Ionic Conduction and Local Structure in AgI-As2Se3 Glasses

Glassy (AgI)(40)(As2Se3)(60) samples were successfully obtained by the mechanical milling method using starting powder mixtures of crystalline AgI, arsenic and selenium. Glass transition phenomena were clearly observed in the XRD and DSC signals during the progress of amorphization. The conductivity increased rapidly at the early period of the milling (0.5 - 2 hours). After that, (AgI)(40)(As2Se3)(60) samples showed gradual decrease in the conductivity with increasing milling time. It was found that the ion transport number was approximately unity at the whole milling stage. To investigate the milling time dependences of the environmental structure around constituent atoms, the EXAFS measurements at As, Se, Ag, I K-edges for (AgI)(40)(As2Se3)(60) samples at different milling periods were carried out at the Photon Factory -KEK (Tsukuba, Japan). The apparent decrease of coordination number of Ag-I pairs was observed. It could be considered that the most suitable local structure around Ag ions might be required to the fast ionic conduction in the AgI-doped As-chalcogenide system.