Orbital disordering and the metal-insulator transition with hole doping in perovskite-type vanadium oxides

Filling-control metal-insulator transitions (MITs) and related electronic phase diagrams have been investigated for hole-doped vanadium oxides Pr_1-xCaₓVO₃, Nd_1-xSrₓVO₃, and Y_1-xCaₓVO₃ with perovskite structure. The increase of the doping level x causes the melting of the G-type (and C-type) orbital order, prior to or concomitantly with the MIT, due partly to the doped-hole motion and partly to the random potential arising from the quenched disorder. In particular, the G-type spin- and C-type orbital-ordered phase present in Y_1-xCaₓVO₃ disappears immediately upon hole doping, around $x=0.02$. On the other hand, the critical doping level x for the MIT is governed by the electron-correlation strength of the undoped parent compound.