Metal-insulator transition and local structure of V₂O₃

According to diffraction measurements of the average structure, V₂O₃ changes on heating from monoclinic to trigonal, accompanied by a 1.4% volume decrease, where some V - V distances decrease by about 0.11 Å, favoring the Mott - Hubbard mechanism of the phase transition from insulator to metal. Our polarized XAFS measurements of the local structure of the single crystal V₂O₃ show the same decrease in volume but no change in local symmetry in the transition, indicating that the phase transition contains a significant order - disorder component, contrary to the purely displacive model based on diffraction results. XANES measurements found that the onset of the 1s → "3d" transition in the insulator shifts towards lower energies by about 1eV in the metal, consistent with the shielding of the core hole potential by conducting electrons.