Structure of AgI-doped Ge–In–S glasses: Experiment, reverse Monte Carlo modelling, and density functional calculations

We report an investigation of the structure and vibrational modes of Ge–In–S–AgI bulk glasses using X-ray diffraction, EXAFS spectroscopy, Reverse Monte-Carlo (RMC) modelling, Raman spectroscopy, and density functional theoretical (DFT) calculations. The combination of these techniques made it possible to elucidate the short- and medium-range structural order of these glasses. Data interpretation revealed that the AgI-free glass structure is composed of a network where GeS4/2 tetrahedra are linked with trigonal InS3/2 units; S3/2Ge–GeS3/2 ethane-like species linked with InS4/2− tetrahedra form sub-structures which are dispersed in the network structure. The addition of AgI into the Ge–In–S glassy matrix causes appreciable structural changes, enriching the Indium species with Iodine terminal atoms. The existence of trigonal species InS2/2I and tetrahedral units InS3/2I− and InS2/2I2− is compatible with the EXAFS and RMC analysis. Their vibrational properties (harmonic frequencies and Raman activities) calculated by DFT are in very good agreement with the experimental values determined by Raman spectroscopy.