XPS and magnetic studies of vanadium tellurite glassses

A series of tellurite glasses containing vanadium with nominal composition xV₂O₅-(1 - x)TeO₂, where x = 0.1, 0.2, 0.3, and 0.4, have been prepared by melt quenching technique and investigated using X-ray photoelectron spectroscopy (XPS) and magnetization techniques. The Te 3d core level spectra show asymmetry and therefore were fitted with two contributions one from Te ions in TeO₄ trigonal bipyramid (tbp) configuration and the other from Te ions in TeO₃ trigonal pyramid (tp) configuration. Quantitative analysis of the areas of both components support the model of a change of TeO₄ tbp to TeO₃ tp upon V₂O₅ addition. The V 2p core level spectra did not show any asymmetry and were fitted with a single component corresponding to V⁵⁺ while the O 1s core level spectra show slight asymmetry on the higher binding energy side of the main peak and were fitted with two contributions, one due to bridging oxygen (BO) atoms and the other due to non-bridging oxygen (NBO) atoms. The fraction of NBO, determined from these spectra, is found to increase with increasing V₂O₅ content suggesting the formation of TeO₃ units and also that V₂O₅ is acting as a glass modifier in this glass series. The magnetic susceptibility data for these glasses follow a Curie-Weiss behavior (M/H = C/(T - θ)) 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 state V⁵⁺. The ratios of V⁴⁺/V_total as determined from magnetic susceptibility measurements assuming only the presence of magnetic V⁴⁺ and non-magnetic V⁵⁺ ions vary from 0.030 to 0.037. These ratios are too small to be detected by XPS measurements and this is why no asymmetry is observed in the V2p spectra of these glasses.