Ab initio DFT study on ferroelectricity on perovskite surfaces and in thin-film capacitors

Ab initio DFT calculations based on the local density approximation were performed to study (a) in-plane polarized ferroelectricity (FE) at PbTiO3 (001) surfaces and (b) thin Pt/PbTiO3/Pt capacitors with perpendicular FE, and their relation with the lateral lattice parameter. A significant influence of lattice parameter on ferroelectricity was found in both cases. At PbTiO3 (001) surfaces, the in-plane FE in [110] direction is stable in both TiO2 and PbO terminations, and it is enhanced by a larger lattice parameter. Antiferrodistortive (AFD) rotation emerging at the PbO-terminated surface is suppressed by a lattice expansion by the competition with FE. Perpendicular FE polarization in Pt/PbTiO3/Pt films is suppressed by a lattice expansion. The critical thickness for ferroelectricity, who se stability is different for TiO2 and PbO terminations of PbTiO3, is obtained as a function of the lateral lattice parameter.