X-ray study of the average structures of Cu 2Se and Cu 1.8S in the room temperature and the high temperature phases

Abstract

The structures of the antifluorite-type copper chalcogenides Cu 2Se and Cu 1.8S were studied using single crystal X-ray diffraction data both below and above the transition point. Using the cubic indexing main reflections, the average structures of the compounds were refined by least squares methods: a facecentered arrangement of the chalcogen atoms was assumed and copper atoms were distributed at the tetrahedral, trigonal, and octahedral interstitial sites, and their relative populations were refined. The tetrahedral and trigonal sites are populated by copper atoms at both room temperature and high temperature phases. The octahedral site is not populated in the room temperature phase of either Cu 2Se and Cu 1.8S. Contrary to the recent EXAFS analysis, however, this site is populated in the high temperature phase of Cu 2Se. From the population data, the drift pathway of copper ions was discussed.