Large Electrostrictive Coefficient in a Two-Dimensional Hybrid Perovskite Ferroelectric

Chlorine Substitution in Spirocyclic Derivatives Triggers SHG Response in Noncentrosymmetric Crystal

Organic-inorganic hybrid phase transition materials with switchable properties have important potential applications in smart devices such as dielectric switches and storage. Nevertheless, it remains challenging to modify molecular structures efficiently to obtain materials simultaneously possessing multiple responsive properties. Herein, different from ordinary halogen substitutions in Metal Halide, we report a halogen regulation design of organic molecular strategy: (ASD) 2 MnBr 4 (ASD=5-azonia-spiro [4.5] decane) to (CASD) 2 MnBr 4 (CASD=8-chloro-5-azonia-spiro [4.5] decane). After organic molecular halogen regulation, the SHG response was excited and the dielectric phase transition temperature ( T c ) has also been greatly improved. Furthermore, under the irradiation of UV lamp, both showed green light with quantum yields above 50%. This work is of great significance for further exploration of multifunctional molecular switch materials through halogen modification strategies.

Rational Design of Molecular Ferroelectrics with Negatively Charged Domain Walls

Ferroelectric domains and domain walls are unique characteristics of ferroelectric materials. Among them, charged domain walls (CDWs) are a special kind of peculiar microstructure that highly improve conductivity, piezoelectricity, and photovoltaic efficiency. Thus, CDWs are believed to be the key to ferroelectrics' future application in fields of energy, sensing, information storage, and so forth. Studies on CDWs are one of the most attractive directions in conventional inorganic ferroelectric ceramics. However, in newly emerged molecular ferroelectrics, which have advantages such as lightweight, easy preparation, simple film fabrication, mechanical flexibility, and biocompatibility, CDWs are rarely observed due to the lack of free charges. In inorganic ferroelectrics, doping is a traditional method to induce free charges, but for molecular ferroelectrics fabricated by solution processes, doping usually causes phase separation or phase transition, which destabilizes or removes ferroelectricity. To realize stable CDWs in molecular systems, we designed and synthesized an n-type molecular ferroelectric, 1-adamantanammonium hydroiodate. In this compound, negative charges are induced by defects in the I^- vacancy, and CDWs can be achieved. Nanometer-scale CDWs that are stable at temperatures as high as 373 K can be "written" precisely by an electrically biased metal tip. More importantly, this is the first time that the charge diffusion of CDWs at variable temperatures has been investigated in molecular ferroelectrics. This work provides a new design strategy for n-type molecular ferroelectrics and may shed light on their future applications in flexible electronics, microsensors, and so forth.

Efficient Piezoelectric Energy Harvesting from a Discrete Hybrid Bismuth Bromide Ferroelectric Templated by Phosphonium Cation

Bismuth containing hybrid molecular ferroelectrics are receiving tremendous attention in recent years owing to their stable and non-toxic composition. However, these perovskite-like structures are primarily limited to ammonium cations. Herein, we report a new phosphonium based discrete perovskite-like hybrid ferroelectric with a formula [Me(Ph)₃ P]₃ [Bi₂ Br₉ ] (MTPBB) and its mechanical energy harvesting capability. The Polarization-Electric field (P-E) measurements resulted in a well-defined ferroelectric hysteresis loop with a remnant polarization value of 2.1 μC cm^-2 . Piezoresponse force microscopy experiments enabled visualization of the ferroelectric domain structure and evaluation of the piezoelectric strain coefficient (d₃₃ ) for an MTPBB single crystal and thin film sample. Furthermore, flexible devices incorporating MTPBB in polydimethylsiloxane (PDMS) matrix at various concentrations were fabricated and explored for their mechanical energy harvesting properties. The champion device with 20 wt % of MTPBB in PDMS rendered a maximum peak-to-peak open-circuit voltage of 22.9 V and a maximum power density of 7 μW cm^-2 at an optimal load of 4 MΩ. Moreover, the potential of MTPBB-based devices in low power electronics was demonstrated by storing the harvested energy in various electrolytic capacitors.

Prospects of Metal-Free Perovskites for Piezoelectric Applications

Metal-halide perovskites have emerged as versatile materials for various electronic and optoelectronic devices such as diodes, solar cells, photodetectors, and sensors due to their interesting properties of high absorption coefficient in the visible regime, tunable bandgap, and high power conversion efficiency. Recently, metal-free organic perovskites have also emerged as a particular class of perovskites materials for piezoelectric applications. This broadens the chemical variety of perovskite structures with good mechanical adaptability, light-weight, and low-cost processability. Despite these achievements, the fundamental understanding of the underlying phenomenon of piezoelectricity in metal-free perovskites is still lacking. Therefore, this perspective emphasizes the overview of piezoelectric properties of metal-halide, metal-free perovskites, and their recent progress which may encourage material designs to enhance their applicability towards practical applications. Finally, challenges and outlooks of piezoelectric metal-free perovskites are highlighted for their future developments.

