The organic–inorganic hybrid compound NH3(CH2)5NH3MnCl4 exhibits a phase transition at 298 K, coupled with switchable dielectric and photoluminescence performances.
Molecular optical-electrical duple switches (switch "ON" and "OFF" bistable states) represent a class of highly desirable intelligent materials because of their sensitive switchable physical and/or chemical responses, simple and environmentally friendly processing, light weights, and mechanical flexibility. In the current work, the phase transition of 1 (general formula R2MX5, [C5N2H16]2[SbBr5]) can be triggered by the order-disorder transition of the organic cations at 278.3 K. The temperature-induced phase transition causes novel bistable optical-electrical duple characteristics, which indicates that 1 might be an excellent candidate for a potential switchable optical-electrical (fluorescence/dielectric) material. In the dielectric measurements, remarkable bistable dielectric responses were detected, accompanied by striking anisotropy along various crystallographic axes. For the intriguing fluorescence emission spectra, the intensity and position changed significantly with the occurrence of the structural phase transition. We believe that these findings might further promote the application of halogenoantimonates(III) and halogenobismuthates(III) in the field of optoelectronic multifunctional devices.
A novel zigzag chain organic-inorganic hybrid compound of the general formula R2MI5, [n-C3H7NH3]2[SbI5] (1), was successfully synthesized, in which the n-propylammonium cations were located in the free cavities between the one-dimensional zigzag chains. Systematic characterization was performed to investigate the phase transition of 1. A pair of sharp peaks at 211.8 K (heating) and 203.7 K (cooling) with a hysteresis 8.1 K were observed in the differential scanning calorimetry (DSC) curve, indicating the first-order phase transition behavior of 1. The temperature dependence dielectric measurement demonstrated a step-like change at around 211.8 K, which makes 1 a potential switchable dielectric material. Frequency dependence measurement revealed that the frequency exerts a weak influence on the dielectric permittivity. Further structural analysis shows that both anionic and cationic moieties contribute to the phase transition, accompanied by weak hydrogen bond interactions between cations and the [SbI5]n(2-) chains.
Following our recent finding of interesting dielectric and ferroelectric properties in semiconducting organic−inorganic layered perovskites (benzylammonium) 2 PbCl 4 and (cyclohexylammonium) 2 PbBr 4−4x I 4x (x = 0−1), we designed a new layered perovskite-type crystal (cyclohexylmethylammonium) 2 CdCl 4 . By systematic characterizations, including differential scanning calorimetry measurements, dielectric measurements, and variable-temperature structural analysis, this crystal was found to undergo a reversible first-order phase transition at around T c = 342 K. The origin of the phase transition is associated with the order− disorder change of the organic cation as expected. The phase transition is accompanied by the anticipated large dielectric constant change and remarkable dielectric anisotropy. These dielectric performances reveal potential application of the crystal as a high-temperature dielectric material. More interesting dielectric crystals are expected to be tailored in the future by taking advantage of the richness of layered perovskites. ■ INTRODUCTIONOwing to the high potential of producing materials with novel properties, organic−inorganic hybrid compounds are currently a hot topic of research. 1−5 Recently, their study was extended to structural phase transitions, and a few interesting phase transition properties were found. 6−12 The key components are the included organic cations, which have a large degree of motion in the cavities enclosed by the inorganic parts, exhibit dynamical disorder at relatively high temperatures, and become ordered below particular temperatures, giving rise to symmetry breaking and structural phase transitions. 13−16 Structural phase transitions in crystals are generally accompanied by changes of physical properties and, in many cases, can lead to intriguing physical properties, such as ferroelectric, dielectric, and electromechanical properties. 17,18 Therefore, the design of organic−inorganic hybrid crystals with structural phase transitions is very important, not only for the theoretical study of structure−property relationships, but also for the exploration of novel physical properties. 19−22 We have recently demonstrated that structural phase transitions in two-dimensional (2D) lead-halide layered perovskites can lead to interesting ferroelectric and dielectric properties, which produces molecular semiconducting ferroelectricity. 23,24 2D metal-halide layered perovskites with the general formula (R-NH 3 ) 2 MX 4 , where R is any alkyl or aromatic group and M is any divalent metal, have been intensely studied in the last two decades, because these crystals exhibit a number of appealing features suitable for a wide range of applications, such as solid-state batteries, ionic conductors, sensors, photovoltaic cells, luminescent devices, and so on. 25−28 Combination of the phase transition properties and physical properties of the 2D perovskites may lead to new materials and devices for photovoltaics, spintronics, and electrical-mechanical sensing. However, the study i...
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