Effect of doping and temperature on the crystal structure of (V 1− xMo x) 2O 3 above and below the metal/insulator transition

Abstract

The crystal structure of new molybdenum-doped vanadium sesquioxides (V 1− x Mo x ) 2O 3 (0⩽ x⩽0.20) has been studied at low temperature (10 K) and up to room temperature, through neutron and X-ray powder diffraction. The transition from insulating I- to metallic M-type phases, either by doping or thermally driven, is accompanied by an abrupt decrease of all interatomic distances. Within each structural type however, at 10 K, the effect of doping is essentially the same as at room temperature: it increases cation–oxygen distances, and decreases cation–cation distances, making the cationic coordination octahedra more regular. Thermal effects differ for each phase type: all interatomic distances normally increase in the M-type phase (but with different octahedral modifications depending on doping), but they decrease or remain constant in the I-type phase. This produces an unusual negative thermal expansion coefficient up to 5% at low temperature for the doped compounds.