title: First-principles study on ferroelectricity at PbTiO3 surface steps.
abstract: We performed ab initio density functional theory calculations to investigate ferroelectricity at PbTiO(3) surface steps consisting of (100) and (001) surfaces with the polar axis in the [010] direction. Ferroelectricity was enhanced at PbO-terminated surface steps due to enhanced covalent Pb-O bonding because of the low coordination number of Pb atoms at the step edge. In contrast, ferroelectric distortions were suppressed at TiO(2)-terminations, because of electron transfer from Pb-O sites to Ti-O sites. Spontaneous polarization at the surface step increased when tensile strain was applied in the [010] direction and decreased when compressive strain was applied. At a critical compressive strain, the polarization direction changed and a polydomain structure was formed that consisted of 90° and 180° domain walls aligned with the surface step edge. This polydomain structure compensates surface charges that would generate a depolarizing field, thereby stabilizing ferroelectric distortions at the surface step. The polydomain structure also explains the formation mechanism of the experimentally observed 180° domain wall pinned at the surface step edge.
authors.affiliation: Department of Mechanical Engineering and Science, Kyoto University, Yoshida-hommachi, Sakyo-ku, Kyoto 606-8501, Japan. shimada@cyber.kues.kyoto-u.ac.jp
authors.forename: T
authors.initials: T
authors.lastname: Shimada
authors.forename: S
authors.initials: S
authors.lastname: Tomoda
authors.forename: T
authors.initials: T
authors.lastname: Kitamura