X-ray study of the average structures of Cu2Se and Cu1.8S in the room temperature and the high temperature phases

The structures of the antifluorite-type copper chalcogenides Cu2Se and Cu1.8S 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 Cu2Se and Cu1.8S. Contrary to the recent EXAFS analysis, however, this site is populated in the high temperature phase of Cu2Se. From the population data, the drift pathway of copper ions was discussed.