Synthesis, structure and physical property of Ag_3AsS_3-Ag_3AsSe_3

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Ag_3 AsS_3 (proustite) - Ag_3 SbS_3 (pyrargyrite) solid solution and Ag_3 AsSe_3, which was first synthesized in our Department,are isostructural, and Ag atoms in these end member crystals, show large anisotropic thermal vibrations. Recently Kihara and Matsumoto have refined the crystal structure of Ag_3 AsSe_3 using anharmonic thermal vibrations and suggested the ionic conductivity and this property has been confirmed by Yoshiasa. In this project, we continue to investigate these crystals and glass in detail, using x-ray diffraction method and EXAFS measurement. The main results are as follows.1. Ag_3 (As,Sb)S_3 solid solution. Seven crystalline substances with different composition were prepared by silica-glass quenching method,and x-ray absorption spectra were collected for As and Sb K absorption edges and |F(r)|'s of k chi(k) for these EXAFS spectra were obtained. All prominent peaks corresponding to As-S and Sb-S are similar position for 7 samples with different height. This fact suggests AsS_3 and SbS_3 groups exist separately in this series. 2. Ag_3 As S_3 glass. The local structure of this glass has been investigated by EXAFS analysis. The local structure around As atom is very similar to that in the crystal, and this suggests AsS_3 groups exist in glass as in crystal.The Ag-S distances in the glass are almost equal to that of crystal, but because of weak intensity and large Debye-Waller type factor, Ag atoms randomly distribute around AsS_3 groups, and this suggests that Ag atoms contribute to the ionic conduction.