Single crystal growth, structure refinement, ferroelastic domains and phase transitions of the hausmannite CuCr₂O₄

With a view to studying the optical, structural and magnetoelec. properties, single crystals of the hausmannite CuCr2O4 were grown by a high temp. soln. method, based on the thermal decompn. of K2Cr2O7 in the presence of CuO. X-ray powder refinements at room temp. indicate that the crystal structure of CuCr2O4 can be accurately described by the centrosym. space group I41/amd. Crystal cuts were examd. by polarized light microscopy in reflection, revealing ferroelastic domain structures consistent with the tetragonal symmetry. The phase transitions in the Cu chromite were studied both by in situ optical domain observations and by DTA and DSC measurements. The ferroelastic phase transition from the tetragonal to the cubic phase was found to take place at 853 K and to be of 1st order. The magnetic phase transition was revealed by a DSC peak at 157 K with a small enthalpy of 0.2 J/g. Crystallog. data and at. coordinates are given