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

Above room-temperature dielectric switching and semiconducting properties of a layered organic-inorganic hybrid compound: (C6H12N)2Pb(NO3)4

The well-studied star compound, CH3NH3PbI3, has attracted plenty of attention because of its remarkable optical and electrical properties. Consequently, new switching multifunctional hybrid compounds can be widely used in many fields such as solar cells, light-emitting diodes, optical data storage and so on. Therefore, switching multifunctional hybrid compounds with dielectric and semiconducting properties simultaneously will also find roles in the next generation of optoelectronic coupling materials. In fact, discovering an effective method to synthesize (multi)functional hybrid materials remains a pressing challenge. Thanks to the "quasi-spherical theory" proposed by Xiong et al., we used 7-azabicyclo[2.2.1]heptane as the quasi-spherical cation to construct molecule-based crystalline materials that exhibit responsive properties. Then, we tried to exploit the knowledge of crystal engineering and coordination chemistry to explain (multi)functional molecular materials. A layered organic-inorganic hybrid compound, (C6H12N)2Pb(NO3)4 (1), was grown and its dielectric switching property and semiconducting behaviour were investigated. Insights from differential scanning calorimetry measurements, variable-temperature X-ray structural studies, and dielectric spectroscopy revealed the origin of the phase transition, which is related to the motion of the organic ammonium and inorganic framework in solid-state crystals. Furthermore, 1 is also a wide bandgap semiconductor with an optical bandgap of 3.53 eV. The realization of switching and semiconducting properties simultaneously in layered Pb-based perovskites has a great significance toward research into hybrid compounds and the development of dielectric-optoelectronic integrated materials.

Crystal structures and phase transitions of imidazolium hypodiphosphates

Two imidazolium hypodiphosphates, (C₃H₅N₂)(H₃P₂O₆) (I) and (C₃H₅N₂)₂(H₂P₂O₆) (II), have been synthesized and structurally characterized. In both metal-free organic-inorganic hybrids (I) and (II), the hypodiphosphate mono- and dianions, (H₃P₂O₆)^- and (H₂P₂O₆)^2-, form hydrogen-bonded frameworks of different types, to which the organic cations are linked via N-H...O and C-H...O hydrogen bonds. The purity of the compounds was confirmed by powder X-ray diffraction. Differential scanning calorimetry of compound (I) revealed two structural phase transitions: continuous at 311.8 K [cooling/heating; from high-temperature phase (HTP) to room-temperature phase (RTP)] and a discontinuous one at 287.9/289.2 K [RTP → low-temperature phase (LTP)]. Compound (I) is characterized in a wide temperature range by single-crystal and powder X-ray diffraction methods. Crystal structures of high- and low-temperature phases are determined, which show orthorhombic (HTP, Pnna, No. 52) → monoclinic (LTP, P2₁/n11, No. 14, a-axis doubled) structural change on cooling with an intermediate incommensurately modulated phase (RTP). Dynamic properties of polycrystalline (I) were studied by means of dielectric spectroscopy. The dielectric behaviour is explained by the motion of imidazolium cations.

Exploring a lead-free organic-inorganic semiconducting hybrid with above-room-temperature dielectric phase transition

Recently, organic-inorganic hybrid lead halide perovskites have attracted great attention for optoelectronic applications, such as light-emitting diodes, photovoltaics and optoelectronics. Meanwhile, the flexible organic components of these compounds give rise to a large variety of important functions, such as dielectric phase transitions. However, those containing Pb are harmful to the environment in vast quantities. Herein, a lead-free organic-inorganic hybrid, (C6H14N)2BiCl5 (CHA; C6H14N+ is cyclohexylaminium), has been successfully developed. As expected, CHA exhibits an above-room-temperature solid phase transition at 325 K (T c), which was confirmed by the differential scanning calorimetry measurement and variable temperature single crystal X-ray diffraction analyses. Further analyses indicate the phase transition is mainly governed by the order-disorder transformation of organic cyclohexylaminium cations. Interestingly, during the process of phase transition, the dielectric constant (ε') of CHA shows an obvious step-like anomaly, which displays a low dielectric constant state below T c and a high dielectric constant state above T c. Furthermore, variable temperature conductivity combined with theoretical calculations demonstrate the notable semiconducting feature of CHA. It is believed that our work will provide useful strategies for exploring lead-free organic-inorganic semiconducting hybrid materials with above room temperature dielectric phase transitions.

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.

[C6N2H18][SbI5]: A Lead-free Hybrid Halide Semiconductor with Exceptional Dielectric Relaxation

[C₆N₂H₁₈][SbI₅] (1), a novel metal halide semiconductor with dielectric relaxation behavior, has been successfully synthesized, in which the cavities between the one-dimensional [SbI₅] _n^2- polyanions are occupied by 2-methyl-1,5-pentanediammonium (2-MPDA) cations. 1 undergoes a reversible solid-state phase transition at T_C = 192.7 K and shows a step-like dielectric anomaly. Interestingly, above T_C, distinct dielectric dispersion in a wide temperature range is also witnessed. Remarkably, the solid state UV-vis diffuse reflectance spectrum of 1 exhibits a slightly gentler absorption edge at about 650 nm; that is, 1 adopts an indirect band gap with 1.92 electron volts. The combined narrow band gap, strong photoconductivity effect, and excellent dielectric relaxation might shed light on the exploitation of lead-free hybrid metal halide molecular materials with promising application prospects in thermoresponsive relaxation-type dielectric materials and photovoltaic conversion devices.

[C5 H12 N]SnCl3 : A Tin Halide Organic-Inorganic Hybrid as an Above-Room-Temperature Solid-State Nonlinear Optical Switch

Nonlinear optical (NLO) switches driven by a solid-state structural phase transition have attracted extensive attention; however, above-room-temperature solid-state NLO switch materials are still sparse. Herein, we report an above-room-temperature tin halide organic-inorganic hybrid quadratic NLO switchable material, N-methylpyrrolidinium trichloride stannite ([C₅ H₁₂ N]SnCl₃ , MPSC). The MPSC crystal exhibits a phase-matchable NLO property that is 1.1 times that of KH₂ PO₄ (KDP) and NLO switching behavior, changing from a high second harmonic generation (SHG) response to a low SHG response at 383 K, thereby demonstrating its prospective applications in the field of nonlinear optics. Variable-temperature crystal structural analysis combined with theoretical calculations revealed that the large NLO response stems from the inorganic SnCl₃ moiety, whereas the high-performance NLO switching properties mainly originate from the order/disorder transformation of the N-methylpyrrolidinium. This work provides a new approach to designing and exploring new high-performance quadratic NLO switches involving tin halide organic-inorganic hybrids.

Structural phase transition and dielectric anisotropy properties of a lead-free organic–inorganic hybrid

We presented a new inorganic–organic hybrid compound, which exhibits phase transition and dielectric anisotropy properties.

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.