First-Principles Study of Properties of Strained PbTiO_3/KTaO_3 Superlattice

The impacts of strain and polar discontinuities on the performance of superlattices have attracted widespread attention. Using first-principles calculation, we study the polarization and piezoelectricity of PbTiO_3/KTaO_3 (PTO/KTO) superlattices with strain and polar discontinuities. The strain caused by lattice mismatch between the superlattice and the substrate induces lattice distortion, the displacement of each atom and dynamical charge transfer between the Ti atom or Ta atom and the O atoms in the PTO/KTO superlattice. With more compressive or less tensile strain, the polarization value increases linearly, piezoelectric tensor e_31 (e_32) increases while e_33 and e_25 (e_16) increase negatively. Polarity discontinuity caused by the interfacial charge will produce large irreversible polarization. Proved by \it \Gamma-point phonons of PTO/KTO superlattices of different strain values, the polar discontinuity and the piezoelectric properties are just weakly dependent on temperature as found in PTO/KTO superlattices.