Crystal Structure Determination of Ag₃CuS₂ From Powder X-Ray Diffraction Data

Abstract

The crystal structure of Ag₃CuS₂ has been determined by using X-ray powder diffraction data. The unit cell is tetragonal, a = 8.6705(10), c = 11.7573(18) Å , and the space group is I4₁/amd (141) with Z = 8. A starting model for the structure was derived by using direct methods and difference Fourier cycling from 93 unambiguously indexed integrated intensities, and then refined by the Rietveld method. Both diffractometer and Guinier-Hagg data were utilized. Corroborative evidence for the correctness of the resulting structure was obtained by comparison of experimental and calculated single-crystal electron diffraction intensities.

The Ag₃CuS₂ structure is based on distorted bcc sulfur packing. There are two distinct silver sites. In one the silver atom is surrounded by six sulfur atoms forming a [2+4] distorted octahedral environment. In the other site the silver atom is in a distorted tetrahedral environment with two sulfur atoms nearby and two more, somewhat farther away. Copper is linearly coordinated by two sulfur atoms.