Switchable Dielectric Phase Transition with Drastic Symmetry Breaking in a Sn(IV)-Based Perovskite-Type Halide Semiconductor

A new tin­(IV)-based perovskite-type hybrid semiconductor, bis­(trimethyl­iodomethyl­ammonium) hexachlorido­stannate­(IV) ([TMIM]2SnCl6), has been synthesized as a switchable dielectric phase transition material, featuring a zero-dimensional inorganic architecture of [SnCl6]2– octahedra and organic [TMIM]+ cations. It is found that [TMIM]2SnCl6 displays a reversible structural phase transition at 329 K, demonstrated by the differential scanning calorimetry (DSC) measurements. The dielectric constant exhibits remarkable steplike anomaly around the phase transition temperature (Tc), indicating switchable dielectric behaviors. Variable-temperature structure analyses disclose that the drastic symmetry breaking occurs with the structure transferring from Fm3̅m to C2/c by the temperature decreasing. The mechanism of such a transition is associated with the order–disorder transformation of organic ammonium and the displacement of the inorganic framework, which benefits from the discrete anionic architectures that provide enough space. Meanwhile, [TMIM]2SnCl6 shows a semiconducting property with a wide optical bandgap of ∼4.83 eV. This finding of the Sn­(IV)-based metal halide with prominent phase transition and semiconducting behaviors will direct an executable pathway for designing novel multifunctional perovskite-type switchable materials.