A metastable perovskite ${\text{BiFe}}_{0.5}$${\text{Sc}}_{0.5}$${\text{O}}_3$ synthesized under high-pressure (6 GPa) and high-temperature (1500 K) conditions was obtained in two different polymorphs, antipolar $Pnma$ and polar $Ima2$, through an irreversible behavior under a heating/cooling thermal cycling. The $Ima2$ phase represents an original type of a canted ferroelectric structure where Bi${}^{3+}$ cations exhibit both polar and antipolar displacements along the orthogonal ${\left[110\right]}_p$ and ${\left[1\overline{1}0\right]}_p$ pseudocubic directions, respectively, and are combined with antiphase octahedral tilting about the polar axis. Both the $Pnma$ and the $Ima2$ structural modifications exhibit a long-range antiferromagnetic ordering with a weak ferromagnetic component below $T_N\sim 220$ 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 $Ima2$ phase is described by a fifth-degree free-energy invariant and is expected to be small.

• Received 27 February 2014
• Revised 18 April 2014

DOI:https://doi.org/10.1103/PhysRevB.89.174414