First-Principles Study of Atomic Structure and Subsurface Dipoles of PbTiO3 (001) Surfaces

First-principles pseudopotential calculations were carried out to investigate the (001) surfaces of tetragonal and cubic PbTiO3. Both PbO- and TiO2-terminated surfaces were considered in a half-frozen-symmetrical model. The calculated results show that the surfaces of tetragonal and cubic PbTiO3 were different in many aspects because of the tetragonal ferroelectric distortion suppressing the surface relaxation. The net subsurface dipoles of tetragonal PbTiO3 slabs moved outward bulk. In comparison, that of cubic PbTiO3 slabs moved inward bulk. Nevertheless, there was no strong surface-induced polarization found in all investigated surface structures. The analysis of the structural stability indicates that the PbO-terminated (001) surface of cubic PbTiO3 was most energetically stable of the four considered surfaces, and the cubic PbTiO3 slabs were generally more stable than the tetragonal PbTiO3 ones. Moreover, the different terminated surfaces of tetragonal PbTiO3 have a comparable stability, while PbO-terminated surface of cubic PbTiO3 was much more energetically favorable.