Realization of In-Plane Polarized Light Detection Based on Bulk Photovoltaic Effect in A Polar Van Der Waals Crystal

2D van der Waals materials are widely explored for in-plane polarized light detection owing to their distinctive in-plane anisotropic feature. However, most of these polarized light-sensitive devices root in their low symmetry of in-plane structure and work depending on external power sources, which greatly impedes the simplification of integrated devices and sustainable development. Bulk photovoltaic effect (BPVE), which separates photoexcited carriers via built-in electric field without an external power source and shows an angle-dependence on light polarization, is promising for self-powered polarized light detection to break through the restriction of in-plane anisotropy. Herein, a 2D lead-free van der Waals perovskite (Cl-PMA)₂ CsAgBiBr₇ (1, Cl-PMA = 4-Chlorobenzylamine) is successfully designed through the dimension reduction strategy. 1 exhibits BPVE with an open-circuited photovoltage up to ≈0.5 V. Driven by the BPVE, self-powered in-plane polarized light detection with a large polarization ratio of 1.3 is obtained for 1. As far as it is known, the first in-plane polarized light detection in hybrid perovskites based on BPVE is realized here. This work highlights the strategy of designing lead-free hybrid perovskite with BPVE and opens an avenue for exploiting in-plane highly sensitive polarized light detection in 2D van der Waals materials.

Chiral Hybrid Copper(I) Halides for High Efficiency Second Harmonic Generation with a Broadband Transparency Window

Chiral hybrid organic-inorganic metal halides (HOMHs) with intrinsic noncentrosymmetry have shown great promise for applications in second-order nonlinear optics (NLO). However, established chiral HOMHs often suffer from their relatively small band gaps, which lead to negative impacts on transparent window and laser-induced damage thresholds (LDT). Here, we have synthesized two chiral HOMHs based on Cu^I halides, namely (R-/S-MBA)CuBr₂ , which feature well-balanced NLO performances with a highly efficient SHG response, outstanding optical transparency, and high LDT. The effective second-order NLO coefficient of (R-MBA)CuBr₂ has been determined to be ≈24.7 pm V^-1 , which is two orders of magnitude higher than that of their Cu^II counterparts. This work shows the promising potential of Cu^I -based chiral HOMHs for nonlinear photonic applications in wide wavelength regions.

Piezoelectric energy harvesting of a bismuth halide perovskite stabilised by chiral ammonium cations

A chiral Bi(iii) 1D-perovskite {[sCH(MePh)(Me)NH3][BiBr5]}n was synthesized and shown to exhibit piezoelectric polarization. Flexible polymer composites of it were prepared and utilized for the fabrication of nanogenerator devices.

A Cd-based perovskite with optical-electrical multifunctional response

Two-dimensional (2D) organic-inorganic hybrid perovskites (OIHPs) have drawn tremendous attention on account of their structural tunability, simple synthesis mothed, superior properties. Among them, 2D cadmium-based perovskites, exhibiting reversible phase transition,...

The construction of a two-dimensional organic–inorganic hybrid double perovskite ferroelastic with a high Tc and narrow band gap

Two-dimensional (2D) hybrid double perovskites have attracted extensive research interest for their fascinating physical properties, such as ferroelectricity, X-ray detection, light response and so on. In addition, ferroelastics, as an important branch of ferroic materials, exhibits wide prospects in mechanical switches, shape memory and templating electronic nanostructures. Here, we designed a 2D phase-transition double perovskite ferroelastic through a structurally progressive strategy. This evolution is core to our construction process from 0D to 1D and AgBi-based 2D. In this way, we successfully synthesized 2D lead-free ferroelastic (DPA)₄AgBiBr₈ (DPA = 2,2-dimethylpropan-1-aminium) with a high Curie temperature (T_c), which shows a narrower band gap than 0D (DPA)₄Bi₂Br₁₀ and 1D (DPA)₅Pb₂Br₉. Moreover, the mechanism of structural phase transition and molecular motion are fully characterized by temperature dependent solid-state NMR and single crystal XRD. (DPA)₄AgBiBr₈ injects power into the discovery of new ferroelastics or the construction and dimensional adjustment in new hybrid double perovskites.

By using a lead-free AgBi-based scheme, we successfully synthesized a two-dimensional double perovskite ferroelastic (DPA)₄AgBiBr₈ with high T_c of 375 K and a narrow band gap of 2.44 eV, where DPA is 2,2-dimethylpropan-1-aminium.

