Neutron diffraction study of the structure of chalcogen spinels Cu 1+yCr 2X 4 (X Se, Te)

Abstract

The structure of the copper excess chromium spinels Cu 2Cr 2Se 4 and Cu 1.81Cr 2Te 4 was determined by neutron diffraction at 300 K and at 4 K. The structure refinement reveals a simultaneous occupation of tetrahedral as well as of pseudo-octahedral sites by the excess y copper ions in Cu 1+yCr 2X 4. The relatively high temperature factors are discussed in terms of a specific local disorder model within the spinel space group Fd3m. From these results and the change in the lattice parameter α o with y a model was derived that is able to describe the sequence of occupation of tetrahedral and pseudo-octahedral lattice sites in the course of copper intercalation.