Large birefringence switching in a new zero-dimensional cyanide perovskite ferroelastic material

Abstract

Cyanide perovskites have demonstrated significant potential in the design of molecular ferroelastic, ferroelectric, and multiferroic materials. However, previous research has primarily focused on three-dimensional (3D) cyanide perovskites, which are structurally constrained and exhibit limited diversity. In this study, we synthesized a new zero-dimensional (0D) cyanide perovskite ferroelastic material, (MA)₃[Fe(CN)₆] (MA = CH₃NH₃, methylamine), and conducted comprehensive characterization through differential scanning calorimetry (DSC), dielectric measurements, variable-temperature structural analysis, and polarized light microscopy. (MA)₃[Fe(CN)₆] undergoes an isomorphic phase transition with a spontaneous strain of 0.1063. The birefringence at 300 K and 330 K is 0.302@546 nm and 0.022@546 nm, respectively. The substantial birefringence change up to 0.28 mainly originates from the rotational motion of inorganic and organic components. This work establishes a new pathway for designing 0D cyanide perovskite materials.