Local structure and redox state of vanadium in vanadium strontium borate [(V2O5)(0 center dot 5)(SrO)(0 center dot 5)(SrO)(0 center dot 5-y)(B2O3)(y)] oxide glasses

The local structure of vanadium strontium borate glasses with the nominal composition [(V2O5)(0.5)(SrO)(0.5-y) (B2O3)y], where 0.1 <= y <= 0.4, as well as the valence state of the vanadium ions have been investigated by x-ray photoelectron spectroscopy (XPS). The core level binding energies of V 2p, Sr 3p, B Is and 0 Is have been measured. It was observed that there is a small increase in binding energies of the doublet peaks attributed to Sr 3p(3/2) and Sr 3p(1/2) in the Sr 3p spectra with an increase in the B2O3 content and also shifted by similar to 0-6 eV towards higher binding energies in comparison to their values in SrO powder The binding energies of the B 1s peak positions increase with an increase in the B2O3 content, have essentially the same FWHM but, in comparison to B2O3 powder, the peak positions have shifted towards lower binding energy side by similar to 0.7 e V The 0 Is core level spectra, however show asymmetry for all glass samples which results from two contributions, one from the presence of oxygen atoms in the V-O-V V-O-B, B-O-B environment (bridging oxygen BO) and the other from oxygen atoms in V-O-Sr, B-O-Sr V=O, environment (non-bridging oxygen NBO). The O 1s core level spectra were deconvoluted into two peaks (BO and NBO) and the ratio of NBO to total oxygen was found to decrease with increasing B2O3 content. The quantitative ratio, [V4+/V-total], for each glass sample, has been determined from the analysis of the V 2p core level spectra. The ratio remains practically constant, independent of vanadium concentration within experimental uncertainties.