Crystal structure of the low-temperature antiferromagnetic phase of V2O3

At similar to 155 degrees K, the metallic corundum structureoOf 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 angstrom, while the vanadium - vanadium distance across the shared octahedral edge increases from 2.882 to 2.987 angstrom 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, alpha-V2O3, to the insulating one, alpha -(V0.962Cr0.038)(2)O-3.