Anomalous Enhancement of the p-d Hybridization in the a-bonds of ABO3 Perovskites Under the Lattice Expansion

摘要

The first-principle calculations of the electric field gradient (EFG) on oxygen site for SrTiO_3 and BaTiO_3 as a function of cubic lattice parameter a show the increase of the absolute value of the EFG under the lattice expansion due to the decrease of the population of a -orbitals. It means that the p-d hybridization in the σ -bonds increases with the increase of the bond length. We show that the non-trivial behavior is explained by the contribution of deep oxygen 2s states into the crystal field on Ti site.