X-Ray photoelectron spectroscopy (XPS) studies of copper-sodium tellurite glasses

Sodium tellurite glasses containing CuO with the nominal composition [(Na2O)0.3(TeO2)0.7-x (CuO)x], where x=0.00, 0.05, 0.15, and 0.20, have been prepared and investigated by X-ray photoelectron spectroscopy (XPS). The binding energies of Te 3p, Te 3d, O 1s, and Cu 2p core levels in these glasses have been measured and compared to the corresponding binding energies in TeO2 and CuO powders. The Te 3p and Te 3d core levels for the glasses were essentially unchanged from those of TeO2 powder and have little dependence upon the CuO content. Although the O 1s peak showed a small asymmetry on the higher energy side of the peak in the glasses, it was primarily the result of hydroxide contamination on the glass surface rather than the appearance of non-bridging oxygen atoms arising from a structural change in the TeO4. For glasses with x=0.05 and 0.15, the Cu 2p peaks were shifted by more than 1 eV towards lower binding energies in comparison to their values in CuO powder, which suggests the presence of Cu+ ions in these glasses. The appearance of satellite peaks in the Cu 2p spectra, however, provided definitive evidence for the presence of Cu2+ ions in these glass samples as well. The broadened Cu 2p3/2 peaks were correspondingly decomposed into two distinct peaks separated by approximately 1.25 eV, with the lower energy peak being associated with Cu+ and the higher one with Cu2+. The relative Cu2+ content estimated from the spectral analysis was found to vary from 15% for the x=0.05 glass sample to over 70% for the x=0.20 sample