THERMAL AND OPTICAL STUDIES OF MIXED ALKALI-ALKALINE EARTH OXIDE BORATE GLASSES (original) (raw)

Glasses with the composition xK2O-(25-x)Na 2O-12.5MgO-12.5BaO-50B 2O3 (x =0, 5, 10, 15, 20 and 25mol %) were synthesized by the melt-quenching technique and were characterized using X-ray diffraction technique at room temperature. Physical parameters like density, oxygen packing density, molar volume and glasstransition temperature and optical parameters, like direct, indirect band gap, cut -off wavelength and Urbach energy values were evaluated. These data was used to understand the mixed alkali effect in the glass matrix. Differential scanning calorimeter (DSC) was used to determine the glass-transition temperature (Tg ). From the optical absorption studies the values of the optical band gap (E opt ) for indirect transition, optical edge, cut-off wavelength, and Urbarch energy (∆E) have been evaluated. The values of Eopt, ∆E, glass-transition temperature and cut-off wavelength show nonlinear behavior with the K 2O content which may be due to mixed alkali effect. Density and molar volume also show nonlinear and opposite behavior with the K2O content which also may due to the mixed alkali effect in the present glass system. Keywords: Borate glasses, Differential scanning calorimeter (DSC), Optical absorption spectra, and mixed alkali effect