Thermal, structural, optical, and dielectric properties of (100 - x)Li2B4O7 - x(BaO-Bi2O3-Nb2O5) glasses and glass-nanocrystal composites.

C Karthik, K B R Varma

Index: J. Nanosci. Nanotechnol. 7(3) , 1006-13, (2007)

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Abstract

Transparent glasses in the system (100 - x)Li2B4O7 - x(BaO-Bi2O3-Nb2O5) (x = 10, 20, and 30) were fabricated via the conventional melt-quenching technique. The amorphous and glassy characteristics of the as-quenched samples were established by the differential thermal analyses (DTA) and X-ray powder diffraction (XRD) studies. Glass-nanocrystal composites (GNCs) i.e., the glasses embedded with BaBi2Nb2O9 (BBN) nanocrystals (10-50 nm) were produced by heat-treating the as-quenched glasses at temperatures higher than 500 degrees C. Perovskite BBN phase formation through an intermediate fluorite-like phase in the glass matrix was confirmed via XRD and transmission electron microscopic (TEM) studies. The optical transmission properties of these GNCs were found to have a strong compositional (BBN content) dependence. The refractive index (n = 1.90) and optical polarizability (alphao = 15.3 x 10(-24) cm3) of the GNC (x = 30) were larger than those of as-quenched glasses. The temperature dependent dielectric constant (epsilonr) and loss factor (D) for the glasses and GNCs were determined in the 100-40 MHz frequency range. The epsilonr was found to increase with increase in heat-treatment temperatures, while the loss of the glass-nanocomposites was less than that of as-quenched glasses. The sample heat-treated at 620 degrees C/1 h (x = 30) exhibited relaxor behavior associated with a dielectric anomaly in the 150-250 degrees C temperature range. The frequency dependence of the dielectric maximum temperature was found to obey the Vogel-Fulcher relation (Ea = 0.32 eV and Tf = 201 K).