Electron paramagnetic resonance and thermal behavior of vanadyl-doped mixed alkali bismuth borate glasses

Glasses with composition 15 Li2O15K2O10Bi2O3(60 − x) B2O3: xV2O5 where x = 1, 3, 5, 7, and 9 mol% are prepared by normal melt-quench technique. Characterization of the prepared samples is done using X-ray diffraction, density and differential scanning calorimetry. The density and molar volume are found to increase with increasing x whereas the glass transition temperature decreases. Electron paramagnetic resonance spectra of the prepared samples are recorded using EPR-spectrometer operating in the X-band frequency. The resonance spectra are well resolved for x ≥ 5 mol% and the intensity of the resonance peak is found to increase with increasing x. The values of spin-Hamiltonian parameters (SHP) and molecular orbital coefficients are evaluated. From the values of SHPs it is concluded that V4+ ions in the present glass system exist as vanadyl ions in octahedral co-ordination with tetragonal compression. It is observed that the SPHs depend slightly on the relative concentration of V2O5. Further, the theoretical optical basicity of the glasses has also been evaluated and it is observed that the changes in optical basicity values are in accordance with the changes in SHPs.