LOW-TEMPERATURE CUBIC-TETRAGONAL PHASE-TRANSITION IN CUV2S4 SPINEL COMPOUND

The low-temperature X-ray diffraction study and the magnetization and the electrical resistivity measurements, were performed on the single phase polycrystalline spinel CuV2S4. The crystal structure was confirm ed to have a normal cubic spinel structure with a=9.809 A and u=0.382 at 300 K. The splitting of the (400) plane was observed below 90 K, re sulting in the coherent cubic to tetragonal phase transition with c/a= 0.997. Any additional lines due to the charge density wave were not ob served. The tetragonality c/a and the deformation potential of spinels fairly well explained the transition temperature of 90 K and the spli tting of the 3d(d epsilon) orbit of about 15 meV. Thus, the phase tran sition is explained by the cooperative Jahn-Teller effect of V3+(3d(2) ) in the octahedral site.