Molecular Dynamics of Flexible Polar Cations in a Variable Confined Space: Toward Exceptional Two-Step Nonlinear Optical Switches

Coupling Narrow Band Gap and Switchable SHG Responses in a New Molecule Ferroelectric: Imidazolyl Propylamine Pentabromo Stibium(III)

Due to the existence of some cross properties such as SHG (second-harmonic generation), ferroelectricity, piezoelectricity, and thermoelectricity, molecular ferroelectrics have been widely used as a composite multipurpose material. Particularly, organic-inorganic molecular ferroelectrics have received much interest recently because of their unique flexible structures, friendly environment, ease of synthesis, etc. Also, these hybrids show great flexibility in band-gap engineering. Here we report a new molecular halide, [C₆H₁₃N₃SbBr₅]_n (1; C₆H₁₃N₃ = 1-(3-aminopropyl)imidazole), which experiences a unique ferroelectric to paraelectric phase transition at around 230 K from space group P2₁ to P2₁/c. Significantly, compound 1 exhibits a narrow band gap with a value of 2.52 eV, large pronounced SHG-active, perfect rectangle hysteresis loops with a large spontaneous polarization of 6.86 μC/cm². DSC (differential scanning calorimetry) and dielectric dependence on temperature tests and the volume change before and after the phase transition show that compound 1 is characterized by a second-order phase transition. These findings will contribute to the multifunctional materials field of organic-inorganic hybrids.

Chiral Switchable Low-Dimensional Perovskite Ferroelectrics

Low-dimensional hybrid organic-inorganic perovskites (HOIPs) possess more localized electronic states and narrower conduction and valence bands to promote self-trapping of excitons and stronger exciton emission; therefore, they are widely used as building blocks for various applications in the fields of optoelectronics, photovoltaics, light-emitting diodes, luminescence, fluorescence, and so forth. Despite the past decades of intensive study, the discovered low-dimensional chiral HOIPs are rare as of the 1D chiral HOIP single crystals reported in 2003, as well as the low-dimensional chiral HOIP ferroelectrics are particularly scarce since the first chiral two-dimensional (2D) and/or one-dimensional (1D) HOIP ferroelectrics reported. Herein, two new low-dimensional HOIPs with the same conformational formula [R-MPA]₂CdCl₄ (R-MPA⁺ = (R)-(-)-1-methyl-3-phenylpropylamine) were successfully synthetized by means of regulating the stoichiometric proportion of R-MPA and CdCl₂ in two ways of 1:1 (1) and 2:1 (2). By combining single-crystal X-ray diffraction, circular dichroism (CD) spectroscopy, differential scanning calorimetry, temperature-dependent dielectric constant, temperature-dependent second-harmonic generation (SHG) effect, polarization-dependent SHG response, and P-E hysteresis loop, we reveal that 1 is a 1D nonchiral molecular ferroelectric and 2 is the first zero-dimensional (0D) chiral ferroelectric with distinct CD signals; meanwhile, 2 exhibits increased properties of high-T_c, large dielectric constant, SHG isotropy, and ferroelectricity than that of 1. These results not only shed light on the high tunability of the low-dimensional HOIP ferroelectrics but also open up an avenue to explore multifunctional chiral ferroelectrics.

A hybrid hydrochromic molecular crystal applicable to invisible ink with high reversibility

Highly reversible hydrochromic behavior is realized in a novel hybrid molecular crystal by controlling the gain and loss of coordinated water.

An unprecedented hexagonal double perovskite organic-inorganic hybrid ferroelastic material: (piperidinium)2[KBiCl6]

An unprecedented A2MIMIIIX6-type double perovskite adopting a fully hexagonal BaNiO3-type structure, (piperidinium)2[KBiCl6], undergoes a 2/mF1[combining macron] ferroelastic phase transition at 285 K with a spontaneous strain of 0.0615, arising from the order-disorder transition of organic cations together with the synchronous displacement of inorganic chains.

