Structure and magnetic properties of lead vanadate glasses

Abstract

X-ray photoelectron spectroscopy (XPS) has been used to obtain structural information on the xPbO · (1− x)V 2O 5 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 O 1s 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 O 1s 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 Pb 4f 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 V 2p 3/2 peaks for the x<0.4 glasses indicate the presence of a small concentration of V 4+ ions in addition to V 5+ ions, while the symmetric V 2p 3/2 peaks for the more concentrated PbO vanadate glasses indicate only V 5+ 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 V 4+ ions, the susceptibility for these oxide glasses consisted of a positive, constant contribution arising from the temperature-independent paramagnetic V 2O 5 exceeding the diamagnetism from the core ions.