Phase Evolution, Characterization, and Impedance Spectroscopic Analysis of Nanocrystalline $SrBi_2Nb_2O_9$ in Glassy $Li_2B_4O_7$ Matrix

Abstract

Transparent glass composites in the system $(100 - x)Li_2B_4O_7 - xSrBi_2Nb_2O_9$ (where x = 5, 10, 15, 20, 25, and 30, in molar ratio) were fabricated by conventional melt-quenching technique. The amorphous nature of the as-quenched glass composites was confirmed via X-ray powder diffraction (XRD) studies. Differential thermal analyses (DTA) established the glassy nature of the as-quenched samples. Glass nanocomposites (GNC's) with high-optical transparency were obtained by controlled heat-treatment of the glass composites at 750 K/6 h. Perovskite $SrBi_2Nb_2O_9$ (SBN) phase formation through an intermediate fluorite phase was confirmed by XRD and transmission electron microscopy (TEM). The dielectric constant $(\epsilon_r)$ in the frequency range from 100 Hz to 40 MHz at room temperature increases whereas dielectric loss (D) decreases with increase in SBN content in $Li_2B_4O_7$ glass matrix. Impedance spectroscopy employed to rationalize the electrical behavior of the as-quenched glasses and glass nanocomposites suggests the coexistence of electronic and ionic conduction in these materials. The optical transmission and band-gap energy of these composites were found to be crystallite size dependent