Metal-insulator transition in (V1-xCrx)(2)O-3

A first-order metal-insulator transition with no change in long-range order occurs in the mixed oxides (V1-xCrx)(2)O-3 with increasing x (x approximate to 0.01 at 1 atm and 298 degrees K) or decreasing pressure (at approximate to 10 kbar for x = 0.04 at 298 degrees K). In a preliminary letter it was shown that the transition had all the qualitative features expected of a Mott transition, i.e., a transition from band to localized behavior. The present paper reports the detailed experimental results. Single crystals of mixed oxides have been made by reaction of Cr2O3, V2O5, and VN in molten KF. Electrical resistivity and powder x-ray diffraction measurements made as a function of temperature and pressure in oxides with 0 <= x <= 0.12 establish a temperature-pressure-composition phase diagram with three clearly defined phases: metal (M), insulator (I), and antiferromagnetic insulator (AF). The I-M transition is marked by a drop of over two orders of magnitude in the electrical resistivity and a discontinuous decrease in volume of approximate to 1.2% with no change in crystal structure. For x approximate to 0.01 the sequence AF -> M -> I is observed with increasing temperature at 1 atm. At 4.2 K an AF -> M transition occurs with increasing pressure (P = 41 +/- 6 kbar for x = 0.04). The phase diagram is compared with other transition-metal oxides, and the differences between the transition in V2O3 and VO2 are discussed.