Hybrid functional study on the ferroelectricity of domain walls with O-vacancies in PbTiO3

Abstract

Nonlinear defect interactions between the 180° domain wall and oxygen-vacancies (O-vacancies) in PbTiO3, and the characteristic ferroelectricity due to the interactions are investigated using first-principles calculations based on the hybrid Hartree-Fock (HF) density functionals, which correctly reproduce the band gap and provide the accurate defect electronic structures. We show that an oxygen vacancy is likely to form at 180° domain walls than inside the bulk and the vacancy behaves as a double shallow donor that contributes to partial conductivity preferentially than that inside the bulk. The defect interactions between 180° domain walls and oxygen vacancies have a significant influence on the polarization distribution in PbTiO3, and the effect differs depending on the location of O-vacancies with respect to the domain wall. An oxygen vacancy that is located in the polar [001] direction relative to the Ti atom suppresses ferroelectricity around the vacancy in front of a domain wall, and enhances ferroelectricity only an the center of domain wall, which leads to a shift of the domain wall towards the vacancy and pinning of the domain wall. On the other hand, an O-vacancy that is located in the non-polar [100] and [010] directions relative to the Ti atom induces polarization perpendicular to the [010] axis and outward from the vacancy. Furthermore, the magnitude of polarization change around the O-vacancy inside the 180° domain wall is larger than inside the bulk, which originates from the strong interaction between the 180° domain wall and O-vacancy. These results will provide significant fundamental insight for the design of ferroelectrics.

Keywords

• ferroelectricity oxygen-vacancy
• domain wall
• perovskite type oxide
• density functional calculation