Ab initio calculations of the geometry and electronic structure of point defects in ferroelectrics with a perovskite structure

• Published in: Physics of the solid state Vol. 51; no. 5; pp. 982 - 990
• Main Author: Kvyatkovskiĭ, O. E.
• Format: Journal Article
• Language: English
• Published: Dordrecht SP MAIK Nauka/Interperiodica 01.05.2009
• Subjects: Magnetism and Ferroelectricity; Physics; Physics and Astronomy; Solid State Physics; 71.55.-i; 77.84.Dy; 61.72.S; 61.72.Bb
• ISSN: 1063-7834; 1090-6460
• DOI: 10.1134/S1063783409050163

Ab initio calculations of the optimized geometry and the electronic structure of lattice defects in incipient perovskite ferroelectrics SrTiO 3 and KTaO 3 are performed in the framework of the density functional theory. The results are presented for the Li + impurity ion at the A site in the KTaO 3 and SrTiO 3 ferroelectrics; the Mn 2+ , Cd 2+ , Ca 2+ , Mg 2+ , and Zn 2+ ions at the A site and the Mn 4+ and Mg 2+ ions at the B site in the SrTiO 3 compound; and the MN Ti 2+ - V O and Mg Ti 2+ - V O complexes in the SrTiO 3 ferroelectric. The results are obtained by the cluster method with allowance made for the structural relaxation initiated by the defect and, for nonisovalent substitutional impurities, with due regard for the charge and spin states of the defect. It is established that the Ca Sr 2+ , Cd Sr 2+ , Mn Ti 4+ , and Mg Ti 2+ ions have a stable central position, whereas the Li K + ion in the KTaO 3 compound and the Li Sr + , Mn Sr 2+ , and Zn Sr 2+ defects in the SrTiO 3 ferroelectric are off-center ions. The shape of the multiminimum adiabatic potential and the parameters of dielectric relaxators (activation barrier, dipole moment) for polar defects are obtained. The electronic impurity levels are determined for the Li Sr + and Mg Ti 2+ neutral defects.