Ab initio density functional theory study of strain effects on ferroelectricity at PbTiO3 surfaces

The PbTiO3 (001) surface structure with ferroelectric (FE) polarization parallel to the surface and its response to tangential strain have been studied using ab initio density functional theory calculations with the local density approximation. We find [110]-oriented ferroelectricity is more stable than [100]-oriented under zero and nonzero strain in both TiO2 and PbO terminations. Tensile strain enhances the FE distortion and suppresses the antiferrodistortive rotation, while the opposite trend is found under compression. The FE polarization direction alters with respect to the variation of the uniaxial strain owing to the preference of the polarization along the longer axis of rectangular lattices. The sensitivity of the FE rotation significantly differs depending on the layer at PbO-terminated c(2x2) surface, leading to the variation of polarization directions among the layers under uniaxial strain.