First-principles study of ferroelectric and piezoelectric properties of tetragonal SrTiO3 and BaTiO3 with in-plane compressive structures

Ferroelectric and piezoelectric properties of tetragonal SrTiO3 and BaTiO3 with in-plane compressive structures have been investigated using a first-principles calculation. It has been found that the ferroelectric structure appears even in SrTiO3 with in-plane compressive structures. The piezoelectric constant e33e33 drastically increases in SrTiO3 rather than that in BaTiO3 as the tetragonal ratio c/ac/a (>1) is close to 1. On the other hand, e31e31 shows negative in SrTiO3 while positive in BaTiO3, although the changes in their absolute values are very small. We have found that these properties of e33e33 and e31e31 in SrTiO3 and BaTiO3 are closely related to the ionic distances.