Thermal, Structural, Optical, and Dielectric Properties of (100 − x)Li2B4O7 − x(BaO-Bi2O3-Nb2O5) Glasses and Glass-Nanocrystal Composites
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 (α o = 15.3 × 10−24 cm3) of the GNC (x = 30) were larger than those of as-quenched glasses. The temperature dependent dielectric constant (ε r) and loss factor (D) for the glasses and GNCs were determined in the 100–40 MHz frequency range. Theε r 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 (E a = 0.32 eV and T f = 201 K).
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Document Type: Research Article
Publication date: 01 March 2007
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