Enhancing Short-Range Interactions to Broaden the Temperature Range for Coexistence of Antiferroelectricity and Ferroelasticity.

Antiferroelectric (AFE) materials, characterized by double electric hysteresis loops, can be transformed to the ferroelectric (FE) phase under an external electric field, making them promising candidates for electronic energy storage and solid-state refrigeration. Additionally, the field-induced strain in AFE materials is contingent upon the direction of the electric field, rendering it with a switching characteristic. Although AFE materials have made progress in the field of energy storage and negative electrocaloric effect, the coexistence of AFE and ferroelasticity is still rarely reported.

Dehydration Induced a Structural Transformation into a One-Dimensional Hybrid Perovskite with Second Harmonic Generation and Dual Dielectric Switching.

Hybrid organic-inorganic perovskites with structural transformation have garnered continued interest in recent years for their potential as multifunctional materials in the field of optoelectronics and smart devices. Herein, we report a novel hybrid organic-inorganic halide, [CNOH][CdCl(HO)] (). Remarkably, the centrosymmetric compound undergoes a structural transformation to a novel noncentrosymmetric hybrid perovskite [CNOH][CdCl] () after dehydration.

Templating Influence of Regulated Inorganic Framework in Two-Dimensional Ferroelastic Perovskites: (C H CH NH ) [MCl ] (M=Mn and Cd).

The remarkable material stability and structural diversity of two-dimensional (2D) organic-inorganic hybrid perovskites (OIHPs) constitute a vast available library of versatile materials. In particular, ferroelastic property, for which the spontaneous strain can be transformed by applying mechanical stress, is very promising for extensive nanotechnological applications. However, integrating ferroelastic property into 2D OIHPs is still in its infancy.

Two-step nonlinear optical switch in a hydrogen-bonded perovskite-type crystal.

Switchable nonlinear optical (NLO) materials have aroused broad interest on account of their captivating optical and electronic properties. We demonstrate a novel perovskite-type crystal with exceptional hydrogen bond interactions that are associated with the onset of reorientational motions of organic cations and thus induce the occurrence of two successive phase transitions to be a two-step NLO switch. This finding affords an alternative approach for the design and assembly of switchable NLO materials.

(CHN)PbI: A 2D Hybrid Perovskite Solid-State Phase Transition Material with Semiconducting Properties.

Two-dimensional organic-inorganic hybrid perovskites (OIHPs) have gained attention as a result of their flexibility and adjustability of the structure. However, the large band gap of two-dimensional perovskites limits their application in the photoelectric field. In the present work, we report a two-dimensional organic-inorganic hybrid compound of (CHN)PbI () with a narrow band gap, which consists of [PbI] layers and -(2-aminoethyl)piperidinium cations.

Successive Phase Transitions and Dual Dielectric Switching in an Organic-Inorganic Hybrid Perovskite.

Molecular phase transition compounds have become a hot research area in recent years because of their potential as functional materials, such as ferroelectrics, ferroelastics, dielectric switches, etc. However, materials combining switchable dielectric properties and ferroelasticity are still rare. Here, we reported an organic-inorganic hybrid perovskite, [CPtmp][Cd(SCN)] () ([CPtmp] is a cyclopentyltrimethylphosphonium cation), with a potential ferroelastic property.

Phosphonium-Based One-Dimensional Perovskite with Switchable Dielectric Behaviors and Phase Transitions.

The one-dimensional (1D) ABX-type perovskite [(CH)PCHF]CdClBr () has been obtained on the basis of the design of an organic-inorganic hybrid. Strikingly, it experiences sequential phase transitions at around 295 and 336 K, respectively. Given the noticeable steplike dielectric anomalies in the vicinity of 295 K, is identified as a promising dielectric-switchable material.

A one-dimensional switchable dielectric material with Pd uptake function: [(CH)NHS]BiCl.

A semiconductor material [(CH)NHS]BiCl (1) exhibits dielectric switching and Pd uptake functions. The thioether group in 1 provides an opportunity for Pd uptake. After 1 adsorbs Pd, the dielectric switching disappears, so that Pd adsorption can be monitored by dielectric measurements.

