Acceptor modulated defect and electronic structures in ferroelectric lead titanate: An AB initio study

Abstract

Defects and electronic structures of the aliovalent acceptors substituted lead titanates were studied using density functional theory calculations. Three types of defect structures are identified in 3d transition metal and the group IIB and VB elements substituted systems. Cr substitute and oxygen vacancies are found to be dissociated from each other, forming an isolated point defect structure. In contrast, all other substitutes favor the immobile acceptoroxygenvacancyacceptor defect clusters which weaken the space charge effects by limiting the motions of oxygen vacancies. Furthermore, two distinct defect-cluster structures (along the z direction and in the xy plane, respectively) are observed. We conclude that the defect structure in the xy plane induces head-to-head polarization patterns, which make the domain pinning effects even weaker. The electronic structures due to elements substitutions are also investigated and compared. © 2008 World Scientific Publishing Company.