Unique cation-template three-dimensional hybrid material demonstrates dielectric switchable response

The strict tolerance space of three-dimensional (3D) crystalline structures is still a significant challenge in the area of switching dielectrics in comparison with lower-dimensional structures. Generally, the function of crystalline materials can be given or adjusted by controlling the environment in which synthesis takes place or the packing rearrangement. Using this method, special functional enhancements or changes in the dielectrics can be realized by improving the synthetic strategies. Here, a 3D switchable dielectric compound [MeHdabco]K(BF4)3 was achieved by employing the temperature selective effect. In particular, its structure is completely different from the usual 3D perovskite structure, which is constructed using two different cation-template frameworks. Moreover, the 3D [MeHdabco]K(BF4)3 shows a structural phase transition at 358 K. The thermal analysis (differential scanning calorimetry (DSC)) and X-ray diffractometry results provided evidence of these phase changes. This work provides a feasible strategy that can be used to achieve the different structures of an 'isomer', and enrich the method used for designing diverse functional materials.

A polar oxyhalogen-vanadate compound (C5NH13Cl)2VOCl4 with optical and two-staged dielectric switch behavior

Polar organic-inorganic hybrid materials have been applied in ferroelectricity, as well as in devices based on nonlinear optical and piezoelectricity properties. Here, we used a rectangular pyramid structure of [VOCl4]2- to construct a polar compound (C5NH13Cl)2VOCl4 (1). Compound 1 crystallized in the monoclinic P21 space group. Coexistence of nonlinear optical switching behavior (space-group change from P21 to P21/n) and two-staged thermosensitive dielectric switching properties could be achieved under the stimulus of temperature. Our findings provide an effective approach for construction of polar materials.

Dielectric switching, SHG response and Pd(ii) adsorption of a multifunctional phase-transition complex

One-dimensional coordination polymer [(C2H4OH)C4H9NS]CdCl3 has the performance of dielectric switching and SHG response. And the compound can adsorb precious Pd(ii) and the adsorption could be monitored by dielectric anomaly and SHG signal.

Structural insights into a new family of three-dimensional thiocyanate-bridged molecular double perovskites

Four new three-dimensional thiocyanate-bridged molecular double perovskites with bent Cd–S–C angles in a narrow distribution range reveal highly distorted frameworks with a relatively strong structural rigidity.

Energy Harvesting and Pd(II) Sorption Based on Organic-Inorganic Hybrid Perovskites

Organic-inorganic hybrid perovskites are currently an active research topic in the field of energy and next-generation electronics. Their selectable organic and inorganic components provide infinite possibilities for designing functional materials with multiple applications. Herein, we present a new one-dimensional BaNiO₃-like organic-inorganic hybrid perovskite (thiazolidinium)CdBr₃ (1), which displays a phase transition at 263 K and a switchable second harmonic generation (SHG) response. Intriguingly, 1 shows a pyroelectric coefficient p_e of ∼0.6 μC·cm^-2·K^-1 and a piezoelectric output voltage of ∼2.0 V for our fabricated piezoelectric generation device, indicating its great potential for pyroelectric sensors, self-powered low-voltage electronic devices, and energy harvesters. Moreover, the presence of a specific thioether donor enables 1 to appropriately adsorb Pd(II) ions, which can be monitored by the corresponding change in phase transition behavior, SHG signal, and pyroelectric response. This work provides a new insight to develop new multifunctional materials, demonstrating the feasibility of utilizing organic-inorganic hybrid perovskites to realize future self-powered low-voltage devices and energy harvesters.

Organometallic-Based Hybrid Perovskite Piezoelectrics with a Narrow Band Gap

Hybrid organic-inorganic perovskites (HOIPs) with the general formula ABX₃ hold phenomenal research interest for their great scientific and technological potential in photovoltaic, piezoelectric, and electroluminescent devices. It is their considerable structural diversity that offers a good opportunity to build a variety of HOIP structures with various functionalities. However, no organometallic-based HOIP piezoelectrics have yet been found, despite the structural diversity and functional richness of organometallic compounds such as the ferrocene-based family. Here, for the first time, we report an organometallic-based HOIP piezoelectric, [(ferrocenylmethyl)trimethylammonium]PbI₃. Benefitting from the stability of ferrocene-based cations, excellent piezoelectric performance, comparable to that of LiNbO₃, can be obtained and optimized by tuning the anionic framework. The involvement of organometallic cations enables a narrow band gap of 2.37 eV, much lower than those of most HOIPs and some inorganic semiconductors. This work provides a new future direction for the study of perovskites and will inspire intriguing research on organometallic-based HOIP piezoelectrics.

