Steric Effect Induced Modulation on Crystallographic Symmetry: Implementing Ferroelasticity in Molecular Ferroelectric

Ferroelastic materials, as a significant category within the primary ferroic materials, have paved the way for the development of shape memory, superelasticity, tunable electronics, MEMS and actuators. The ferroic phase transition rules summarized by Aizu provides a theoretical guideline for material design. However, ferroelectrics and ferroelastics are to some extent intertwined with each other. Decoupling these properties is essential for optimizing material performance and developing better theoretical models. By modifying [(CH3)4N][FeCl4], a typical molecular ferroelectric that is not ferroelastic, we synthesized (Me2EtNCH3CH2Cl)FeCl4 (DMCE-FeCl4), an organic–inorganic hybrid compound that introduces ferroelasticity while maintaining ferroelectricity. DFT calculations reveal that the shape of the organic cations contributes to ferroelasticity, while their dipole moments contribute to ferroelectricity. This work advances the understanding of ferroic properties and their independent control, with implications for reconfigurable memory devices and intelligent actuators.