Extended x-ray absorption fine structure and molecular dynamics simulation studies on the structure of CuX- and AgX-based glasses (X = Cl, Br and I)

Extended x-ray absorption fine structure (EXAFS) spectra at the Cu K-edge and Ag K-edge were measured for copper(I) halide-based and silver halide-based glasses, respectively. Molecular dynamics (MD) simulation was also performed for the glasses with the same compositions. The bond distances, A-X, in the copper(I) halide-based and the AgI-based glasses, which were obtained from the EXAFS analyses, were almost the same as those in the CuX (X = Cl, Br, I) and AgI crystals. The coordination numbers of halide ions around the monovalent metal ions were nearly four as well as those in the crystals. These results were consistent with those of the MD simulation. On the other hand, the EXAFS analyses showed that the bond distances in the AgCl-based and the AgBr-based glasses were 0.1 Å shorter than those in the AgCl and AgBr crystals. These values are in the range of those of the halogenoargentate crystals having three- or fourfold coordination. However, the coordination numbers obtained from the EXAFS analyses were larger than four. The MD simulation suggested that the coordination shells in the AgCl-based and the AgBr-based glasses are highly disordered.