The first-principles study of ferroelectric behaviours of PbTiO3/SrTiO3 and BaTiOn/SrTiO3 superlattices

We have performed the first-principles calculation to investigate the origins of ferroelectricities and different po- larization behaviours of superlattices BaTiO3/SrTiO3 and PbTiO3/SrTiO3. 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 BaTiO3/SrTiO3 and PbTiO3/SrTiO3. Ow- ing to the decline of internal electric field in SrTiO3 （ST） layer, the tetragonality and polarizations of superlattices decrease with increasing the fraction of SrTiO3 in the superlattices. We find that the polarization of PbTiO3/SrTiO3 is largerthan that of BaTiO3/SrTiO3 at the same ratio of components, because the polarization mismatch between PbTiO3 and SrTiO3 is larger than that between BaTiO3 and SrTiO3. The polarization and tetragonality are en- hanced with respect to those of bulk tetragonal BaTiO3 in the superlattices BaTiO3/SrTiO3, while the polarization and tetragonality are reduced with respect to those of bulk tetragonal PbTiO3 in superlattices PbTiO3/SrTiO3.

The first-principles study of ferroelectric behaviours of PbTiO3/SrTiO3 and BaTiO3/SrTiO3 superlattices

We have performed the first-principles calculation to investigate theorigins of ferroelectricities and different polarization behavioursof superlattices BaTiO$_{3}$/SrTiO$_{3}$ and PbTiO$_{3}$/SrTiO$_{3}$. Thedensity of state (DOS) and electronic charge profiles show that there arestrong hybridizations between atoms Ti and O and between atoms Pb and Owhich play very important roles in producing the ferroelectricities ofsuperlattices BaTiO$_{3}$/SrTiO$_{3}$ and PbTiO$_{3}$/SrTiO$_{3}$. Owing tothe decline of internal electric field in SrTiO$_{3}$ (ST) layer, thetetragonality and polarizations of superlattices decrease with increasingthe fraction of SrTiO$_{3}$ in the superlattices. We find that thepolarization of PbTiO$_{3}$/SrTiO$_{3}$ is larger$_{ }$than that ofBaTiO$_{3}$/SrTiO$_{3}$ at the same ratio of components, because thepolarization mismatch between PbTiO$_{3}$ and SrTiO$_{3}$ is larger thanthat between BaTiO$_{3}$ and SrTiO$_{3}$. The polarization and tetragonalityare enhanced with respect to those of bulk tetragonal BaTiO$_{3}$ in thesuperlattices BaTiO$_{3}$/SrTiO$_{3}$, while the polarization andtetragonality are reduced with respect to those of bulk tetragonalPbTiO$_{3}$ in superlattices PbTiO$_{3}$/SrTiO$_{3}$.