Low-Dimensional Noncollinear Ferroelectricity in Group-VI Oxyhalides*

Recently, interest in low-dimensional ferroelectric materials has grown rapidly across multiple scientific and engineering disciplines. Here, a serial group-VI oxyhalides MO_3-nX_2n is studied based on density functional theory calculations. For n=1, the dioxydihalides display quasi 2D properties with weak vdW interaction between layers. Each layer is predicted to present noncollinear ferrielectricity, induced by competing ferroelectric and antiferroelectric softmodes [1]. This intrinsic noncollinearity of dipoles generates unique physical properties, such as Z₂×Z₂ topological domains and atomic-scale dipole vortices [1]. For n=2, the dioxytetrahalides display quasi 1D characteristics. The robust ferroelectric distortion within each chain and weak vdW coupling between chains make them candidates for applications as high-density non-volatile memories [2]. Our investigations should open the door to a new branch of low-dimensional materials in the pursuit of intrinsically strong noncollinear ferrielectricity and high-performance functional materials.

[1] L.-F. Lin, et al., Phys. Rev. Lett. 123, 067601 (2019).
[2] L.-F. Lin, et al., Phys. Rev. Materials. 3, 111401(R) (2019).