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The perovskite structure accommodates many different combinations of elements, making it attractive for use in a wide variety of applications. Building perovskites out of only organic compounds is appealing because these materials tend to be flexible, fracture-resistant, and potentially easier to synthesize than their inorganic counterparts. Ye et al. describe a previously unknown family of all-organic perovskites, of which they synthesized 23 different family members (see the Perspective by Li and Ji). The compounds are attractive as ferroelectrics, including one compound with properties close to the well-known inorganic ferroelectric BaTiO 3 . Science , this issue p. 151 ; see also p. 132 A family of all-organic perovskites has attractive ferroelectric properties. Inorganic perovskite ferroelectrics are widely used in nonvolatile memory elements, capacitors, and sensors because of their excellent ferroelectric and other properties. Organic ferroelectrics are desirable for their mechanical flexibility, low weight, environmentally friendly processing, and low processing temperatures. Although almost a century has passed since the first ferroelectric, Rochelle salt, was discovered, examples of highly desirable organic perovskite ferroelectrics are lacking. We found a family of metal-free organic perovskite ferroelectrics with the characteristic three-dimensional structure, among which MDABCO ( N -methyl- N' -diazabicyclo[2.2.2]octonium)–ammonium triiodide has a spontaneous polarization of 22 microcoulombs per square centimeter [close to that of barium titanate (BTO)], a high phase transition temperature of 448 kelvins (above that of BTO), and eight possible polarization directions. These attributes make it attractive for use in flexible devices, soft robotics, biomedical devices, and other applications.

Piezoelectric materials allow conversion between electricity and mechanical stresses. The most efficient piezoelectric materials are ceramics such as BaTiO 3 or PbZrO 3 , which are also extremely stiff. You et al. identified an organic perovskite structured piezoelectric material that is far more pliable yet has a piezoelectric response similar to that of traditional ceramics. This material may be a better option to use as a mechanical sensor for flexible devices, soft robotics, biomedical devices, and other micromechanical applications that benefit from a less stiff piezoelectric material. Science , this issue p. 306 Trimethylchloromethyl ammonium trichloromanganese(II) may be a flexible material competitive for piezoelectric applications. Molecular piezoelectrics are highly desirable for their easy and environment-friendly processing, light weight, low processing temperature, and mechanical flexibility. However, although 136 years have passed since the discovery in 1880 of the piezoelectric effect, molecular piezoelectrics with a piezoelectric coefficient d 33 comparable with piezoceramics such as barium titanate (BTO; ~190 picocoulombs per newton) have not been found. We show that trimethylchloromethyl ammonium trichloromanganese(II), an organic-inorganic perovskite ferroelectric crystal processed from aqueous solution, has a large d 33 of 185 picocoulombs per newton and a high phase-transition temperature of 406 kelvin (K) (16 K above that of BTO). This makes it a competitive candidate for medical, micromechanical, and biomechanical applications.

Inorganic semiconductor ferroelectrics such as BiFeO 3 have shown great potential in photovoltaic and other applications. Currently, semiconducting properties and the corresponding application in optoelectronic devices of hybrid organo-plumbate or stannate are a hot topic of academic research; more and more of such hybrids have been synthesized. Structurally, these hybrids are suitable for exploration of ferroelectricity. Therefore, the design of molecular ferroelectric semiconductors based on these hybrids provides a possibility to obtain new or high-performance semiconductor ferroelectrics. Here we investigated Pb-layered perovskites, and found the layer perovskite (benzylammonium) 2 PbCl 4 is ferroelectric with semiconducting behaviours. It has a larger ferroelectric spontaneous polarization P s =13 μC cm −2 and a higher Curie temperature T c =438 K with a band gap of 3.65 eV. This finding throws light on the new properties of the hybrid organo-plumbate or stannate compounds and provides a new way to develop new semiconductor ferroelectrics. Lead-halide perovskite compounds have seen a considerable interest for their optoelectronic properties. Here, the authors discover a ferroelectric halide perovskite compound as an alternative pathway towards designing semiconductor ferroelectrics.

