Electronic structure of thiogermanate and thioarseniate glasses: experimental (XPS) and theoretical (ab initio) characterizations

The paper reports on structural investigation and electronic structure of thiogermanate and thioarseniate glasses by means of X-ray photoelectron spectroscopy (XPS) and ab initio calculation. Besides an increase of nonbridging sulfur (nbS) when increasing the amount of modifier (Ag2S), a limit in the breakdown between nbS and bridging sulfur (bS) atoms was observed for the intermediate Ag concentrations in the two families for the silver containing glasses. The influence of the modifier cation has been studied for the M2GeS3 glass family (M=Ag, Li, Na). Compared to alkali glasses, a more homogeneous electronic distribution on sulfur atoms was observed for Ag2GeS3. Furthermore, the electronic redistribution along Ge–S bonds is the most important in the case of Na2GeS3. In agreement with XPS results, Mulliken population analysis showed only a small difference (more important for Na than for Ag) between the charges on bS and nbS. According to XPS data (valence band), ab initio calculations on cluster models showed important changes—compared to GeS2—in both Ge–S and Ge–Ge interactions, and support the concept of a nonlocalized effect of alkali-metal atoms.