Strain‐Driven Stabilization of a Room‐Temperature Chiral Multiferroic with Coupled Ferroaxial and Ferroelectric Order

Abstract Noncollinear ferroic materials are sought after as testbeds to explore the intimate connections between topology and symmetry, which result in electronic, optical, and magnetic functionalities not observed in collinear ferroic materials. For example, ferroaxial materials have rotational structural distortions that break mirror symmetry and induce chirality. When ferroaxial order is coupled with ferroelectricity arising from a broken inversion symmetry, it offers the prospect of electric‐field‐control of the ferroaxial distortions and opens up new tunable functionalities. However, chiral multiferroics, especially ones stable at room temperature, are rare. A strain‐stabilized, room‐temperature chiral multiferroic phase in single crystals of BaTiS 3 is reported here. Using first‐principles calculations, the stabilization of this multiferroic phase having P 6 3 space group for biaxial tensile strains exceeding 1.5% applied on the basal ab ‐plane of the room temperature P 6 3 cm phase of BaTiS 3 is predicted. The chiral multiferroic phase is characterized by rotational distortions of TiS 6 octahedra around the long c ‐axis and polar displacement of Ti atoms along the c ‐axis. The ferroaxial and ferroelectric distortions and their domains in P 6 3 ‐BaTiS 3 are directly resolved using atomic resolution scanning transmission electron microscopy. Landau‐based phenomenological modeling predicts a strong coupling between the ferroelectric and the ferroaxial order making P 6 3 ‐BaTiS 3 an attractive test bed for achieving electric‐field‐control of chirality.