Strain-Induced Tunable Enhancement of Piezoelectricity in a Novel Molecular Multiferroic Material.

Multiferroics are appealing because of application potentials in data storage devices, sensors, transducers, and energy harvesters. Molecular multiferroics emerge as a promising alternative to inorganic multiferroics due to flexibility, light weight, low toxicity, solution processing, structural diversity, and chemical tunability. While researches have predominantly focused on perovskite structures, studies on molecular ionic multiferroics remain relatively limited.

Organic-Inorganic Hybrid Perovskite for Ferroelectric Catalysis.

Organic-inorganic hybrid perovskite ferroelectric has gained significant attention for its structural flexibility and diversity. They can directly utilize metal nodes and organic groups as active sites in catalysis. Additionally, their ferroelectric polarization occurs around these active sites, significantly enhancing catalytic activity and demonstrating immense potential for applications.

A Melt-Processable Metal Halide Perovskite Ferroelectric.

Molecular ferroelectrics have increasingly garnered significant attention in both fundamental scientific research and technological applications due to their ease of processing, lightweight nature, and mechanical flexibility. Among these, metal halide perovskite ferroelectrics (MHP FEs), a subset of molecule-based ferroelectrics, exhibit diverse functionalities owing to their distinctive structures, thus emerging as a focal point of molecular ferroelectrics research. However, thin films, the predominant application form for MHP FEs, primarily rely on spin-coating, which presents considerable limitations.

Discovery of molecular ferroelectric catalytic annulation for quinolines.

Ferroelectrics as emerging and attractive catalysts have shown tremendous potential for applications including wastewater treatment, hydrogen production, nitrogen fixation, and organic synthesis, etc. In this study, we demonstrate that molecular ferroelectric crystal TMCM-CdCl (TMCM = trimethylchloromethylammonium) with multiaxial ferroelectricity and superior piezoelectricity has an effective catalytic activity on the direct construction of the pharmacologically important substituted quinoline derivatives via one-pot [3 + 2 + 1] annulation of anilines and terminal alkynes by using N,N-dimethylformamide (DMF) as the carbon source. The recrystallized TMCM-CdCl crystals from DMF remain well ferroelectricity and piezoelectricity.

Enhancement of phase transition temperature through hydrogen bond modification in molecular ferroelectrics.

Molecular ferroelectrics are attracting great interest due to their light weight, mechanical flexibility, low cost, ease of processing and environmental friendliness. These advantages make molecular ferroelectrics viable alternatives or supplements to inorganic ceramics and polymer ferroelectrics. It is expected that molecular ferroelectrics with good performance can be fabricated, which in turns calls for effective chemical design strategies in crystal engineering.

Organic-Inorganic Hybrid Perovskite Ferroelectric Nanosheets Synthesized by a Room-Temperature Antisolvent Method.

Over the past years, the application potential of ferroelectric nanomaterials with unique physical properties for modern electronics is highlighted to a large extent. However, it is relatively challenging to fabricate inorganic ferroelectric nanomaterials, which is a process depending on a vacuum atmosphere at high temperatures. As significant complements to inorganic ferroelectric nanomaterials, the nanomaterials of molecular ferroelectrics are rarely reported.

The past 10 years of molecular ferroelectrics: structures, design, and properties.

Ferroelectricity, which has diverse important applications such as memory elements, capacitors, and sensors, was first discovered in a molecular compound, Rochelle salt, in 1920 by Valasek. Owing to their superiorities of lightweight, biocompatibility, structural tunability, mechanical flexibility, , the past decade has witnessed the renaissance of molecular ferroelectrics as promising complementary materials to commercial inorganic ferroelectrics. Thus, on the 100th anniversary of ferroelectricity, it is an opportune time to look into the future, specifically into how to push the boundaries of material design in molecular ferroelectric systems and finally overcome the hurdles to their commercialization.

Rational Design of 2D Metal Halide Perovskites with Low Congruent Melting Temperature and Large Melt-Processable Window.

