High resolution X-ray Photoelectron Spectroscopy (XPS) study of K2O-SiO2 glasses: Evidence for three types of O and at least two types of Si

High resolution O 1s, K 2p and Si 2p XPS Spectra were collected for a series of potassium silicate glasses ranging in composition from 10 mol% to 35 mol% K2O. The mole fraction of bridging oxygen (BO) has been accurately evaluated from the O is spectra. BO mole fractions of K-silicate glasses were calculated from Q-species distributions previously reported by Si-29 MAS NMR data. The mole fractions of BO are identical for the two techniques (within experimental error) in glasses containing 13 mol% to 25 mol% K2O but in the compositional range between 25 mol% and 35 mol% BO mole fractions obtained by XI'S are slightly greater than values derived from NMR data. The slight discrepancies between the two techniques at higher K2O content have not been resolved. The experimental data between 13 mol% and 25 mol% K2O indicate the presence of a third type of oxygen, O2-, in these glasses. A thermodynamic analysis indicates O2- is present at a few mol% in the glasses of low K2O content, but increases monotonically with increased K2O content. The O 1s XPS line widths for the BO peaks are highly variable. The variation in line widths may result from two types of BO contributing to the BO peak As in the Na2O-SiO2 glass system, one type probably bridges two Si atoms (Si-O-Si) and the second type is O bonded to two Si atoms and one K atom. The Si 2p XPS spectra are distinctly non-symmetric, with low binding energy shoulders commonly present on the major peak, suggesting two contributions to the Si 2p signal. There is a strong correlation of Si 2p XPS peak and shoulder intensities with the abundances of the Q(4) and Q(3) species in glasses of the same composition suggesting that, with additional resolution, XPS may be capable of resolving individual Q-species in this system. (C) 2011 Elsevier B.V. All rights reserved.