Advances and Property Investigations of an Organic-Inorganic Ferroelectric: (diisopropylammonium)2[CdBr4]

The preparation of materials featuring more than one ferroelectric phase represents a promising strategy for controlling electrical properties arising from spontaneous polarization, since it offers an added advantage of temperature-dependent toggling between two different ferroelectric states. Here, we report on the discovery of a unique ferroelectric–ferroelectric transition in diisopropylammonium tetrabromocadmate (DPAC, (C₆H₁₆N)₂[CdBr₄]) with a T_c value of 244 K, which is continuous in nature. Both phases crystallize in the same polar orthorhombic space group, Iab2. The temperature-resolved second-harmonic-generation (SHG) measurements using 800 nm femtosecond laser pulses attest to the polar structure of DPAC on either side of the phase transition (PT). The dc conductivity parameters were estimated in both solid phases. The anionic substructure is in the form of [CdBr₄]^2– discrete complexes (0D), while in the voids of the structure, the diisopropylammonium cations are embedded. The ferroelectric properties of phases I and II have been confirmed by the reversible pyroelectric effect as well as by P–E loop investigations. On the basis of the dielectric responses, the molecular mechanism of the PT at 244 K has been postulated to be of mixed type with an indication of its displacive nature.

A novel ferroelectric crystal of (C₆H₁₆N)₂[CdBr₄] has been synthesized, and a description of its properties (thermal, structural, electric, second-harmonic generation) is presented. The ferroelectric properties in phases I and II have been successfully confirmed by the reversible pyroelectric effect as well as by P−E hysteresis loop investigations and SHG properties.

Giant and Broadband Multiphoton Absorption Nonlinearities of a 2D Organometallic Perovskite Ferroelectric

Multiphoton absorption (MPA) has been utilized for important technological applications. High-order multiphoton harvesting (e.g., five-photon absorption, 5PA) exhibits unique properties that could benefit biophotonics. Within this field, perovskite oxide ferroelectrics (e.g., BaTiO₃ ) enable low-order optical nonlinearities of 2PA/3PA processes. However, it is challenging to obtain efficient, high-order 5PA effects. Herein, for the first time, giant and broadband MPA properties are presented in the 2D hybrid perovskite ferroelectric (IA)₂ (MA)₂ Pb₃ Br₁₀ (1; IA = isoamylammonium and MA = methylammonium), where multiphoton-excited optical nonlinearities related to different MPA mechanisms over a broadband range of 550-2400 nm are observed. Strikingly, its 5PA absorption cross-section (σ₅ ) reaches up to 1.2 × 10^-132 cm¹⁰ s⁴ photon^-4 (at 2400 nm), almost 10 orders larger than some state-of-the-art organic molecules and a record-high value among all known ferroelectrics. This unprecedented 5PA effect results from the quantum-confined motif of inorganic trilayer sheets (wells) and organic cations (barriers) in 1. Moreover, its large ferroelectric polarization of 5 µC cm^-2 could promote modulation of MPA effects under external electric fields. As far as it is known, this is the first report on giant, broadband high-order MPA properties in ferroelectrics, which provides potential, novel electric-ordered materials for next-generation biophotonic applications.

