Les composes Ag7AsS6 et Ag7AsSe6 etude des proprietes thermiques,cristallographiques et electriques

The preparation and the partial phase diagrams Ag₂X“As₂X₅” (X = S or Se) are described. Peritectic decompositions occur at 560°C for Ag₇AsS₆ and 360°C for Ag₇AsSe₆. Phase changes are observed at 250°C for Ag₇AsS₆ and 150°C for Ag₇AsSe₆. For each compound, the low temperature form is cubic P2₁3, and the high temperature form has the Ag₈GeTe₆ structural type, F$\text{4}$3m. The high temperature forms are not quenchable. Ionic and electronic conductivity have been measured in Ag₇AsS₆ and Ag₇AsSe₆. Ionic conductivity was measured using RbAg₄I₅ as a blocking electrode for electronic conduction. Electromotive force measurements confirm transference numbers. At room temperature, ionic conductivities were 1,5.10^?6 (Ω.cm)^?1 and 0,08 (Ω.cm)^?1 for Ag₇AsS₆ and Ag₇AsSe₆ respectively.