Crystal Structure of the Low-Temperature Antiferromagnetic Phase of V2O3

At ~ 155 °K, the metallic corundum structure of V₂O₃ 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 Cr₂O₃-V₂O₃ system in which the conduction electrons localize on their ionic sites when proceeding from the metal phase, α-V₂O₃, to the insulating one, α-(V_0.962Cr_0.038)₂O₃.