Thermal, Structural, Optical, and Dielectric Properties of (100 − x)Li2B4O7 − x(BaO-Bi2O3-Nb2O5) Glasses and Glass-Nanocrystal Composites
Abstract:Transparent glasses in the system (100 − x)Li2B4O7 − x(BaO-Bi2O3-Nb2O5) (x = 10, 20, and30) 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 °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 (αo = 15.3 × 10−24 cm3) of the GNC (x = 30) were larger than those of as-quenched glasses. The temperature dependent dielectric constant (r) and loss factor (D) for the glasses and GNCs were determined in the 100–40 MHz frequency range. Ther 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 °C/1 h (x = 30) exhibited relaxor behavior associated with a dielectric anomaly in the 150–250 °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).
Document Type: Research Article
Publication date: March 1, 2007
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