XANES and XPS investigations of the local structure and final-state effects in amorphous metal silicates: (ZrO2)x(TiO2)y(SiO2)1−x−y

Abstract

Amorphous quaternary [(ZrO₂)_x(TiO₂)_y(SiO₂)_1−x−y] and ternary [(ZrO₂)_x(SiO₂)_1−x] silicates were synthesized using a sol–gel method and examined viaXPS and XANES. Metal silicates are important industrial materials, though structural characterization is complicated because of their amorphous nature. Hard (Ti K- and Zr K-edge) and soft (Ti L_2,3-edge) X-ray XANES spectra suggest the Ti and Zr coordination numbers in the quaternary silicates remain constant as the metal identity or total metal content (x, y, or x + y in the chemical formula) is varied. XPS core-line spectra from the quaternary silicates show large decreases in Ti 2p_3/2, Zr 3d_5/2, Si 2p_3/2, and O 1s binding energies due to increasing final-state relaxation with greater next-nearest neighbour substitution of Si for less-electronegative Ti/Zr, which was confirmed by analysis of the O Auger parameter. These decreases in binding energy occur without any changes in the ground-state energies (e.g., oxidation state) of these atoms, as examined by Ti L_2,3-edge, Si L_2,3-edge, and O K-edge XANES. Because most spectroscopic investigations are concerned with ground-state properties, knowledge of the contributions from final-state effects is important to understand the spectra from materials of interest.