Analysis of the electric field gradient in the perovskites SrTiO3 and BaTiO3 : Density functional and model calculations
Abstract
We analyze recent measurements [R. Blinc, V. V. Laguta, B. Zalar, M. Itoh, and H. Krakauer, J. Phys.: Condens. Matter 20, 085204 (2008)] of the electric field gradient on the oxygen site in the perovskites SrTiO3 and BaTiO3 , which revealed, in agreement with calculations, a large difference in the electric field gradient (EFG) for these two compounds. In order to analyze the origin of this difference, we have performed density functional electronic-structure calculations within the local-orbital scheme FPLO. Our analysis reveals the counter-intuitive behavior that the EFG increases upon lattice expansion. Application of the standard model for perovskites, the effective two-level p-d Hamiltonian, cannot explain the experimentally observed and theoretically predicted behavior. In order to describe the EFG dependence correctly, a model beyond the usually sufficient p-d Hamiltonian is needed. We demonstrate that the counter-intuitive increase in the EFG upon lattice expansion can be explained by an s-p-d model containing the contribution of the oxygen 2s states to the crystal field on the Ti site. The proposed model extension is of general relevance for all related transition-metal oxides with similar crystal structure.
- Publication:
-
Physical Review B
- Pub Date:
- September 2009
- DOI:
- 10.1103/PhysRevB.80.125113
- arXiv:
- arXiv:0903.4015
- Bibcode:
- 2009PhRvB..80l5113K
- Keywords:
-
- Condensed Matter - Materials Science
- E-Print:
- 10 pages, 4 figures