Unusual high-temperature host–guest inclusion compound-based ferroelectrics with nonlinear optical switching and large spontaneous polarization behaviours

Host–guest inclusion compound-based ferroelectrics [Hcta-(18-crown-6)]+[BF4]− (1) and [Hcta-(18-crown-6)]+[ClO4]− (2) with a high Curie temperature (Tc = 403/394 K) and large spontaneous polarization (Ps = 5.7/4.7 μC cm−2) are reported.

Ferroic phase transition molecular crystals

Ferroic phase transition molecular crystals (FPTMCs), i.e., ferroelectrics and ferroelastics, are an important family of functional molecular materials, having merits of easy synthesis, structural tunability and flexibility, and biocompatibility. Both...

Tunable hybrid perovskites with Narrow bandgap and Multistage phase transition properties: 2,2-difluoroethylamine·Antimony Hexabromide

Zero-dimensional perovskites have received extensive attention in recent years due to their unique structures, such as large exciton binding energy, strong quantum confinement effect, and good stability. Precisely construct target...

Thermally stimuli-responsive materials with transformable double channels of nonlinear optical and dielectric

Organic-inorganic hybrid materials have received extensive attention and in-depth research in the past few decades due to their superior properties and potential applications in storage, sensing, dielectric switches, actuators and...

Solvent-induced reversible high-temperature phase transition in crown ether clathrates

The phase transitions of crown ether complexes with molecular motor motion triggered by the solvent-induced effect are reported.

High-Temperature Phase Transition Containing Switchable Dielectric Behavior, Long Fluorescence Lifetime, and Distinct Photoluminescence Changes in a 2D Hybrid CuBr4 Perovskite

A novel organic-inorganic hybrid perovskite crystal, [ClC₆H₄(CH₂)₂NH₃]₂CuBr₄ (1), having experienced an invertible high-temperature phase transition near T_c (the Curie temperature T_c = 355 K), has been successfully synthesized. The phase-transition characteristics for compound 1 are thoroughly revealed by specific heat capacity (C_p), differential thermal analysis, and differential scanning calorimetry tests, possessing 16 K broad thermal hysteresis. Multiple-temperature powder X-ray diffraction analysis further proves the phase-transition behavior of compound 1. Moreover, compound 1 exhibits a significant steplike dielectric response near T_c, revealing that it can be deemed to be a promising dielectric switching material. The variable-temperature fluorescence experiments show distinct photoluminescence (PL) changes of compound 1. Further investigation and calculation disclose that the fluorescence lifetime of compound 1 can reach as long as 55.46 μs, indicating that it can be a potential PL material. All of these researches contribute a substitutable avenue in the design and construction of neoteric phase-transition compounds combining high Curie temperature and PL properties.

Tuning Dielectric Transitions in Two-Dimensional Organic-Inorganic Hybrid Lead Halide Perovskites

Organic-inorganic hybrid metal halide perovskites possessing unique two-dimensional (2D)-layered structures have been demonstrated with excellent molecular tunability and stability, especially the promising semiconductor properties for solar cell applications. In this work, three 2D lead halide organic-inorganic hybrid perovskites (IAA)₂PbX₄ (IAA = isoamylammonium cation and X = Cl, Br, and I) were synthesized by employing a solution processing method and demonstrate distinct tuning solid-state phase transitions coupled with dielectric responses, as well as light absorption properties. Among the title perovskites, the phase transition temperature decreases gradually, and their band gap also indicates a narrowing trend. The results are mainly derived from slight changes in the crystal structure by halogen regulation. These findings might provide an effective crystal engineering strategy for exploring high-performance functional perovskite materials.

Ferroelectric properties, narrow band gap and ultra-large reversible entropy change in a novel nonlinear ionic chromium(VI) compound

A novel chromium(VI)-based compound, [(CH₃CH₂)₃N(CH₂Cl)][CrO₃Cl] (1), undergoes a high-temperature phase transition at around 340.9 K, accompanied by an ultra-large entropy change of 63.49 J mol^-1 K^-1. Compound 1 exhibits a moderate ferroelectric polarization of 0.48 μC cm^-2 and a remarkable CD signal. Strikingly, 1 occupies a narrow band gap of 2.22 eV, which is chiefly attributed to the inorganic [CrO₃Cl]^- tetrahedron. It is believed that these findings will contribute to an alternative pathway for the design of multifunctional ferroelectric materials, whose potential applications will be in semiconductors, energy storage, etc.

