Phase evolution, characterization, and impedance spectroscopic analysis of nanocrystalline SrBi2Nb2O9 in glassy Li2B4O7 matrix.

Transparent glass composites in the system (100 - x) Li2B4O7 - x SrBi2Nb2O9 (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 SrBi2Nb2O9 (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 Li2B4O7 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.