Defect and electronic structures of acceptor substituted lead titanate

The defects and electronic structures of the group IIIB (Al, Ga, In, and Tl) and group VB (Sb and Bi) element substituted lead titanates were studied using density functional theory calculations. All substitutes are found to favor immobile acceptor-oxygen-vacancy-acceptor defect clusters, which weaken the space charge effects by limiting the motions of oxygen vacancies. Furthermore, we found that the group IIIB and group VB substitutes take two distinct defect-cluster structures, respectively, along the z direction and in the xy plane, mainly due to the difference in the ionic size and the electronegativity. While the domain pinning enforced by the tail-to-tail polarization patterns along the z direction are relieved by the group IIIB substitutes, the group VB substitutes induce head-to-head polarization patterns in the xy plane, which make the domain pinning effects even weaker. (c) 2008 American Institute of Physics.