Dielectric phase transition of an A2BX4-type perovskite with a pentahedral to octahedral transformation

Organic-inorganic hybrid compounds that undergo reversible dielectric phase transitions are a very attractive class of smart materials due to their wide applications in data storage, data communication and signal sensing. Here, a 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 shows a reversible pentahedral to octahedral transformation. It undergoes an above-room-temperature dielectric phase transition at T_c≅ 352 K, wherein the high dielectric constant is more than twice the low dielectric constant. Structural analysis shows that 1 undergoes a phase transition from the space group Pnma at 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 the LTP to six-coordinate at the HTP. The discovery of dielectric phase transition hybrid organic-inorganic lead halide perovskite materials further enhances the potential applications of high temperature responsive dielectric switchable materials.

Reversible high temperature dielectric switching in a 2H-perovskite compound: [Me3NCH2CH3]CdCl3

A new organic–inorganic 2H-perovskite compound shows a noteworthy switchable dielectric phase transition at high temperature.

Successive near-room-temperature dielectric phase transitions in a lead-free hybrid perovskite-like compound

We have reported a lead-free organic–inorganic hybrid compound, (hexamethyleneimine)₂BiBr₅ (1), which undergoes three successive phase transitions in the vicinity of room temperature.

Switchable Dielectric Phase Transition Triggered by Pendulum-Like Motion in an Ionic Co-crystal

Molecular-based ionic co-crystals, which have the merits of low-cost/easy fabrication processes and flexible structure and functionality, have already exhibited tremendous potential in molecular memory switches and other electric devices. However, dipole (ON/OFF switching) triggering is a huge challenge. Here, we introduce a pendulum-like dynamic strategy to induce the order-disorder transition of a co-crystal [C₅ H₇ N₃ Cl]₃ [Sb₂ Br₉ ] (compound 1). Here, the anion and cation act as a stator and a pendulum-like rotor (the source of the dielectric switch), respectively. The temperature-dependent dielectric and differential scanning calorimetry (DSC) analyses reveal that 1 undergoes a reversible phase transition, which stems from the order-disorder transition of the cations. The thermal ON/OFF switchable motions make 1 a promising candidate to promote the development of bulk crystals as artificial intelligent dielectric materials. In addition, the pendulum-like molecular dynamics and distinct arrangements of two coexisting ions with a notable offset effect promotes/hinders dipolar reorientation after dielectric transition and provides a rarely observed but fairly useful and feasible strategy for understanding and modulating the dipole motion in crystalline electrically polarizable materials.

[C6 H14 N]PbBr3 : An ABX3 -Type Semiconducting Perovskite Hybrid with Above-Room-Temperature Phase Transition

Organic-inorganic hybrid perovskites, with the formula ABX₃ (A=organic cation, B=metal cation, and X=halide; for example, CH₃ NH₃ PbI₃ ), have diverse and intriguing physical properties, such as semiconduction, phase transitions, and optical properties. Herein, a new ABX₃ -type semiconducting perovskite-like hybrid, (hexamethyleneimine)PbBr₃ (1), consisting of one-dimensional inorganic frameworks and cyclic organic cations, is reported. Notably, the inorganic moiety of 1 adopts a perovskite-like architecture and forms infinite columns composed of face-sharing PbBr₆ octahedra. Strikingly, the organic cation exhibits a highly flexible molecular configuration, which triggers an above-room-temperature phase transition, at T_c =338.8 K; this is confirmed by differential scanning calorimetry (DSC), specific heat capacity (C_p ), and dielectric measurements. Further structural analysis reveals that the phase transition originates from the molecular configurational distortion of the organic cations coupled with small-angle reorientation of the PbBr₆ octahedra inside the inorganic components. Moreover, temperature-dependent conductivity and UV/Vis absorption measurements reveal that 1 also displays semiconducting behavior below T_c . It is believed that this work will pave a potential way to design multifeatured perovskite hybrids by utilizing cyclic organic amines.

A high temperature reversible phase transition in a supramolecular complex of 15-crown-5 with tetraphenylboron sodium

High temperature (391 K) reversible phase transition and large thermal hysteresis (19 K) was observed in 15-crown-5 clathrates: [Na(15-crown-5)][BPh₄] (15-crown-5 = 1,4,7,10,13-pentaoxacyclopentadecane, NaBPh₄ = sodium tetraphenylboron).

Switchable dielectric phase transition originating from disorder–order transformation and distortion in {[(C4H4N2)Co(H2O)4]SO4·2H2O}n

Disorder–order transition of the SO₄²⁻ and distortion of the [(C₄H₄N₂)Co(H₂O)₄]²⁺ chain induce the phase transition of {[(C₄H₄N₂)Co(H₂O)₄]SO₄·2H₂O}_n.

N-Methylpyrrolidinium hydrogen tartrate (NMPHT): an above-room-temperature order–disorder molecular switchable dielectric material

A new above-room-temperature molecular switchable dielectric material, which undergoes a first-order phase transition induced by the order-disorder transformation of cation, has been reported.

A perovskite-type cage compound as a temperature-triggered dielectric switchable material

The perovskite-type cage compound [C₃H₆NH₂]₂[KCo^III(CN)₆] shows a temperature-triggered dielectric switch. The switchable properties are derived from an order–disorder phase transition of a system, by changing the motions of the polar azetidine cation guests.