OPTICAL PROPERTIES AND CHEMICAL BONDING OF TiO2-BaO-V2O5 GLASSES
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2016-01-01
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Abstract
Glasses of compositions xTiO2.(35-x)BaO.65V2O5 (x=0, 1, 3, 5, 10, 15 and 20 mol %) are prepared using the conventional melt quenching method. XRD, DTA and DSC analysis are performed. The XRD results confirm the amorphous nature of the samples. The ternary glasses show low glass transition temperatures, Tg, of 228°C - 253°C and crystallization temperatures, Tx, of 266°C - 323°C. The density measured decreases with increase of TiO2 content from 3.542 g cm-3 to 3.287 g cm-3. The theoretical refractive index, the electronic oxide ion polarizability, the optical basicity and the optical band gap of the glasses are calculated by the Lorentz-Lorenz equation. The glasses are found to possess a high refractive index (2.169 - 2.236), a comparatively narrow band gap (4.01 eV - 3.67 eV), high electronic ion polarizability (2.650 Å3 - 2.722 Å3) and high optical basicity (1.040 - 1.057). The third order nonlinear optical susceptibility χ(3) is determined by the generalized Miller’s rule and the three photon model. It is found that χ(3) values are in the 0.76 - 1.1 x10-12 esu range. The average single bond strength BM-O and the interaction parameter A(no) are calculated. The bond strength is found to vary from 253 kJ mol-1 to 285 kJ mol-1, while the interaction parameter is in the 0.050 Å-3 - 0.055 Å-3 range, thus suggesting the presence of weak chemical bonds. The presence of such bonds, namely Ba…O=V, V-NBO (nonbridging oxygen), V-O-Ti and V-O-V is verified by the glasses IR-spectra. The high polarizability of the oxide ions in these bonds accounts for the observed linear and nonlinear optical properties of the glasses. A structural model of glasses containing VO5, VO4 and TiO4 groups is advanced.