Electrically driven octahedral rotations in SrTiO₃ and PbTiO₃

We investigate the oxygen octahedral rotations that occur in two perovskites, SrTiO₃ and PbTiO₃, as a function of applied three-dimensional electric displacement field, allowing us to map out the phase diagram of rotations in both the paraelectric and ferroelectric regions of the polar response. First-principles calculations at fixed electric displacement field are used to extract parameters of a Landau-Devonshire model that is analyzed to identify the phase boundaries between different rotational states. The calculations reveal a rich phase diagram of rotations versus applied field in both SrTiO₃ and PbTiO₃, although the details are quite different in the two cases.