Ab Initio Study of the On-Site Potential for Divalent Impurities in Dilute Sr_1−xA_xTiO₃ Solid Solutions

Abstract

The off-center impurity model for divalent impurities in SrTiO₃ (Mn, Mg, Ca, Cd, Pb, Zn substituted for Sr) is checked. The results of ab initio Hartree-Fock and density functional theory (DFT) B3LYP cluster calculations of the local adiabatic potential for impurity atoms are presented. The results show that all impurity atoms, except Zn and Mg, move in single-well potentials, whereas Zn and Mg in Sr_1−x A _xTiO₃ are found to occupy off-center positions, as does the Li in K_1−xLi_xTaO₃, and move in the six-well local potential. It is found that Mn²⁺ion in a high spin state moves in a flat potential well. The strong effect of electron correlations on the local potentials for Zn and Mg is revealed.

Keywords:

• Ferroelectricity
• dielectric properties
• impurity
• local potential
• ab initio calculations
• SrTiO₃
• KTaO₃

PACS:

• 77.84
• 61.43

Acknowledgments

I am indebted to V.V. Lemanov and P.A. Markovin for numerous discussions of the work. This study was supported by the Russian Foundation for Basic Research (project No 03-02-17557) and by Program of the Branch of Physical Sciences of Russian Academy of Sciences.