Surface structure and polarization of cubic and tetragonal BaTiO3: An ab initio study

Cubic and tetragonal surfaces of BaTiO3 are investigated using the density functional theory (DFT) within the new generalized gradient approximation of Wu and Cohen (GGA-WC) to the exchange and correlation functional. The cubic and tetragonal surfaces of BaTiO3 are compared. For the tetragonal phase, we take into account two surface orientations (0 0 1) and (1 0 0) noted Tz and Tx, respectively. The atomic rumpling and the difference between interlayer distances are determined and compared to the experimental results as well as to previous theoretical ones. Atomic displacements are also highlighted by comparing the variation of c/a ratio along the selected surface slabs. Considerable tetragonality reduction is found for (0 0 1) surface termination of the tetragonal structure. This represents an important atomic redistribution compared to the other surfaces. Therefore, an important release of surface stress is noted for Tz termination. Stress is released for all BaO terminations in comparison with TiO2 terminations. Anisotropy of stress is noted for Tx terminations. The perpendicular polarization to the surface is cancelled due to electrostatic conditions of supercell construction. A parallel polarization is retained for BaO termination and not for TiO2 termination of Tx surface. Our findings are in good agreement with recent experimental ones.