First-principles study of ferroelectric and piezoelectric properties of tetragonal SrTiO sub(3) and BaTiO sub(3) with in-plane compressive structures

Ferroelectric and piezoelectric properties of tetragonal SrTiO sub(3) and BaTiO sub(3) with in-plane compressive structures have been investigated using a first-principles calculation. It has been found that the ferroelectric structure appears even in SrTiO sub(3) with in-plane compressive structures. The piezoelectric constant e sub(33) drastically increases in SrTiO sub(3) rather than that in BaTiO sub(3) as the tetragonal ratio c/a (>1) is close to 1. On the other hand, e sub(31) shows negative in SrTiO sub(3) while positive in BaTiO sub(3), although the changes in their absolute values are very small. We have found that these properties of e sub(33) and e sub(31) in SrTiO sub(3) and BaTiO sub(3) are closely related to the ionic distances.