title: 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, 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).
authors: Materials Research Centre, Indian Institute of Science, Bangalore 560064, India.
authors: C
authors: C
authors: Karthik
authors: K B R
authors: KB
authors: Varma
mesh_terms: D017609:Barium Compounds / Q000737:chemistry; D001729:Bismuth / Q000737:chemistry; D001881:Borates / Q000737:chemistry; D004563:Electrochemistry; D005898:Glass / Q000737:chemistry*; D018020:Lithium Compounds / Q000737:chemistry; D053768:Metal Nanoparticles / Q000737:chemistry* / Q000648:ultrastructure; D008854:Microscopy, Electron; D053761:Nanocomposites / Q000737:chemistry* / Q000648:ultrastructure; D036103:Nanotechnology; D009556:Niobium / Q000737:chemistry; D010087:Oxides / Q000737:chemistry; D013053:Spectrophotometry; D013816:Thermodynamics; D014961:X-Ray Diffraction
chemical_list: D017609:Barium Compounds; D001881:Borates; D018020:Lithium Compounds; D010087:Oxides; D009556:Niobium; C077606:barium oxide; C033301:bismuth oxide; C021051:lithium borate; C073337:niobium pentoxide; D001729:Bismuth