Comparative structural and electrical studies of V2O3 and V2-xNixO3 (0<x<0.75) solid solution

V2O3 room and low temperature structures have been refined using PXRD and Rietveld procedures. At 15 K, in addition to the umbrella like opening of V-O bonds associated to the typical large V-V distance through the face shared octahedra (V-V-fsh) we have observed three different V-V distances through the edge shared octahedra (V-V-edsh) : 2.985 Angstrom, 2.908 Angstrom, and 2.847 Angstrom. This splitting is a consequence of the rotation of V-V pairs in a plane itself rotated out of the (ac) one which appears to be the origin for the well-known rhombohedral to monoclinic distortion. Ni for V substitutions drive to a V2-xNixO3 solid solution with a wide homogeneity range (0 < x < 0.75). Structure refinements on selected compositions show that at both room and 15 K temperatures the typical V2O3 corundum type is kept. At 300 K, the main Ni effect is a drastic decrease of the c parameter associated to a flattening of the octahedra but also to an increase of the M-M-fsh distance without rotation of the M-M pairs. This explains the absence of the monoclinic transition in the whole homogeneity and temperature ranges and shows clearly that a large M-M-fsh distance is not necessarily associated with the monoclinic form. Despite this large distance observed in the whole temperature range, the electric behavior exhibits a conductor to insulator transition. It is explained in terms of semi conduction via an electron hopping process between V3+ and V4+ cations which depends on Ni amounts. This last result implies also that a large M-M-fsh distance is not associated with an insulating behavior.