Molecular design of high-temperature organic dielectric switches.

A design strategy of reducing the molecular symmetry was used to obtain a series of picrate-based high-temperature phase transition compounds. Their dielectric switching behaviours accompanied by phase transitions can be attributed to the order-disorder transitions of the cations and the displacements of both cations and anions.

Halogen substitution effects on optical and electrical properties in 3D molecular perovskites.

Both 3D organic-inorganic perovskites ([Et3P(CH2)2Cl][Cd(dca)3] (1) and [Et3P(CH2)2F][Cd(dca)3] (2) [dca = dicyanamide, N(CN)2-]) display two sequentially reversible high-temperature phase transitions and switchable dielectric properties. Through halogen substitution, 1 shows exceptional switching behaviour of second harmonic generation effects and remarkably 2 represents the first above-room-temperature 3D ferroelastic material characterized by two ferroelastic phases.

Photoluminescent-dielectric duple switch in a perovskite-type high-temperature phase transition compound: [(CH3)3PCH2OCH3][PbBr3].

A bistable optical-electrical duple switch belongs to a class of highly satisfying intelligent materials that can transform optical and electrical responses simultaneously in one device. A perovskite-type high-temperature phase transition compound with one-dimensional chain-like crystal structure, ([(CH3)3PCH2OCH3][PbBr3], 1), displays remarkable bistable photoluminescent-dielectric duple switching behaviors. The noteworthy order-disorder transition of the phosphonium cation and the motions of anions contribute to the phase transition, leading to the space group P21/c at a low temperature phase to C2/c at a high temperature phase. 1 exhibits a prominent step-like dielectric anomaly at 401.0 K and demonstrates novel optical properties with a band gap of 3.54 eV. The photoluminescence intensity suddenly declines from 398 K to 408 K, which may be attributed to the occurrence of phase transition. The electron cloud distributions of the frontier orbital in compound 1 have been calculated using a DFT program.

[(CH3)3PCH2OH][CdBr3] is a perovskite-type ferroelastic compound above room temperature.

A new organic-inorganic perovskite-type compound [(CH3)3PCH2OH][CdBr3] exhibits a ferroelastic phase transition at 339 K. Domain structures were observed and analyzed. The origin of the phase transition can be attributed to the motion or reorientation of the [(CH3)3PCH2OH]+ cations and the displacement of Cd2+ and Br- ions in solid-state crystals.