Local structure and redox state of vanadium in strontium-vanadate glasses

The local structure of vanadate glasses containing SrO with the nominal composition [(SrO)_x (V₂O5)_1-x], where 0.2 ≤ x ≤ 0.5, have been investigated by X-ray photoelectron spectroscopy (XPS). The core-level binding energies of V 2p, Sr 3p and O 1s have been measured. The doublet peaks attributed to Sr 3p_3/2 and Sr 3p_1/2 in the Sr 3p spectra have essentially the same binding energies for all glass samples, regardless of the composition The O 1s core level spectra, however, show slight asymmetry for the glass samples with x = 0.2 and 0.3 which results from two contributions, one from the presence of oxygen atoms in the V-O-V environment called bridging oxygen (BO) and the other from oxygen atoms in an Sr-O-V and V = O environment called non-bridging oxygen (NBO). For samples with x = 0.4 and 0.5 the O 1s spectra were symmetric indicating the existence of only one type of oxygen configuration (NBO). There is a good agreement between the measured (XPS) and calculated values for NBO/TO. The quantitative ratio, [V ⁴⁺/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.