Molecule-based nonlinear optical switch with highly tunable on-off temperature using a dual solid solution approach

Nonlinear optical switches that reversibly convert between on/off states by thermal stimuli are promising for applications in the fields of photoelectronics and photonics. Currently one main drawback for practical application lies in the control of their switch temperature, especially for the temperature range near room temperature. By mixed melting treatment, here we describe an alloy-like nonlinear optical switch with tunable switch temperature via a dual solid solution approach within the coordination polymer system. We initially prepare a coordination polymer (i-PrNHMe2)[Cd(SCN)3], which functions as a high-contrast thermoresponsive nonlinear optical switch originating from a phase transition at around 328 K. Furthermore, by taking advantage of a synergistic dual solid solution effect, the melt mixing of it with its analogue (MeNHEt2)[Cd(SCN)3], which features an unequal anionic chain templated by an isomeric ammonium, can afford coordination polymer solid solutions with switch temperatures that are tunable in a range of 273-328 K merely by varying the component ratio.

Enhancing switchable dielectric property for crystalline supramolecular rotor compounds by adding polar components

Two new compounds were obtained by assembling the [(2-methoxy-5-nitro-anilinium)(18-crown-6)]+ cation with non-polar PF6- and polar SO3CF3- anions, respectively. Benefiting from its polar anion, the SO3CF3- compound reveals a more significant dielectric switching behaviour during phase transition, demonstrating an effective strategy to enhance the dielectric property by adding polar components.

Regulating Reversible Phase Transition Behaviors by Poly-H/F Substitution in Hybrid Perovskite-Like 2[CH2FCH2NH3]·[CdCl4]

The molecular design and regulation has shown bright future for constructing smart molecular materials such as ferroelectrics, dielectric switches, electro-optic effect, and so forth. Here, by poly-H/F substitution in a simple organic-inorganic hybrid 2[CH₂FCH₂NH₃]·[CdCl₄], 1 (CH₂FCH₂NH₃ = fluorine ethylamine cation), we obtained two novel hybrids, namely, 2[CHF₂CH₂NH₃]·[CdCl₄], 2 (CHF₂CH₂NH₃ = 2,2'-difluorine ethylamine cation) and 2[CF₃CH₂NH₃]·[CdCl₄], 3 (CF₃CH₂NH₃ = 2,2',2″-trifluorine ethylamine cation). Further investigations show that compounds 1, 2, and 3 experience solid reversible phase transitions with temperatures at 294, 319, and 329 K respectively. These unique phase transitions were confirmed by their remarkable dielectric and heat anomalies around the phase transition temperatures. X-ray single-crystal diffraction analyses before and after the phase transitions show that the order-disorder motions of F atoms and the twist motions from the 2D [CdCl₄]^2- framework lead to these solid reversible phase transitions. Also, the Hirshfeld surface calculation of compounds 1, 2, and 3 suggests that the increasing ratio of the F···F interaction from the intermolecular interaction makes a major contribution for the substantial increase of their phase transition temperatures.

An Above-Room-Temperature Molecular Ferroelectric: [Cyclopentylammonium]2CdBr4

Molecular ferroelectrics as alternatives to the conventional inorganic ferroelectrics have been greatly developed in past decades; many of these have been discovered and designed through various chemical means due to their structural adjustability. However, it is still a huge challenge to obtain high (above room temperature) Curie temperature (T_c) molecular ferroelectrics to meet the application requirements. Here, we present a new organic-inorganic hybrid molecular ferroelectric, [cyclopentylammonium]₂CdBr₄ (1), showing a moderate above-room-temperature T_c of 340.3 K. The mechanism of the ferroelectric phase transition from Pnam to Pna2₁ in 1 is ascribed to the order-disorder transition of both the organic cations and inorganic anions, affording a spontaneous polarization of 0.57 μC/cm² for the ferroelectric phase. Using piezoresponse force microscopy (PFM), we clearly observed the antiparallel 180° stripe domains and realized the polarization switching, unambiguously establishing the existence of room-temperature ferroelectricity in the thin film. These attributes make it attractive for use in flexible devices, soft robotics, biomedical devices, and other applications.

Bistable molecular materials with dynamic structures

In this Feature Article, we introduce how to manipulate the motion of electrons or molecules by external stimuli, to achieve switchable properties in molecule-based single crystals.

Nitroprusside as a promising building block to assemble an organic–inorganic hybrid for thermo-responsive switching materials

A new nitroprusside-based hybrid (Me₂NH₂)[KFe(CN)₅(NO)] exhibits thermo-responsive switching behaviours on uniaxial expansivity and SHG signal owing to flexible host–guest hydrogen bonds and the synchronously deformable inorganic framework.

