X-ray photoelectron spectroscopy (XPS) and magnetic susceptibility studies of vanadium phosphate glasses

Vanadium phosphate glasses with the nominal chemical composition [(V₂O₅)_x(P₂O₅)_1-x], where x = 0.30, 0.40, 0.50, and 0.60, have been prepared and investigated by X-ray photoelectron spectroscopy (XPS) and magnetization measurements. Asymmetries found in the O 1s, P 2p, and V 2p core level spectra indicate the presence of primarily P-O-P, P-O-V, and V-O-V structural bonds, a spin-orbit splitting of the P 2p core level, and more than one valence state of V ions being present. The magnetic susceptibility data for these glasses follow a Curie-Weiss behavior which also indicates the presence of some V ions existing in a magnetic state, i.e., a valence state other than that of the non-magnetic V⁵⁺. From qualitative comparisons of the abundance of the bridging oxygen or P-O-P sites as determined from the areas under the various O 1s peaks with the abundances of differing phosphate structural groups associated with the presence of different valence states of the vanadium ions, a glass structure model consisting of a mixture of vanadate phosphate phases is proposed for these glass samples. These include V₂O₅, VOPO₄, (VO)₂P₂O₇, VO(PO₃), and V(PO₃)₃ with the abundance of orthophosphate (PO₄)^3- units increasing with increasing vanadium content.