Free-volume defects and microstructure in ion-conducting Ag/AgI-As2S3 glasses as revealed from positron annihilation and microhardness measurements

The positron annihilation lifetime spectroscopy (PALS) study and load dependent Vickers microhardness data were applied together to find correlation between free-volume defects and microstructure in the pure As2S3 and metal-modified (As2S3)85Ag15 and (As2S3)85(AgI)15 glasses. The PALS data were analyzed by the well-developed formalism of the two-state positron trapping model while microhardness data were analyzed according to the strain-gradient plasticity theory presented in the form: H = H0(1 + d0/d), where H0 is the load independent hardness and d0 is a constant. Analysis of the experimental results showed that: (1) the hole-like defects with volume larger than or comparable with the size of the Ag+ ions but smaller than the size of the AgI clusters are present in the structure of the host glass matrix As2S3 and are effective positron traps, and (2) these free-volume defects determine the load-independent indentation microhardness H0 of a glass in the region of applied load where the HV decreases with an increase in the applied load P.