Optical-Dielectric Duple Bistable Switches: Photoluminescence of Reversible Phase Transition Molecular Material

Molecular optical-dielectric duple bistable switches are photoelectric (dielectric and fluorescent) multifunctional materials that can simultaneously convert optical and electrical signals in one device for seamless integration. However, exploring optical-dielectric duple channels of dielectric and photoluminescence is still a bigger challenge than single dielectric or photoluminescence bistable ones, which are hardly reported but probably will be heavily researched owing to the new generation artificial intelligence development needs in the future. Herein, a new optical-dielectric duple bistable switches material, [(CH₃ )₃ NCH₂ CH₃ ]₂ MnCl₄ (I), was obtained by a simple method for volatilization of solvents. Variable temperature single crystal X-ray analysis indicates that material I has a reversible bistable structure (order-disorder structure phase transition) corresponding to switching "ON'' and "OFF''. Unlike the single dielectric bistable structures that were previously reported, material I also own bistable features in terms of fluorescence property. This material enriches the specific examples of photoelectric duple function switch materials and facilitates the development of required devices.

H/F-Substitution-Induced Homochirality for Designing High-Tc Molecular Perovskite Ferroelectrics

A ferroelectric with a high phase-transition temperature (T_c ) is an indispensable condition for practical applications. Over the past decades, both strain engineering and the isotope effect have been found to effectively improve the T_c within ferroelectric material systems. However, the former strategy seems to prefer working in inorganic ferroelectric thin films, while the latter is also limited to some certain systems, such as hydrogen-bonded ferroelectrics. It is noted that a mono-fluorinated molecule is geometrically very similar to its parent molecule and the substitution of H by an F atom can introduce a chiral center on the molecule to template or stabilize polar structures. Significantly, the barrier of rotation of the fluorinated organic molecules is raised, resulting in a remarkable increase in T_c . Herein, by applying the molecular design strategy of H/F substitution to the organic-inorganic perovskite ferroelectric (pyrrolidinium)CdCl₃ with a low T_c of 240 K, two high-T_c chiral perovskite ferroelectrics, (R)- and (S)-3-F-(pyrrolidinium)CdCl₃ are successfully synthesized, for which the T_c reaches 303 K. The significant enhancement of 63 K in T_c extends the ferroelectric working temperature range to room temperature. This finding provides a new effective way to regulate the T_c in ferroelectrics and to design high-T_c molecular ferroelectrics.

The First 2D Homochiral Lead Iodide Perovskite Ferroelectrics: [R- and S-1-(4-Chlorophenyl)ethylammonium]2 PbI4

2D organic-inorganic lead iodide perovskites have recently received tremendous attention as promising light absorbers for solar cells, due to their excellent optoelectronic properties, structural tunability, and environmental stability. However, although great efforts have been made, no 2D lead iodide perovskites have been discovered as ferroelectrics, in which the ferroelectricity may improve the photovoltaic performance. Here, by incorporating homochiral cations, 2D lead iodide perovskite ferroelectrics [R-1-(4-chlorophenyl)ethylammonium]₂ PbI₄ and [S-1-(4-chlorophenyl)ethylammonium]₂ PbI₄ are successfully obtained. The vibrational circular dichroism spectra and crystal structural analysis reveal their homochirality. They both crystalize in a polar space group P1 at room temperature, and undergo a 422F1 type ferroelectric phase transition with transition temperature as high as 483 and 473.2 K, respectively, showing a multiaxial ferroelectric nature. They also possess semiconductor characteristics with a direct bandgap of 2.34 eV. Nevertheless, their racemic analogue adopts a centrosymmetric space group P2₁ /c at room temperature, exhibiting no high-temperature phase transition. The homochirality in 2D lead iodide perovskites facilitates crystallization in polar space groups. This finding indicates an effective way to design high-performance 2D lead iodide perovskite ferroelectrics with great application prospects.