Metal halide perovskites (MHPs) have garnered significant attention due to their distinctive optical and electronic properties, coupled with excellent processability. However, the thermal characteristics of these materials are often overlooked, which can be harnessed to cater to diverse application scenarios. We showcase the efficacy of lowering the congruent melting temperature () of layered 2D MHPs by employing a strategy that involves the modification of flexible alkylammonium through -methylation and I-substitution.

Wireless Deep Brain Stimulation by Ultrasound-Responsive Molecular Piezoelectric Nanogenerators.

Implantable neural stimulation devices are becoming prevalent in bioelectronic medicine for the precise treatment of various clinical diseases. Nevertheless, the limited lifespan and buckling size of the implanted devices remain significant obstacles for chronic clinical application. In this study, we developed an ultrasound-driven battery-free neurostimulator based on a high-performance mini-sized nanogenerator and demonstrated its successful application for the deep-brain-stimulation (DBS) therapy of Parkinson's disease in a rat model.

First Observation of Negative Capacitance in Molecular Ferroelectric Thin Films.

On the path of persisting Moore's Law, one of the biggest obstacles is the "Boltzmann tyranny," which defines the lower limit of power consumption of individual transistors. Negative capacitance (NC) in ferroelectrics could provide a solution and has garnered significant attention in the fields of nanoelectronics, materials science, and solid-state physics. Molecular ferroelectrics, as an integral part of ferroelectrics, have developed rapidly in terms of both performance and functionality, with their inherent advantages such as easy fabrication, mechanical flexibility, low processing temperature, and structural tunability.

Volume-Confined Fabrication of Large-Scale Single-Crystalline Molecular Ferroelectric Thin Films and Their Applications in 2D Materials.

With outstanding advantages of chemical synthesis, structural diversity, and mechanical flexibility, molecular ferroelectrics have attracted increasing attention, demonstrating themselves as promising candidates for next-generation wearable electronics and flexible devices in the film form. However, it remains a challenge to grow high-quality thin films of molecular ferroelectrics. To address the above issue, a volume-confined method is utilized to achieve ultrasmooth single-crystal molecular ferroelectric thin films at the sub-centimeter scale, with the thickness controlled in the range of 100-1000 nm.

Superior ferroelectricity and nonlinear optical response in a hybrid germanium iodide hexagonal perovskite.

Abundant chemical diversity and structural tunability make organic-inorganic hybrid perovskites (OIHPs) a rich ore for ferroelectrics. However, compared with their inorganic counterparts such as BaTiO, their ferroelectric key properties, including large spontaneous polarization (P), low coercive field (E), and strong second harmonic generation (SHG) response, have long been great challenges, which hinder their commercial applications. Here, a quasi-one-dimensional OIHP DMAGeI (DMA = Dimethylamine) is reported, with notable ferroelectric attributes at room temperature: a large P of 24.

The First Demonstration of Strain-Controlled Periodic Ferroelectric Domains with Superior Piezoelectric Response in Molecular Materials.

Achieving a periodic domain structure in ferroelectric materials to tailor the macroscopic properties or realize new functions has always been a hot topic. However, methods to construct periodic domain structures, such as epitaxial growth, direct writing by scanning tips, and the patterned electrode method, are difficult or inefficient to implement in emerging molecular ferroelectrics, which have the advantages of lightweight, flexibility, biocompatibility, etc. An efficient method for constructing and controlling periodic domain structures is urgently needed to facilitate the development of molecular ferroelectrics in nanoelectronic devices.

Remarkable Enhancement of Piezoelectric Performance by Heavy Halogen Substitution in Hybrid Perovskite Ferroelectrics.

Piezoelectric materials that enable electromechanical conversion have great application value in actuators, transducers, sensors, and energy harvesters. Large piezoelectric () and piezoelectric voltage () coefficients are highly desired and critical to their practical applications. However, obtaining a material with simultaneously large and has long been a huge challenge.

Giant electrocaloric effect in a molecular ceramic.

The electrocaloric effect (ECE) is an efficient and environmentally friendly method for solid-state refrigeration driven by an electric field. However, disregarding the ECE performance, the mass of materials also limits the amount of energy transferred in the cooling process. While molecular ECE materials have been attracting intensive attention with their excellent ECE properties, most reported molecular compounds can only be utilized in the form of thin films or single crystals.

