Polarization of strained BaTiO3∕SrTiO3 artificial superlattice: First-principles study

We performed first-principles calculation to investigate the effect of epitaxial strain on lattice instabilities and polarization behavior of BaTiO3∕SrTiO3 artificial lattice with very short stacking period, i.e., BaTiO31unitcell∕SrTiO31unitcell(BTO∕STO). The structural analysis of BTO∕STO artificial superlattice under in-plane compressive state showed enhanced stability of the tetragonal phase. On the other hand, the stability of monoclinic phase was enhanced when the BTO∕STO was in the in-plane tensile state. The phase transition from tetragonal to the monoclinic phase occurs at the misfit strain of −0.25%. As the misfit strain of BTO∕STO superlattice increases from −0.25%to−1.5% (in-plane compressive state), the tetragonal superlattice exhibits an increasing polarization along the [001] direction. In the monoclinic phase, the polarization of the superlattice rotates progressively toward [110] direction with increasing the misfit strain, and the magnitude of the polarization simultaneously increases with the rotation. The first-principles study shows that the phase stability and polarization vector is sensitively influenced by the lattice misfit strain.