First principles study of polarization-strain coupling in SrBi2Ta2O9

Paraelectric and ferroelectric phase structures of SrBi2Ta2O9 were calculated using first-principles density functional theory. Berry phase method is used to study the spontaneous polarization in ferroelectric SrBi2Ta2O9. The spontaneous polarizations of SrBi2Ta2O9 experimental and relaxed structures were calculated to be 34.1 μC/cm2 and 21.0 μC/cm2, respectively, along the crystallographic a-axis. It is found that the spontaneous polarization can be improved by both of ab- and bc-biaxial tensile strains. And the polarization value shows a sizable enhancement by 45% when applying 2.4% ab-biaxial tensile strain. The strain effects on spontaneous polarization are explained in terms of the atomic off-centre displacements.