Intercalation-driven ferroelectric-to-ferroelastic conversion in a layered hybrid perovskite crystal

Two-dimensional (2D) organic-inorganic hybrid perovskites have attracted intense interests due to their quantum well structure and tunable excitonic properties. As an alternative to the well-studied divalent metal hybrid perovskite based on Pb 2+ , Sn 2+ and Cu 2+ , the trivalent metal-based (eg. Sb 3+ with ns2 outer-shell electronic configuration) hybrid perovskite with the A 3 M 2 X 9 formula (A = monovalent cations, M = trivalent metal, X = halide) offer intriguing possibilities for engineering ferroic properties. Here, we synthesized 2D ferroelectric hybrid perovskite (TMA) 3 Sb 2 Cl 9 with measurable in-plane and out-of-plane polarization. Interestingly, (TMA) 3 Sb 2 Cl 9 can be intercalated with FeCl 4 ions to form a ferroelastic and piezoelectric single crystal, (TMA) 4 -Fe(iii)Cl 4 -Sb 2 Cl 9 . Density functional theory calculations were carried out to investigate the unusual mechanism of ferroelectric-ferroelastic crossover in these crystals.