Phase Transitions in Ag₈SnSe₆ and Ag₈SnS₆: Mössbauer and X-ray Study

The structural transformations accompanying the low-temperature phase transition (PT) β´→γ in the argyrodite Ag8SnSe6 characterized by mixed electron-ionic conductivity, have been studied using nuclear gamma resonance (NGR) and X-ray diffraction (XRD). Parallel Mössbauer studies were performed on the structurally related canfieldite Ag8SnS6. An abrupt decrease in the probability of the Mössbauer effect and isomer shifts was observed in argyrodite and canfieldite near 356 K and 445 K, respectively, corresponding to phase transitions in these compounds. Spatial models of the first and second coordination spheres of Ag8SnSe6 in the β´ and γ-modifications have been proposed.