X-ray photoelectron study of Te-W-O and Te-W-La-O glasses

Abstract

The elemental and ionic surface compositions of (TeO2)0.8 (WO3)0.2 and (TeO2)0.7(WO3)0.2(La2O3)0.1 glasses annealed at different temperatures and bombarded with Ar+ ions for various lengths of time have been determined using x-ray photoelectron spectroscopy. The results indicate that the surface layer of the glasses contains tellurium ions in two chemical states, which differ markedly in concentration. The oxidation state of one type of tellurium ion is close to that in TeO, \(E_{b_1 } \) (Te 3d5/2)= 574.0 eV, and the oxidation state of the other is close to that in TeO2 [\(E_{b_2 } \) (Te 3d5/2) = 576.6 eV. In all of the samples, tungsten is in an oxidation state close to 6+ (WO3), and the oxidation state of lanthanum is 3+ (La2O3). Ar+-ion milling for 4 min using an argon gun markedly reduces the surface hydrocarbon contamination but has, for the most part, an insignificant effect on the characteristics of the XPS spectra. Increasing the ion milling time leads to the formation of new states of both tellurium and tungsten ions. The oxygen ions in the glass samples studied are chemically equivalent and differ markedly in oxidation state from those in the constituent metal oxides. The metal—oxygen bond length evaluated from the O 1s binding energy in the glasses is RM-O = 0.192 nm.