High temperature X-ray diffraction studies on Cr-doped V₂O₃

Abstract

X ray powder diffraction on high purity (Cr_0.01V_0.99)₂O₃ and (Cr_0.033V_0.967)₂O₃ prepared by the arc-melting technique has been carried out in the temperature range of room temperature to 500° C. The room temperature rhombohedral structure of (Cr_0.01V_0.99)₂O₃ is found to undergo, in agreement with earlier results, a gradual transition to an isomorphous, high-temperature rhombohedral structure over a temperature range of 50-200° C. The percentage of the two phases in this coexistence range has been determined at different temperatures from the relative X ray intensities. This is found to depend on the thermal history of the sample and shows considerable hysteresis between heating and cooling cycles. Annealing of the material at 1600° C is found to stabilize the low temperature form and to broaden the temperature region of the transition. The temperature interval of the electrical anomaly correlates well with the two-phase interval. The lattice parameters and their temperature coefficients have been determined for all the phases.