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Abstract

A first-order metal-insulator transition with no change in long-range order occurs in the mixed oxides ${({\mathrm{V}}_{1\ensuremath{-}x}{\mathrm{Cr}}_{x})}_{2}{\mathrm{O}}_{3}$ with increasing $x (x\ensuremath{\approx}0.01 \mathrm{at} 1 \mathrm{atm}\mathrm{and} 298 ^{\ensuremath{\circ}}\mathrm{K})$ or decreasing pressure (at $\ensuremath{\approx}10$ kbar for $x=0.04$ at 298 \ifmmode^\circ\else\textdegree\fi{}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 ${\mathrm{Cr}}_{2}$${\mathrm{O}}_{3}$, ${\mathrm{V}}_{2}$${\mathrm{O}}_{5}$, and VN in molten KF. Electrical resistivity and powder x-ray diffraction measurements made as a function of temperature and pressure in oxides with $0\ensuremath{\le}x\ensuremath{\le}0.12$ 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 $\ensuremath{\approx}1.2$% with no change in crystal structure. For $x\ensuremath{\approx}0.01$ the sequence AF\ensuremath{\rightarrow} M\ensuremath{\rightarrow} I is observed with increasing temperature at 1 atm. At 4.2 K an AF\ensuremath{\rightarrow} M transition occurs with increasing pressure ($P=41\ifmmode\pm\else\textpm\fi{}6$ kbar for $x=0.04$). The phase diagram is compared with other transition-metal oxides, and the differences between the transition in ${\mathrm{V}}_{2}$${\mathrm{O}}_{3}$ and V${\mathrm{O}}_{2}$ are discussed.

Metal-Insulator Transition in(V1−xCrx)2O3

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