Dielectric Phase Transition of an A2BX4-Type Perovskite with a Pentahedral to Octahedron Transformation
Organic-inorganic hybrid compounds with reversible dielectric phase transitions are a very attractive class of smart materials for their wide applications in data storage, data communication and signal sensing. Here, the piperidine ring C5H11N was introduced into the inorganic lead halide perovskite scaffold to obtain three hybrid perovskite compounds, [C5H12N]2PbCl4 (1), [C5H12N]2PbBr4 (2), and [C5H12N]PbI3 (3). When compound 2 and compound 3 feature static two-dimensional (2D) and one-dimensional (1D) perovskite structures, respectively, it is striking that compound 1 exhibits a reversible pentahedral to octahedron transformation. It undergoes an above-room-temperature dielectric phase transition at Tc ≅ 352 K, wherein the high dielectric constant is more than twice of the low dielectric constant. Structural analysis shows that 1 undergoes a phase transition from the space group Pnma of the low temperature phase (LTP) to C2/c at the high temperature phase (HTP). The phase transition originates from the order-disorder conversion of piperidinium cations. It is interesting to note that, the Pb2+ cations in the inorganic moieties change from five-coordinate at LTP to six-coordinate at HTP. The discovery of dielectric phase transition hybrid organic-inorganic lead halide perovskite materials further advances the potential application of high temperature responsive dielectric switchable materials.