paper

Hybridization effects and bond-disproportionation in the bismuth perovskites

arXiv:1410.0945 · doi:10.1103/PhysRevB.91.121114

Abstract

We propose a microscopic description of the bond-disproportionated insulating state in the bismuth perovskites BiO (=Ba, Sr) that recognizes the bismuth-oxygen hybridization as a dominant energy scale. It is demonstrated using electronic structure methods that the breathing distortion is accompanied by spatial condensation of hole pairs into local, molecular-like orbitals of the symmetry composed of O- and Bi- atomic orbitals of collapsed BiO octahedra. Primary importance of oxygen -states is thus revealed, in contrast to a popular picture of a purely ionic Bi/Bi charge-disproportionation. Octahedra tilting is shown to enhance the breathing instability by means of a non-uniform band-narrowing. We argue that formation of localized states upon breathing distortion is, to a large extent, a property of the oxygen sublattice and expect similar hybridization effects in other perovskites involving formally high oxidation state cations.

5 pages, 4 figures

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