A Three-Dimensional Molecular Perovskite Ferroelastic with Two-Step Switching of Quadratic Nonlinear Optical Properties Tuned by Molecular Chiral Design.

Molecular perovskite materials have recently attracted extraordinary interest from the academic community owing to their excellent multifunctional properties. Nevertheless, although massive efforts have been made, molecular ferroelastics with three-dimensional (3D) perovskite structures are still rare. Herein, we report two 3D organic-inorganic hybrid perovskites [(2-hydroxy-propyl)-tripropyl-ammonium][Mn(dca)] () and [(2-hydroxy-1-methyl-ethyl)-tripropyl-ammonium] [Mn(dca)] () [dca = dicyanamide, N(CN)].

Phase Transition and Band Gap Regulation by Halogen Substituents on the Organic Cation in Organic-Inorganic Hybrid Perovskite Semiconductors.

In the last decade, hybrid materials have received widespread attention. In particular, hybrid lead halide perovskite-type semiconductors are very attractive owing to their great flexibility in band gap engineering. Here, by using precise molecular modifications, three one-dimensional perovskite-type semiconductor materials are designed and obtained: [Me PCH X][PbBr ] (X=H, F, and Cl for compounds 1, 2, and 3, respectively).

Unique Design Strategy for Dual Phase Transition That Successfully Validates Dual Switch Implementation in the Dielectric Material.

Dual phase transition/switch materials are a critical cornerstone of information storage and sensing. However, they are difficult to design successfully, and compared with materials showing single-switchable phase transitions, the dual ones retain many challenges by far. Therefore, the significance of a general strategy is far greater than an accidental success.

Three-Dimensional Metal-Free Molecular Perovskite with a Thermally Induced Switchable Dielectric Response.

Temperature-responsive materials with switching physical properties have been widely researched. Among them, the switchable dielectric perovskite materials show potential applications in the electrical and electronic industries and even the intelligence industries. However, perovskite oxides and hybrid organic-inorganic perovskites, as the most representative switchable dielectric materials, are limited by bad biocompatibility.

Two-Dimensional Organic-Inorganic Perovskite Ferroelectric Semiconductors with Fluorinated Aromatic Spacers.

Two-dimensional (2D) organic-inorganic perovskites (OIPs), with improved material stability over their 3D counterparts, are highly desirable for device applications. It is their considerable structural diversity that offers an unprecedented opportunity to engineer materials with fine-tuning functionalities. The isosteric substitution of hydrogen by an electronegative fluorine atom has been proposed as a useful route to improve the photovoltaic performance of 2D OIPs, whereas its valuable role in developing ferroelectricity is still waiting for further exploration.

Anion-Regulated Molecular Rotor Crystal: The First Case of a Stator-Rotator Double Switch with Relaxation Behavior.

Molecular rotational motion is crucial in artificial molecular machines and is expected to be very significant for the development of an electronic information molecular machine as mentioned in the 2016 Nobel Prize. However, controlling multiple motor modes is a huge challenge. Here, we report a case in which the structural phase transition effectively triggers multiple motor modes by regulating the rotational speed of the cation and/or anion.

H/F substituted perovskite compounds with above-room-temperature ferroelasticity: [(CH)P][Cd(SCN)] and [(CH)PCHF][Cd(SCN)].

An organic-inorganic perovskite compound [(CH)P][Cd(SCN)] (1) and its fluorine-substituted product [(CH)PCHF][Cd(SCN)] (2) exhibit ferroelastic phase transitions above room temperature. The very close van der Waals radii of H and F atoms ensure isomorphism of the crystal structures. However, the higher phase transition temperature, stronger ferroelastic spontaneous strain value and dielectric properties of 2 can possibly be explained by differences in the electronegativity between F and H atoms.

Toward the Targeted Design of Molecular Ferroelectrics: Modifying Molecular Symmetries and Homochirality.

Although the first ferroelectric discovered in 1920 is Rochelle salt, a typical molecular ferroelectric, the front-runners that have been extensively studied and widely used in diverse applications, such as memory elements, capacitors, sensors, and actuators, are inorganic ferroelectrics with excellent electrical, mechanical, and optical properties. With the increased concerns about the environment, energy, and cost, molecular ferroelectrics are becoming promising supplements for inorganic ferroelectrics. The unique advantages of high structural tunability and homochirality, which are unavailable in their inorganic counterparts, make molecular systems a good platform for manipulating ferroelectricity.

