Note on a Phase Transition in VO2.

Abstract

The powder diffractogram of vanadium dioxide crystals was found to change, rapidly and reversibly, at about 70 deg C, the most obvious feature being the disappearance of all reflections hkl with h odd. At 180 deg C the effect was even greater and the crystal structure was derived and found to be essentially of the rutile type. A small splitting, less than the a/sub 1/ - a/sub 2/ separation, of the 101 and 210 powder reflections indicates a slight residual deformation of the rutile-type cell. The structural data obtained at 180 deg C are: space group, P4/sub 2//mnm (No. 136); unit cell dimensions, a = 4.530 plus or minus 0.009 A and c = 2.869 plus or minus 0.006 A; cell content, 2VO/sub 2/ ;, 2V in 2(a), 000, 1/2 1/2 1/2; 4 0 in 4(f), xxO etc., x = 0.305 plus or minus 0.003; and reliability factor R = 0.12. The transition is accompanied by changes in the expansion coefficient, the electrical resistivity, and the magnetic susceptibility. (N.W.R.)