LiNbO₃-Type InFeO₃: Room-Temperature Polar Magnet without Second-Order Jahn–Teller Active Ions

Great effort has been devoted to developing single-phase magnetoelectric multiferroics, but room-temperature coexistence of large electric polarization and magnetic ordering still remains elusive. Our recent finding shows that such polar magnets can be synthesized in small-tolerance-factor perovskites A FeO 3 with unusually small cations at the A -sites, which are regarded as having a LiNbO 3 -type structure (space group R 3 c ). Herein, we experimentally reinforce this finding by preparing a novel room-temperature polar magnet, LiNbO 3 -type InFeO 3 . This compound is obtained as a metastable quench product from an orthorhombic perovskite phase stabilized at 15 GPa and an elevated temperature. The structure analyses reveal that the polar structure is characterized by displacements of In 3+ ( d 10 ) and Fe 3+ ( d 5 ) ions along the hexagonal c -axis (pseudocubic [111] axis) from their centrosymmetric positions, in contrast to well-known perovskite ferroelectrics (e.g., BaTiO 3, PbTiO 3, and BiFeO 3 ) where d 0 transition-metal ions and/or 6 s 2 lone-pair cations undergo polar displacements through the so-called second-order Jahn–Teller (SOJT) distortions. Using density functional theory calculations, the electric polarization of LiNbO 3 -type InFeO 3 is estimated to be 96 μC/cm 2 along the c -axis, comparable to that of an isostructural and SOJT-active perovskite ferroelectric, BiFeO 3 (90–100 μC/cm 2 ). Magnetic studies demonstrate weak ferromagnetic behavior at room temperature, as a result of the canted G-type antiferromagnetic ordering of Fe 3+ moments below T N ∼ 545 K. The present work shows the functional versatility of small-tolerance-factor perovskites and provides a useful guide for the synthesis and design of room-temperature polar magnets.