Inch-Size Molecular Ferroelectric Crystal with a Large Electromechanical Coupling Factor on Par with Barium Titanate.

Molecular ferroelectrics with large piezoelectric responses have long been sought for their advantages of light weight, mechanical flexibility, and easy preparation, in contrast to the widely used inorganic counterparts. Representatively, a molecular ferroelectric crystal [MeNCHCl]CdCl (TMCM-CdCl) has been found to show a large piezoelectric coefficient of 220 pC/N exceeding that of BaTiO (You , , 306-309). However, although the of molecular ferroelectrics has achieved great progress, their electromechanical coupling factor , which is essential for various piezoelectric applications, including ultrasonic transducers and actuators, was rarely explored and is far below the level of inorganic ferroelectrics.

Axial-Chiral BINOL Multiferroic Crystals with Coexistence of Ferroelectricity and Ferroelasticity.

Chirality exists everywhere from natural amino acids to particle physics. The introduction of point chirality has recently been shown to be an efficient strategy for the construction of molecular ferroelectrics. In contrast to point chirality, however, axial chirality is rarely used to design ferroelectrics so far.

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.

An Effective Strategy of Introducing Chirality to Achieve Multifunctionality in Rare-Earth Double Perovskite Ferroelectrics.

The hybrid rare-earth double perovskite (HREDP) system provides great convenience for the construction of multifunctional materials. However, suffering from the high symmetry of their intrinsic structure, HREDPs face the challenges in the realization and optimization of ferroelectric and piezoelectric properties. For the first time, after a systematic investigation of the chirality transformation principle, it is found that the introduction of chirality is an efficient strategy for the targeted construction of multifunctionality, which simultaneously increases the possibility of obtaining multiaxial ferroelectricity and ferroelasticity, and effectively realizes a large piezoelectric response.

Molecular Design of Three-Dimensional Metal-Free A(NH)X Perovskites for Photovoltaic Applications.

The intense research activities on the hybrid organic-inorganic perovskites (HOIPs) have led to the greatly improved light absorbers for solar cells with high power conversion efficiency (PCE). However, it is still challenging to find an alternative lead-free perovskite to replace the organohalide lead perovskites to achieve high PCE. This is because both previous experimental and theoretical investigations have shown that the Pb cations play a dominating role in contributing the desirable frontier electronic bands of the HOIPs for light absorbing.

Confinement-Driven Ferroelectricity in a Two-Dimensional Hybrid Lead Iodide Perovskite.

Organic-inorganic hybrid perovskites (OIHPs) hold a great potential for scientific and technological endeavors in the field of ferroelectrics, solar cells, and electroluminescent devices, because of their structural diversity, low cost of manufacture, and ease of fabrication. However, lead iodide perovskite ferroelectrics with narrow band gap have rarely been reported. Here, we present a new two-dimensional (2D) layered lead iodide perovskite ferroelectric, (4,4-DFHHA)PbI (4,4-DFHHA = 4,4-difluorohexahydroazepine), with a spontaneous polarization () of 1.

Bistable State of Protons for Low-Voltage Memories.

Molecular ferroelectrics are attracting tremendous interest because of their easy and environmental-friendly processing, low acoustic impedance, and mechanical flexibility. Their ferroelectric mechanism is mainly ascribed to the order-disorder transition of molecules such as spherical 1,4-diazabicyclo[2.2.

Observation of Vortex Domains in a Two-Dimensional Lead Iodide Perovskite Ferroelectric.

Topological defects, such as vortices and skyrmions, provide a wealth of splendid possibilities for new nanoscale devices because of their marvelous electronic, magnetic, and mechanical behaviors. Recently, great advances have been made in the study of the ferroelectric vortex in conventional perovskite oxides, such as BaTiO and BiFeO. Despite extensive interest, however, no intriguing ferroelectric vortex structures have yet been found in organic-inorganic hybrid perovskites (OIHPs), which are desirable for their mechanical flexibility, ease of fabrication, and low acoustical impedance.