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.
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