One-dimensional cadmium thiocyanate perovskite ferroelastics tuned by halogen substitution

The organic-inorganic hybrid molecular ferroelastics have gained widespread attentions as a promising candidate for data storage, sensors and mechanical switches applications. However, it remains a great challenge to construct new molecular ferroelastic materials. Based on the ''quasi-spherical theory'', we designed and synthesized a new quasi-spherical cation [DMIE]+ ([DMIE]+ is dimethyl-isopropyl-ethyl-ammonium cation) to expect ferroelastic materials. Unfortunately, [DMIE][Cd(SCN)3] (1) undergoes a structural phase transition from space group P63 to P63/mmc, which is not among the 94 species of ferroelastic phase transitions as suggested by Aizu. Herein, by introducing electronegative halogen (F, Cl or Br) atoms to the [DMIE]+ cation, the symmetry groups of the corresponding cadmium thiocyanate perovskite get efficiently lowered to orthorhombic Pbca to induce ferroelastic phase transitions with an Aizu notation of 6/mmmFmmm. The spontaneous strain value reduces from 0.0778 in fluorinated product to 0.0...