Metal-Insulator Transitions in Pure and DopedV2O3

The addition of ${\mathrm{Ti}}^{3+}$ and ${\mathrm{Mg}}^{2+}$ to ${\mathrm{V}}_2$ ${\mathrm{O}}_3$ leads to the suppression of the antiferromagnetic insulating phase; whereas the addition of ${\mathrm{Ti}}^{4+}$, ${\mathrm{Zr}}^{4+}$, and ${\mathrm{Fe}}^{3+}$ results in a first-order transition from a metallic to an insulating state. The effect of impurity ions is discussed in terms of the changes they cause in the bandwidth in analogy with the effect of pressure. The Hall coefficient of metallic ${\mathrm{V}}_2$ ${\mathrm{O}}_3$ at 4.2 °K and 20 kbar is $R_H=+(3.5\mathrm{}\pm 0.4)\times {10}^{-4\mathrm{}}$ ${\mathrm{cm}}^3$/C which is close to the value measured at 150 °K and 1 atm. The residual resistivity of metallic ${\mathrm{V}}_2$ ${\mathrm{O}}_3$ is strongly impurity dependent (140 μΩ cm/at.% Cr and 35 μΩ cm/at.% Ti). These results are not completely consistent with current theories for the metal-insulator transition in ${\mathrm{V}}_2$ ${\mathrm{O}}_3$ but the best available model still seems to involve a localized-to-nonlocalized transition within the $d$ band primarily involving orbitals in the basal plane.