METAL-INSULATOR-TRANSITION AND LOCAL-STRUCTURE OF V2O3

According to diffraction measurements of the average structure, V2O3 c hanges on heating from monoclinic to trigonal, accompanied by a 1.4% v olume decrease, where some V-V distances decrease by about O.11 Angstr om, favoring the Mott-Hubbard mechanism of the phase transition from i nsulator to metal. Our polarized XAFS measurements of the local struct ure 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 mea surements found that the onset of the 1s --> ''3d'' transition in the insulator shifts towards lower energies by about leV in the metal, con sistent with the shielding of the core hole potential by conducting el ectrons.