics of these GNC could be varied as a function of its composition.

Dielectric anomaly in strontium borate-bismuth vanadate glass nanocomposite

Transparent glass nanocomposites in the pseudo binary system (100 - x) SrB4O7 (SBO)-x Bi2VO5.5 (BiV) (0 less than or equal to n less than or equal to 70) were prepared by the splat quenching technique. The nano-crystallization of bismuth vanadate (BiV) in 50 SBO-50 BiV (in mol%) glass composite has been demonstrated. These were characterized for their structural, thermal and dielectric properties. As-quenched composites under study have been confirmed to be amorphous by X-ray powder diffraction (XRD) studies. The glass transition temperature (T-g) and crystallization temperatures (T-er) were determined using differential thermal analyses (DTA), High resolution transmission electron microscopic (HRTEM) studies carried out on heat-treated samples reveal the presence of spherical nanosize crystallites of Bi2VO5.5 (BiV) dispersed in the glassy matrix of SrB4O7 (SSO). The dielectric constant (epsilon (r)) and the dielectric loss (D) measurements were carried out on the as-quenched and heat-treated glass nanocomposite samples in the frequency range 100 Hz-10 MHz. The as-quenched and the heat-treated at two different temperatures (720 and 820 K) samples exhibited broad dielectric anomalies in the vicinity of the ferroelectric-to-paraelectric transition temperature of the parent BiV ceramics. The Curie-Weiss law was found to be valid at a temperature above the transition temperature, establishing the diffused nature of the transition

Structural and dielectric properties of ferroelectric Sr1−xBaxBi2(Nb0.5Ta0.5)2O9 and Sr0.5Ba0.5Bi2(Nb1−yTay)2O9 ceramics

Abstract Ferroelectric Sr 1− x Ba x Bi 2 (Nb 0.5 Ta 0.5 ) 2 O 9 and Sr 0.5 Ba 0.5 Bi 2 (Nb 1− y Ta y ) 2 O 9 were synthesized by solid state reaction route. X-ray diffraction studies confirm the formation of single phase layered perovskite solid solutions over a wide range of compositions ( x = y =0.0, 0.25, 0.50, 0.75 and 1). The lattice parameters and the Curie temperature ( T c ) have been found to have linear dependence on x and y . Transmission electron microscopy (TEM) suggest the lowering of orthorhombic distortion with increasing Ba 2+ substitution. Variations in microstructural features as a function of x and y were monitored by scanning electron microscopy (SEM). The dielectric constant at room temperature increases with increase in both x and y . Interestingly Ba 2+ substitution on Sr 2+ site induces diffused phase transition and diffuseness increases with increasing Ba 2+ concentration.