Higher-Temperature Dielectric Molecular Motor Induced by Unusual Chair-to-Rotator Motion

With regard to the artificial molecular motor that was recognized with the 2016 Nobel Prize, this success proves the great scientific significance of rotary motor-type motion at the molecular level, which has been expected to play an invaluable role in the development of electronic information molecular materials. However, designing electronic information-critical high-temperature molecular motors has always been a huge challenge. Since we discovered [(CH₃)₃NCH₂Cl]MnCl₃, this cation rotation pattern with a motor-type motion structure has continued to attract our attention. Considering a strategy that combines molecular machines with dielectric theory, ( N, N-dimethylpiperidinium)CdCl₃, the new dielectric molecular motor material that exhibits superior physical properties, could be considered to be an excellent dielectric switch based on its electric field and temperature. Crystal structure analyses reveal that the reversible phase transition is mainly induced by the unusual chair-to-rotator motion of cations. Because of the unprecedented leaping structural transition from P6₃/ mmc to P2₁/ c and the rotating motor-type motion structure, the material exhibits remarkable anisotropy and outstanding dielectric switching characteristics. These findings open a new avenue for the design and assembly of novel molecular motor materials in the field of electronic information.

A molecular perovskite solid solution with piezoelectricity stronger than lead zirconate titanate

Piezoelectric materials produce electricity when strained, making them ideal for different types of sensing applications. The most effective piezoelectric materials are ceramic solid solutions in which the piezoelectric effect is optimized at what are termed morphotropic phase boundaries (MPBs). Ceramics are not ideal for a variety of applications owing to some of their mechanical properties. We synthesized piezoelectric materials from a molecular perovskite (TMFM)x(TMCM)1–xCdCl3 solid solution (TMFM, trimethylfluoromethyl ammonium; TMCM, trimethylchloromethyl ammonium, 0 ≤ x ≤ 1), in which the MPB exists between monoclinic and hexagonal phases. We found a composition for which the piezoelectric coefficient d33 is ~1540 picocoulombs per newton, comparable to high-performance piezoelectric ceramics. The material has potential applications for wearable piezoelectric devices.

Bunching and Immobilization of Ionic Liquids in Nanoporous Metal-Organic Framework

Room-temperature ionic liquids (ILs) are a unique, novel class of designer solvents and materials with exclusive properties, attracting substantial attention in fields like energy storage and supercapacitors as well as in ion-based signal processing and electronics. For most applications, ILs need to be incorporated or embedded in solid materials like porous hosts. We investigate the dynamic structure of ILs embedded in well-defined pores of metal-organic frameworks (MOFs). The experimental data combined with molecular dynamics simulations unveil astonishing dynamic properties of the IL in the MOF nanoconfinement. At low IL loadings, the ions drift in the pores along the electric field, whereas at high IL loadings, collective field-induced interactions of the cations and anions lead to blocking the transport, thus suppressing the ionic mobility and tremendously decreasing the conductivity. The mutual pore blockage causes immobilized ions in the pores, resulting in a highly inhomogeneous IL density and bunched-up ions at the clogged pores. These results provide novel molecular-level insights into the dynamics of ILs in nanoconfinement, significantly enhancing the tunability of IL material properties.

Switching hydrogen bonds to readily interconvert two room-temperature long-term stable crystalline polymorphs in chiral molecular perovskites

Two room-temperature polymorphic forms could be long-term stable yet easily interconvertible by switching the inter-cationic H-bonds in chiral molecular perovskites.

A new ferroelastic hybrid material with a large spontaneous strain: (Me3NOH)2[ZnCl4]

A new organic–inorganic hybrid undergoes a ferroelastic phase transition at 351 K accompanied with a large spontaneous stain.

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.

