First-principles study on ferroelectricity atPbTiO3 surface steps

Abstract

We performed ab initio density functional theory calculations to investigate ferroelectricity atPbTiO3 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 toenhanced covalent Pb–O bonding because of the low coordination number of Pbatoms at the step edge. In contrast, ferroelectric distortions were suppressed atTiO2-terminations, because of electron transfer from Pb–O sites to Ti–O sites. Spontaneouspolarization at the surface step increased when tensile strain was applied in the [010] directionand decreased when compressive strain was applied. At a critical compressive strain, thepolarization direction changed and a polydomain structure was formed that consisted of90° and180° domain walls aligned with the surface step edge. This polydomain structurecompensates surface charges that would generate a depolarizing field, therebystabilizing ferroelectric distortions at the surface step. The polydomainstructure also explains the formation mechanism of the experimentally observed180° domain wall pinned at the surface step edge.