Crystal Structure of Metastable Perovskite Bi(Mg_1/2Ti_1/2)O₃: Bi-Based Structural Analogue of Antiferroelectric PbZrO₃

A metastable perovskite phase of Bi(Mg 1/2 Ti 1/2 )O 3 composition (BMT) has been obtained under high-pressure (6 GPa) and high-temperature (1270 K) conditions. X-ray and electron diffraction studies have revealed a complex superstructure originating from antiferroelectric-like displacements of Bi 3+ cations and octahedral tilting. A group theoretical analysis was used to enumerate the possible crystal structures compatible with both types of the distortions. On the basis of the symmetry arguments in combination with the diffraction methods, it has been concluded that the perovskite BMT is characterized by the orthorhombic Pnnm space group with unit cell parameters a = 11.3207(10) Å, b = 5.6433(10) Å, and c = 7.8314(10) Å. A relation of the BMT crystal structure to that commonly accepted for antiferroelectric perovskite PbZrO 3 (PZ) is discussed.