X-ray photoelectron spectroscopy (XPS) and FTIR studies of vanadium barium phosphate glasses

Barium vanadophosphate glasses, having composition 50BaO-xV(2)O(5)-(50 - x)P2O5, (x = 0-50 mol%), were prepared by conventional melt quench method. Density, molar volume and glass transition temperature (T-g) were measured as a function of V2O5 content. Structural investigation was done using XPS and FTIR spectroscopy. First, substitution of the P2O5 by the V2O5 in the metaphosphate 50BaO-50P(2)O(5) glass increases the density and T-g and decreases the molar volume. When the amount of V2O5 increases, all these properties show a reverse trend. XPS measurement found in the O1s, P2p, and V2p core level spectra indicate the presence of primarily P-O-P, P-O-V and V-O-V structural bonds, the asymmetry in the P 2p spectra indeed arises from the spin-orbit splitting of P 2p core level, and more than one valence state of V ions being present. IR spectroscopy reveals the depolymerization of the phosphate glass network by systematic conversion of metaphosphate chains into pyrophosphate groups and then orthophosphate groups. Even though metaphosphate to pyrophosphate conversion is taking place due to breaking of P-O-P linkages, formation of P-O-V and P-O-Ba linkages provide cross linking between short P-structural units, which make the glass network more rigid. Above 10-20 mol% V2O5 content, network is highly depolymerized due to the formation of orthophosphate units and V-O-V bridge bonds, resulting in poor cross-linking, making the glass network less rigid. (C) 2013 Elsevier B.V. All rights reserved.