X-Ray Photoelectron Spectroscopy of Alkali Silicate Glasses

Abstract

X-ray photoelectron spectra were measured on the fresh surfaces of silica, binary alkali silicate and mixed alkali silicate glasses fractured in ultra-high vacuum by irradiating with focusing monochromatic AlKα X-ray. Binding energies and chemical shifts of O1s, Si2p, Li1s, Na1s, K2p, Rb3d5/2 and Cs4d5/2 have been investigated, and charge densities of oxide, silicon and other alkali ions have been discussed. For xNa2O⋅(100-x)SiO2 glasses, electron densities of bridging oxide ion (BO), non-bridging oxide ion (NBO) and sodium ions increased with increasing the Na2O content, suggesting that the bond order between O2p and Na3s (or 3p) increased with increasing the Na2O content. In addition, the difference in binding energies between BO1s and NBO1s decreased with increasing Na2O content indicating that electrons were delocalized considerably in O2p-Si3d π bonds. For 33.3R2O⋅66.7SiO2 (R=Li, Na, K, Rb, Cs) glasses, charge densities of BO increased with increasing ionic radius of alkali ions (Li→Na→K, Rb→Cs). The degree of polarization of BO increased with increasing ionic radius of alkali ions. For 33.3{(1-y)Li2O⋅yCs2O}⋅66.7SiO2 glasses, O1s peak of NBO could not been discriminated between the components belonging to Si-O-…Li+ and Si-O-…Cs+. O1s chemical shifts of 33.3{(1-x)Li2O⋅xCs2O}⋅66.7SiO2 glasses with increasing Cs2O content were similar to the shifts of 33.3R2O⋅66.7SiO2 glasses with increasing ionic radius of alkali ions. The area-weighed mean values of O1s peaks appeared to have good correlation with an empirical expression of optical basicity.