Correlation between the high temperature anomalies in V2O3 and the lattice parameters

A single phase corundum type structure was observed in V₂O₃ from 165 to 1100K. An anomalous behaviour of the lattice parameters of the rhombohedral unit cell was found in the high temperature region where V₂O₃ undergoes a broad electrical transition. The unit cell edge a_R contracts above 165 K, reaching a minimum at 533 K, after which there is a sharp increase. Above 595 Ka_R expands continuously and then almost linearly above 775 K. The temperature dependence of the rhombohedral angle shows two distinct regions, and the volume expansion follows the variation of angle; the change of the rate of expansion coincides with the minimum of a_R. The contraction of a_R corresponds to a reduction in certain second-neighbor VV distances.Our results show that a gradual transition is taking place in V₂O₃ from an α type structure to a β type characteristic of the Cr-doped V₂O₃ compounds. In addition, the sharp dip of the a_R curve occurs at nearly the same temperature as the peak previously observed in small angle scattering of neutrons. It is presumed that the two effects are related, and that the critical-like behaviour of a_R is due to some dynamic magnetoelastic effect involving second neighbor VV interactions.