XPS study of transition metal doped silicate glasses

X-ray photoelectron spectroscopy (XPS) has been used to study the redox state of transition metal oxides in sodium silicate glasses with compositions 0.30Na₂O-0.70SiO₂ and 0.3Na₂O-0.6SiO₂-0.1TMO, where TMO = Fe₂O₃, CuO and CoO. From the analysis of the core level spectra of the transition metals, it was found that both Fe²⁺ and Fe³⁺ exist simultaneously in the iron doped glass, while Cu⁺ was the only species present in the copper doped glass. In the cobalt doped glass, Co²⁺ was found to exist in both tetrahedral (tet) and octahedral (oct) co-ordinations. From the analysis of the O 1s spectra, it was possible to discriminate between bridging and non-bridging oxygen atoms in each glass sample. It was also shown that the non-bridging oxygen contribution to the O 1s spectra can be simulated by summing the contributions from SiONa, SiOFe²⁺ and SiOFe³⁺ for the iron doped glass, SiONa and SiOCu⁺ for the copper doped glass and SiONa, SiOCo^2-(tet) and SiOCo²⁺(oct) for the cobalt doped glass. The quantitative values for the [Fe²⁺]/[Fe] and [Co²⁺(tet)]/[Co] concentrations ratios were found from the analysis of the Fe 3p and Co 3p core level spectra, respectively.