An EXAFS Study of Coordination of Ag in AgI-Ag2O-GeO2 Glasses

Local structures around Ag+ ions in ion-conducting glasses in the system AgI-Ag2O-GeO2 were investigated by Ag K EXAFS (extended X-ray absorption fine structure) analysis. By using Ag2O and AgI crystals as reference samples, average Ag-O and Ag-I distances for three kinds of glass samples were estimated from |F(r)| curves to be 2.15-2.22Å and 2.74-2.87Å, respectively. The Ag-O atomic distances suggest that a part of Ag+ ions locate near the polygermanate anions which consisted of GeO4 tetrahedra. As the Ag+ ions of this type are strongly bonded to O2- ions, they do not contribute to the ionic conduction. It was also concluded on the basis of the Ag-I atomic distances that the rest of Ag+ ions locate at tetrahedral sites surrounded by four I- ions. Since the coodinations of these Ag+ ions are similar to those of Ag+ ions in AgI crystals which show ionic conductivity, the Ag+ ions of this type contribute to the ionic conduction.