High-temperature ferroelastic phase transition in a perovskite-like complex: [Et4N]2[PbBr3]2

A new lead-bromide hybrid organic–inorganic complex [Et₄N]₂[PbBr₃]₂ (Et = ethyl) was synthesized, and its crystal structures could be described as a distorted perovskite-like one (at room temperature phase and at high temperature phase) and a step-like dielectric anomaly was obtained at around 375 K upon heating and 367 K upon cooling. It underwent a reversible structural phase transition with the Aizu notation of 6/mmmF2/m belonging to one of the 94 species of ferroelastic phase transitions, displayed switchable dielectric behaviors triggered by the motion or reorientation of the tetraethylammonium cations and the displacement of Pb²⁺ and Br⁻ ions in a solid-state crystal. Ferroelastic domain walls were also observed in atomic-force microscopy. Differential scanning calorimetry, dielectric measurements and variable-temperature X-ray structure determinations indicated this complex exhibited a dielectric anomaly associated with the structural phase transition. All of these demonstrate its potential application as a temperature switchable molecular dielectric material in the ferroic-related field.

A new lead-bromide hybrid organic–inorganic complex [Et₄N]₂[PbBr₃]₂ (Et = ethyl) was synthesized, and its crystal structures could be described as a distorted perovskite-like one and a step-like dielectric anomaly was obtained at around 375/367 K.

Above room-temperature dielectric and nonlinear optical switching materials based on [(CH3)3S]2[MBr4] (M = Cd, Mn and Zn)

Three organic–inorganic hybrid compounds based on [Me₃S]⁺ cations exhibit sensitive dielectric and nonlinear optical switching characteristics above room temperature.

Doping induced dielectric anomaly below the Curie temperature in molecular ferroelectric diisopropylammonium bromide

A dielectric anomaly induced by doping has been observed at about 340 K in chlorine-doped diisopropylammonium bromide. The dielectric anomaly has a switchable behaviour, which indicates potential applications on switches and sensors. Temperature-dependent Raman spectrum, X-ray diffraction and differential scanning calorimetry do not show any anomaly around the dielectric anomaly temperature, which prove that the dielectric anomaly does not come from structure phase transition and has no specific heat variety. It is assumed that this dielectric anomaly can be attributed to the freezing of ferroelectric domain walls induced by the pinning of point defects.

Unusual high-temperature reversible phase transition containing dielectric and nonlinear optical switches in host-guest supramolecular crown ether clathrates

A novel high-temperature dielectric and quadratic nonlinear optical switching material, 3,4-difluoroanilinium 18-crown-6 perchlorate, was synthesized. It exhibits two successive structural phase transitions at 347 K and 240 K, respectively. Gradually increased SHG-active characteristics are also identified.

A lead-free perovskite-like hybrid with above-room-temperature switching of quadratic nonlinear optical properties

We report a new lead-free perovskite-like hybrid, composed of hexamethyleneimine and one-dimensional [SbCl5]n2- polyanionic zigzag chains, which shows above-room-temperature switching of quadratic nonlinear optical (NLO) properties induced by the unique order-disorder conformational changes of the organic cation.

Alloying n-Butylamine into CsPbBr3 To Give a Two-Dimensional Bilayered Perovskite Ferroelectric Material

Cesium-lead halide perovskites (e.g. CsPbBr₃ ) have gained attention because of their rich physical properties, but their bulk ferroelectricity remains unexplored. Herein, by alloying flexible organic cations into the cubic CsPbBr₃ , we design the first cesium-based two-dimensional (2D) perovskite ferroelectric material with both inorganic alkali metal and organic cations, (C₄ H₉ NH₃ )₂ CsPb₂ Br₇ (1). Strikingly, 1 shows a high Curie temperature (T_c =412 K) above that of BaTiO₃ (ca. 393 K) and notable spontaneous polarization (ca. 4.2 μC cm^-2 ), triggered by not only the ordering of organic cations but also atomic displacement of inorganic Cs⁺ ions. To our knowledge, such a 2D bilayered Cs⁺ -based metal-halide perovskite ferroelectric material with inorganic and organic cations is unprecedented. 1 also shows photoelectric semiconducting behavior with large "on/off" ratios of photoconductivity (>10³ ).

Room-temperature optic-electric duple bistabilities induced by plastic transition

A plastic crystal simultaneously exhibits room-temperature bistabilities in two physical channels: dielectric and nonlinear optics.