First-principles investigation of the highly tetragonal ferroelectric material Bi (Zn 1/2 Ti 1/2) O 3

First-principles calculations were performed to study the extremely tetragonal ferroelectric material Bi(Zn1/2Ti1/2)O3 (BZT). In agreement with experiment, we find that BZT displays extremely large cation displacements and tetragonality. Despite its high tetragonality and polarization, the local structure of the material exhibits a high degree of local disorder which is more typical of the solid solutions close to the morphotropic phase boundary. For the tetragonal phase of BZT, we show that a planar ordered (001) B-cation arrangement with the Zn and Ti stacking direction perpendicular to direction of P is the lowest in energy, in contrast with the (111) B-cation ordering usually found in perovskites. We attribute this unusual preference to the large cation displacements found in BZT, which raises the importance of A−B cation repulsive interactions, favoring separation of Zn and Ti cations.