Theoretical study on two dimensional group IV-VI ternary compounds with large in-plane spontaneous polarization

•Janus 2D group IV-VI ternary ferroelectric compounds are theoretically designed.•The spontaneous polarization of these compounds can reach up to 5.03*10−10C/m.•The ferroelectric order of these compounds can be maintained at room temperature.•Their polarization can be effectively modulated by the external strain.