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.