Twin Structure of NiCr₂O₄ Single Crystal Due to Cooperative Jahn-Teller Distortion

Abstract

The tetragonal phase of nickel chromite (NiCr₂O₄) was investigated by X-ray diffraction method for single crystal. The {110} twin structure was found, below the transition temperature (29°C), as a result of the tetragonal domain formation due to the Jahn-Teller distortion. The twin angle was observed to vary in accord with the temperature dependence of c/a and to be about 1.1° and 1.6° at T=21°C and T=−30°C, respectively.