How chemistry controls electron localization in 3d1 perovskites

Transition metal perovskites have been studied for decades because of their unusual electronic and magnetic properties arising from narrow 3d bands and strong Coulomb correlations. The 3d1 perovskites are particularly interesting since despite the lack of multiplet effects similar materials have very different electronic properties: strontium and calcium vanadate are correlated metals with mass-enhancements of respectively 2.7 and 3.6, while lanthanum and yttrium titanate are Mott insulators with gaps of respectively 0.2 and 1 eV. Associated with the increasing electron localization along this series is a structural GdFeO3type distortion (Fig. 1 top): Whereas SrVO3 is cubic, the corner-sharing BO3 octahedra of the other perovskites are tilted and rotated in such a way that there are 4 equivalent octahedra per primitive cell. The reason often given for the progression of this distortion is that the size of the A cation relatively to that of the BO3 octahedron shrinks along the series, i.e., that r(Sr2+)∼r(La3+)>r(Ca2+)∼r(Y3+), while r(V5+)<r(Ti3+).