Design and Prominent Dielectric Properties of a Layered Phase-Transition Crystal: (Cyclohexylmethylammonium)₂CdCl₄

Abstract

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...

Unprecedented Dielectric Bistable Switching in a Binuclear HgII Based Hybrid Compound

“…Over the past two decades, great advances have been made experimentally and theoretically for a few crystalline metal‐organic complexes in solid and liquid phase, including plenty of reported solid‐state polycrystalline dielectric switches, which gradually become one of the research hotspots in the materials science and electronics . As is well‐known, a previously utilized and prominent architectural design strategies for assembling tunable molecular dielectrics is to optimize conformation of polar or flexible moieties into functional blocks for the sake of probing the convertible dielectric behaviors . For instance, as well‐designed MOF‐based switchable dielectrics, [(CH 3 ) 2 NH 2 ] 2 [KCo(CN) 6 ] and (HIm) 2 [KCo(CN) 6 ] (HIm = imidazolium cation), their structures can be finely tuned by incorporating mobile guest molecules with well‐fitted rigid cavities , .…”

Temperature‐Induced Reversible Phase Transition with Switchable Dielectric Response in a A2BX4‐Type Hybrid Compound: [TEAMA]2[CdBr4] (TEAMA=(CH3CH2)3NCH3)

“…It is known that dipolar reorientation in crystal lattices contributes greatly to various‐temperature dielectric response, which is also an indicator of thermally activated molecular rotations and structural phase transition [26–30] . As mentioned above, the order‐disorder transition of [TEAMA] + cations would arouse a switchable property of dielectric constant.…”

Phase transition and switchable dielectric behaviours in an organic–inorganic hybrid compound: (3-nitroanilinium) 2 (18-crown-6) 2 (H 2 PO 4 ) 2 (H 3 PO 4 ) 3 (H 2 O)

“…The structural units of compound 1 used in the calculations were (3-nitroanilinium) 3 (18-crown-6) 3 (H 2 PO 4 ) 2 and (3-nitroanilinium) 3 (18-crown-6) 3 , which differ from the actual stoichiometry of the compound to make the calculations computationally tractable. These computations were based on the fixed atomic coordinates obtained from the crystal structure at 296 K. The relative energy was calculated by evaluating the rigid rotation of the C (25) -N (1) bond axes in 308 increments (electronic supplementary material, figure S9a). The nearest-neighbour molecules around the nitro-group ( -NO 2 ) of the 3-nitroanilinium cation were included in the calculation of the potential energy curves (electronic supplementary material, figure S9b and S9c).…”