Synthesis, structure and physical property of Ag_3AsS_3-Ag_3AsSe_3

Ag_3AsS_3（proustite）-Ag_3SbS_3（pyrargyrite）固溶体和我们首次合成的Ag_3AsSe_3是同构的，这些端员晶体中的Ag原子表现出大的各向异性热振动。最近Kihara和松本利用非谐热振动对Ag_3AsSe_3的晶体结构进行了修正，提出了离子导电性的概念，并得到了Yoshiasa的证实。在这个项目中，我们继续详细研究这些晶体和玻璃，使用X射线衍射方法和EXAFS测量。主要研究结果如下：1. Ag_3（As，Sb）S_3固溶体。用石英玻璃淬冷法制备了7种不同组成的晶体物质，收集了As和Sb的K吸收边和K吸收边的X射线吸收谱，|F（r）|得到了这些EXAFS谱的kchi（k）的值。7个不同高度的样品中，As-S和Sb-S的主峰位置均相似。这一事实表明AsS_3和SbS_3基团在该系列中是分开存在的。2. Ag_3As S_3玻璃。用EXAFS分析了该玻璃的局域结构。As原子周围的局域结构与晶体中的结构非常相似，说明玻璃中存在AsS_3基团，玻璃中的Ag-S距离与晶体中的Ag-S距离几乎相等，但由于强度较弱，Debye-Waller型因子较大，Ag原子随机分布在AsS_3基团周围，说明Ag原子对离子导电有贡献。

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.