High-Curie Temperature Multilayered Hybrid Double Perovskite Photoferroelectrics Induced by Aromatic Cation Alloying

Due to the breakthrough development of layered hybrid perovskites, the multilayered hybrid double perovskites have emerged as outstanding semiconducting materials owing to their environmental friendliness and superior stability. Despite recent booming advances, the realization of above-room temperature ferroelectricity in this fascinating family remains a huge challenge. Herein, when the molecular design strategy of aromatic cation alloying is applied, an above-room temperature "green" bilayered hybrid double perovskite photoferroelectric, (C₆H₅CH₂NH₃)₂CsAgBiBr₇ (BCAB), is successfully developed with a notable saturation polarization of 10.5 μC·cm^-2 and high-Curie temperature (T_c ∼ 483 K). Strikingly, such a T_c achieves a new record in multilayered hybrid perovskite ferroelectrics, which extends the ferroelectric working temperature to a high level. Further computational investigation reveals that the high-T_c originated from the high phase-transition energy barrier switched by the rotation of the aromatic cation in the confined environment of the inorganic layers. In addition, benefiting from the attractive polarization and remarkable photoelectric properties, a bulk photovoltaic effect (BPVE) with a prominent zero-bias photocurrent (2.5 μA·cm^-2) is achieved. As far as we know, such a high-T_c multilayered hybrid double perovskite ferroelectric is unprecedented, which sheds light on the rational design of an environmental photoferroelectric for high performance photoelectric devices.

One-Step Electrochemical Growth of 2D/3D Zn(II)-MOF Hybrid Nanocomposites on an Electrode and Utilization of a PtNPs@2D MOF Nanocatalyst for Electrochemical Immunoassay

To date, two-dimensional (2D) and three-dimensional (3D) metal organic frameworks (MOFs) have been promising materials for applications in electrocatalysis, separation, and sensing. However, the exploration of a simple method for simultaneous fabrication of 2D/3D MOFs on a surface remains challenging. Herein, a one-step and in situ electrosynthesis strategy for fabrication of 2D Hemin-bridged MOF sheets (Hemin-MOFs) or 2D/3D Zn(II)-MOF hybrid nanocomposites on an electrode is reported. It exhibits varied morphologies at different electrodeposition times and attains a 2D/3D complex morphology by adding 1,3,5-benzenetricarboxylic acid (H₃BTC) as an organic ligand. The morphology and size of 2D Hemin-MOFs are important factors that influence their performance. Since Pt nanoparticles (PtNPs) are grown on 2D Hemin-MOF sheets, this composite can serve as the peroxidase mimics and PtNPs can act as an anchor to capture the antibody. Therefore, this hybrid nanosheet-modified electrode is used as an electrochemical sensing platform for ultrasensitive pig immunoglobulin G (IgG) and the surface-protective antigen (Spa) protein of Erysipelothrix rhusiopathiae immunodetection. Moreover, this work provides a new avenue for the electrochemical synthesis of 2D/3D MOF hybrid nanocomposites with a high surface area and biomimetic catalysts.

High-Temperature and Large-Polarization Ferroelectric with Second Harmonic Generation Response in a Novel Crown Ether Clathrate

Molecular ferroelectrics of high-temperature reversible phase transitions are very rare and have attracted increasing attention in recent years. In this paper is described the successful synthesis of a novel high-temperature host-guest inclusion ferroelectric: [(C₆ H₅ NF₃ )(18-crown-6)][BF₄ ] (1) that shows a pair of reversible peaks at 348 K (heating) and 331 K (cooling) with a heat hysteresis about 17 K by differential scanning calorimetry measurements, thus indicating that 1 undergoes a reversible structural phase transition. Variable-temperature PXRD and temperature-dependent dielectric measurements further prove the phase-transition behavior of 1. The second harmonic response demonstrates that 1 belongs to a non-centrosymmetric space group at room temperature and is a good nonlinear optical material. In its semiconducting properties, 1 shows a wide optical band gap of about 4.43 eV that comes chiefly from the C, H and O atoms of the crystals. In particular, the ferroelectric measurements of 1 exhibit a typical polarization-electric hysteresis loop with a large spontaneous polarization (P_s ) of about 4.06 μC/cm² . This finding offers an alternative pathway for designing new ferroelectric-dielectric and nonlinear optical materials and related physical properties in organic-inorganic and other hybrid crystals.

The First High-Temperature Supramolecular Radical Ferroics

Organic radical ferroics such as TEMPO have attracted widespread interest. However, the relatively low Curie temperature of 287 K and melting point of 311 K severely hinder its application potential. Despite extensive interest, high-temperature radical ferroics have not yet been found. Here, taking advantage of chemical design and supramolecular radical chemistry, we designed two high-temperature organic supramolecular radical ferroics [(NH₃ -TEMPO)([18]crown-6)](ReO₄ ) (1) and [(NH₃ -TEMPO)([18]crown-6)](ClO₄ ) (2), which can retain ferroelectricity up to 413 K and 450 K, respectively. To our knowledge, they are both the first supramolecular radical ferroics and unprecedented high-temperature radical ferroics, where the supramolecular component is vital for the stabilization of the radical and extending the working temperature window. Both also have paramagnetism, non-interacting spin moments, and excellent piezoelectric and electrostrictive behaviors comparable to that of LiNbO₃ .

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.