关键词: ferroelectricity, spontaneous polarization, polarization mismatch, internal electric field

Abstract: We have performed the first-principles calculation to investigate the origins of ferroelectricities and different polarization behaviours of superlattices BaTiO$_{3}$/SrTiO$_{3}$ and PbTiO$_{3}$/SrTiO$_{3}$. The density of state (DOS) and electronic charge profiles show that there are strong hybridizations between atoms Ti and O and between atoms Pb and O which play very important roles in producing the ferroelectricities of superlattices BaTiO$_{3}$/SrTiO$_{3}$ and PbTiO$_{3}$/SrTiO$_{3}$. Owing to the decline of internal electric field in SrTiO$_{3}$ (ST) layer, the tetragonality and polarizations of superlattices decrease with increasing the fraction of SrTiO$_{3}$ in the superlattices. We find that the polarization of PbTiO$_{3}$/SrTiO$_{3}$ is larger$_{ }$than that of BaTiO$_{3}$/SrTiO$_{3}$ at the same ratio of components, because the polarization mismatch between PbTiO$_{3}$ and SrTiO$_{3}$ is larger than that between BaTiO$_{3}$ and SrTiO$_{3}$. The polarization and tetragonality are enhanced with respect to those of bulk tetragonal BaTiO$_{3}$ in the superlattices BaTiO$_{3}$/SrTiO$_{3}$, while the polarization and tetragonality are reduced with respect to those of bulk tetragonal PbTiO$_{3}$ in superlattices PbTiO$_{3}$/SrTiO$_{3}$.

Key words: ferroelectricity, spontaneous polarization, polarization mismatch, internal electric field