Electronic polarizability, optical basicity and XPS spectra of Sb₂O₃-B₂O₃ glasses

The average electronic polarizability of the oxide ion (α_O(2-)) and optical basicity (Λ) of Sb₂O₃-B₂O₃ glasses have been estimated from the values of refractive index and optical band gap, and the O1s and Sb3d binding energies have been measured from X-ray photoelectron spectroscopy (XPS) spectra in order to clarify the electronic structure of oxide glasses. Both α_O(2-) and Λ increase with increasing Sb₂O₃ content and conversely both O1s and Sb3d binding energies decrease. Close correlations are observed among them, and particularly it has been confirmed that the O1s binding energy is a good measure of the optical basicity of these glasses. The O1s signal in XPS spectra consists of two components: the O1s peak with higher binding energies is assigned to B-O-B bonds and that with lower binding energies corresponds to Sb-O-B and Sb-O-Sb bonds. It has been also suggested that a substantial rearrangement in the bridging oxygen bonding takes place at about 40 mol% Sb₂O₃: with a decrease in the number of B-O-B bonds and an increase in the number of Sb-O-B and Sb-O-Sb bonds. The covalency of Sb-O bonds increases with increasing Sb₂O₃ content, and its origin has been discussed in view of the good correlation between O1s and Sb3d binding energies, suggesting the formation of Sb-O bonds rich in p-character due to the increased probability of back donation of electron density from O^2- to Sb³⁺ ions.