3D Organic-Inorganic Perovskite Ferroelastic Materials with Two Ferroelastic Phases: [Et P(CH ) F][Mn(dca) ] and [Et P(CH ) Cl][Mn(dca) ].

Organic-inorganic hybrid perovskite-type multiferroics have attracted considerable research interest owing to their fundamental scientific significance and promising technological applications in sensors and multiple-state memories. The recent achievements with divalent metal dicyanamide compounds revealed such malleable frameworks as a unique platform for developing novel functional materials. Herein, two 3D organic-inorganic hybrid perovskites [Et P(CH ) F][Mn(dca) ] (1) and [Et P(CH ) Cl][Mn(dca) ] (2) (dca=dicyanamide, N(CN) ) are presented.

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 [(CH)NCHCl]MnCl, this cation rotation pattern with a motor-type motion structure has continued to attract our attention.

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.

Fluorine Substitution Induced High T of Enantiomeric Perovskite Ferroelectrics: ( R) - and ( S) -3-(Fluoropyrrolidinium)MnCl.

The past decade has witnessed much progress in designing molecular ferroelectrics, whose intrinsic mechanical flexibility, structural tunability, and easy processability are desirable for next-generation flexible and wearable electronic devices. However, an obstacle in expanding their promising applications in nonvolatile memory elements, capacitors, and sensors is effectively modulating the Curie temperature ( T). Here, taking advantage of fluorine substitution on the reported molecular ferroelectric, (pyrrolidinium)MnCl, we present enantiomeric perovskite ferroelectrics, namely, ( R) - and ( S) -3-(fluoropyrrolidinium)MnCl.

Halogen substitution effects on optical and electrical properties in 3D molecular perovskites.

Both 3D organic-inorganic perovskites ([Et3P(CH2)2Cl][Cd(dca)3] (1) and [Et3P(CH2)2F][Cd(dca)3] (2) [dca = dicyanamide, N(CN)2-]) display two sequentially reversible high-temperature phase transitions and switchable dielectric properties. Through halogen substitution, 1 shows exceptional switching behaviour of second harmonic generation effects and remarkably 2 represents the first above-room-temperature 3D ferroelastic material characterized by two ferroelastic phases.

Molecular design of high-temperature organic dielectric switches.

A design strategy of reducing the molecular symmetry was used to obtain a series of picrate-based high-temperature phase transition compounds. Their dielectric switching behaviours accompanied by phase transitions can be attributed to the order-disorder transitions of the cations and the displacements of both cations and anions.

A Room-Temperature Hybrid Lead Iodide Perovskite Ferroelectric.

Organic-inorganic hybrid perovskite, [CHNH]PbI, holds a great potential for next-generation solar devices. However, whether the ferroelectricity exists in [CHNH]PbI and results in the ultrahigh performance is not at present clear. Beyond that, no hybrid lead iodide perovskite ferroelectric has yet been found.

Reversible Thermal Dielectric Switch Triggered by Blooming-Flower Structural Phase Transition in Ionic Crystal without Metal.

Due to having excellent properties of sensitive switchable physical and/or chemical response, simple preparation, and environmentally friendly processing, bistable switches (electric switching between "on" and "off" bistable states) have gradually developed into an ideal class of highly smart materials. However, most of them contain metals, especially heavy metals, which are highly toxic to the environment, and metal-free switch materials are rarely reported. Based on this issue, we successfully designed and synthesized organic ion crystals and realized thermal dielectric switching characteristics.

Switchable Dielectric Phase Transition Triggered by Pendulum-Like Motion in an Ionic Co-crystal.

Molecular-based ionic co-crystals, which have the merits of low-cost/easy fabrication processes and flexible structure and functionality, have already exhibited tremendous potential in molecular memory switches and other electric devices. However, dipole (ON/OFF switching) triggering is a huge challenge. Here, we introduce a pendulum-like dynamic strategy to induce the order-disorder transition of a co-crystal [C H N Cl] [Sb Br ] (compound 1).