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.