A metastable perovskite BiFe 0.5 Sc 0.5 O 3 synthesized under high-pressure (6 GPa) and high-temperature (1500 K) conditions was obtained in two different polymorphs, antipolar P nma and polar I ma2, through an irreversible behavior under a heating/cooling thermal cycling. The I ma2 phase represents an original type of a canted ferroelectric structure where Bi 3+ cations exhibit both polar and antipolar displacements along the orthogonal [110] p and [110] p pseudocubic directions, respectively, and are combined with antiphase octahedral tilting about the polar axis. Both the P nma and the I ma2 structural modifications exhibit a long-range antiferromagnetic ordering with a weak ferromagnetic component below T N ∼ 220 K. Analysis of the coupling between the dipole, magnetic, and elastic order parameters based on a general phenomenological approach revealed that the weak ferromagnetism in both phases is mainly caused by the presence of the antiphase octahedral tilting whose axial nature directly represents the relevant part of Dzyaloshinskii vector. The magnetoelectric contribution to the spontaneous magnetization allowed in the polar I ma2 phase is described by a fifth-degree free-energy invariant and is expected to be small.

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The high-pressure stabilised BiFe1−yScyO3 perovskites exhibit annealing-stimulated irreversible phase transitions, which allows them to be obtained in different structural polymorphs.