Dresden 2009 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 31: Matter at Low Temperature: Materials

TT 31.2: Talk

Wednesday, March 25, 2009, 16:00–16:15, HSZ 304

Analysis of the electric field gradient in the perovskites SrTiO₃ and BaTiO₃: density functional and model calculations — •Katrin Koch¹, Roman Kuzian², Klaus Koepernik³, and Helge Rosner¹ — ¹Max-Planck-Institute for Chemical Physics of Solids, Dresden — ²Institute for Problems of Materials Science, Kiev — ³Leibniz Institute for Solid State and Materials Research, Dresden

We analyze recent measurements [1] of the electric field gradient on the oxygen site in the perovskites SrTiO₃ and BaTiO₃. We have performed density functional calculations within the local-orbital scheme FPLO using a recently implemented EFG module. The calculated values agree well with the experiment. We show that the electronic charge density around the oxygen ion is almost spherical for SrTiO₃ at the experimental volume, but surprisingly becomes more and more oblate with increasing lattice expansion. The same tendency in the density redistribution, that can be quantified as the increase of the difference in population of σ- and π- orbitals in the p shell, is found for BaTiO₃. Using a p-d like model Hamiltonian, we show that this counter-intuitive behavior can be explained by the contribution of oxygen 2s states to the crystal field on the Ti site. We argue that the surprisingly large difference between the observed electric field gradients of the two compounds in the cubic phase is mainly due to the difference in the on-site electronic density distribution. The proposed model description is of general relevance for all related transition metal oxides with similar crystal structure.

[1] R. Blinc et al. Condens. Matter 20, 085204 (2008)