Crystal Structure of the Low-Temperature Antiferromagnetic Phase ofV2O3

At ∼ 155 °K, the metallic corundum structure of ${\mathrm{V}}_2$ ${\mathrm{O}}_3$ distorts to an insulating monoclinic one. Structural refinements of this low-temperature phase by x-ray diffraction techniques show an increase in the nearest-neighbor vanadium — vanadium distances at the transition. This is in direct contrast to previously reported distortion models. In the $a-c$ plane of the monoclinic structure, the vanadium — vanadium distance across the shared octahedral face increases from 2.697 to 2.745 ∼, while the vanadium — vanadium distance across the shared octahedral edge increases from 2.882 to 2.987 ∼ when proceeding from the corundum structure to the monoclinic one. The oxygen octahedra become skewed about the central vanadium atom, while the average vanadium — oxygen distance remains essentially constant. The expansion of the vanadium — vanadium distances associated with this transition is similar to the Mott transition observed in the ${\mathrm{Cr}}_2$ ${\mathrm{O}}_3$-${\mathrm{V}}_2$ ${\mathrm{O}}_3$ system in which the conduction electrons localize on their ionic sites when proceeding from the metal phase, $\alpha -{\mathrm{V}}_2{\mathrm{O}}_3$, to the insulating one, $\alpha -{\left({\mathrm{V}}_{0.962}{\mathrm{Cr}}_{0.038}\right)}_2{\mathrm{O}}_3$.