Epitaxial strain induced ferroelectricity in rocksalt binary compound: Hybrid functional Ab initio calculation and soft mode group theory analysis

We have studied the detailed mechanism of epitaxial strain induced ferroelectricity in rocksalt binary compound by ab initio calculation and soft mode group theory analysis. By applying compressive strain, cubic binary rocksalt (F_m3m) transforms into tetragonal (I_4/mmm) structure. With increasing compressive strain, tetragonal structure becomes unstable against spontaneous transformation to lower symmetry tetragonal structure (I_4/mm), evident both from ab initio calculation and from soft mode group theory analysis. For the tensile strain, phase transition sequence can be cubic binary rocksalt to tetragonal (I_4/mmm) and to orthorhombic structure (I_m2m). From ab initio calculation and space group analysis, we propose that the epitaxial strain induced ferroelectricity of rocksalt binary compound is the generic property.