Structure and magnetic properties of lead vanadate glasses

X-ray photoelectron spectroscopy (XPS) has been used to obtain structural information on the xPbO·(1-x)V₂O₅ glass system where x=0.22, 0.35, 0.43, and 0.54. The binding energies from the Pb 4f _7/2 and Pb 4f_5/2 core levels decrease with increasing PbO content while the full-width at half-maximum of these peaks increase. The O1s spectra show an asymmetry for samples having composition x<0.5, which results from oxygen atoms in the V-O-V configuration (bridging oxygens) and from oxygen atoms in the V-O-Pb and Pb-O-Pb configurations (non-bridging oxygens). The number of non-bridging oxygens was found to increase from 81% to 92% with increasing PbO content. For x=0.54, the O1s spectrum was symmetric indicating that all three oxygen configurations have essentially the same binding energy. This behavior in addition to the decreasing binding energies of the Pb4f levels with increasing PbO content suggest that the Pb-O bonds are becoming more covalent in nature and that eventually PbO changed its role from a glass modifier to a glass former for x>0.5. The asymmetric V2p _3/2 peaks for the x<0.4 glasses indicate the presence of a small concentration of V⁴⁺ ions in addition to V⁵⁺ ions, while the symmetric V2p_3/2 peaks for the more concentrated PbO vanadate glasses indicate only V⁵⁺ being present. The concentration of V ⁴⁺ ions (0-4%) from the XPS data is consistent with determinations from magnetic susceptibility measurements on the same glass samples. In addition to the paramagnetic contribution (Curie-Weiss temperature-dependent behavior) from the V⁴⁺ ions, the susceptibility for these oxide glasses consisted of a positive, constant contribution arising from the temperature-independent paramagnetic V₂O₅ exceeding the diamagnetism from the core ions.