Molecular ferroelectrics are currently an active research topic in the field of ferroelectric materials. As complements or alternatives of conventional inorganic ferroelectrics, they have been designed to realize various novel properties, ranging from multiferroicity and semiconductive ferroelectricity to ferroelectric photovoltaics and ferroelectric luminescence. The stabilizing of ferroelectricity in various systems is owing to the flexible tailorability of the organic components. Here we describe the construction of optically active molecular ferroelectrics by introducing homochiral molecules as polar groups. We find that the ferroelectricity in ( R )-(−)-3-hydroxlyquinuclidinium halides is due to the alignment of the homochiral molecules. We observe that both the specific optical rotation and rotatory direction change upon paraelectric-ferroelectric phase transitions, due to the existence of two origins from the molecular chirality and spatial arrangement, whose contributions vary upon the transitions. The optical rotation switching effect may find applications in electro-optical elements. Ferroelectric phase transitions are normally accompanied by structural changes in the materials. Here, Li et al . synthesize homochiral molecular crystals and utilize their ferroelectric transitions to achieve optical switches with different refractive indices for left- and right-handed polarizations.

Noncollinear dipole textures greatly extend the scientific merits and application perspective of ferroic materials. In fact, noncollinear spin textures have been well recognized as one of the core issues of condensed matter, e.g. cycloidal/conical magnets with multiferroicity and magnetic skyrmions with topological properties. However, the counterparts in electrical polarized materials are less studied and thus urgently needed, since electric dipoles are usually aligned collinearly in most ferroelectrics/antiferroelectrics. Molecular crystals with electric dipoles provide a rich ore to explore the noncollinear polarity. Here we report an organic salt (H 2 Dabco)BrClO 4 (H 2 Dabco = N , N ’−1,4-diazabicyclo[2.2.2]octonium) that shows a transition between the ferroelectric and antiferroelectric phases. Based on experimental characterizations and ab initio calculations, it is found that its electric dipoles present nontrivial noncollinear textures with 60 o -twisting angle between the neighbors. Then the ferroelectric-antiferroelectric transition can be understood as the coding of twisting angle sequence. Our study reveals the unique science of noncollinear electric polarity. The authors find that the electric dipoles of a hybrid molecular material exhibit two kinds of intrinsic noncollinear textures, corresponding to its ferroelectric and antiferroelectric states.

Ferroelectric thin-films are highly desirable for their applications on energy conversion, data storage and so on. Molecular ferroelectrics had been expected to be a better candidate compared to conventional ferroelectric ceramics, due to its simple and low-cost film-processability. However, most molecular ferroelectrics are mono-polar-axial, and the polar axes of the entire thin-film must be well oriented to a specific direction to realize the macroscopic ferroelectricity. To align the polar axes, an orientation-controlled single-crystalline thin-film growth method must be employed, which is complicated, high-cost and is extremely substrate-dependent. In this work, we discover a new molecular ferroelectric of quinuclidinium periodate, which possesses six-fold rotational polar axes. The multi-axes nature allows the thin-film of quinuclidinium periodate to be simply prepared on various substrates including flexible polymer, transparent glasses and amorphous metal plates, without considering the crystallinity and crystal orientation. With those benefits and excellent ferroelectric properties, quinuclidinium periodate shows great potential in applications like wearable devices, flexible materials, bio-machines and so on. Molecular ferroelectric crystals hold promise in data storage applications, yet their preparations by maximizing molecular polarization are challenging. Here, You et al . report quinuclidinium periodate with six rotation axes and grow them in macroscopic ferroelectric thin films via a solution process.

Sliding ferroelectricity is a recently observed polarity existing in two-dimensional materials. However, due to the weak polarization and poor electrical insulation in these materials, existing experimental evidences are indirect and mostly based on nanoscale transport properties or piezoresponse force microscopy. We report the direct observation of sliding ferroelectricity, using a high-quality amphidynamic single crystal (15-crown-5)Cd 3 Cl 6 , which possesses a large bandgap and so allows direct measurement of polarization–electric field hysteresis. This coordination polymer is a van der Waals material, which is composed of inorganic stators and organic rotators as determined by X-ray diffraction and NMR characterization. From density functional theory calculations, we find that after freezing the rotators, an electric dipole is generated in each layer driven by the geometric mechanism, while a comparable ferroelectric polarization originates from the interlayer sliding. The net polarization of these two components can be directly measured and manipulated. Our finding provides insight into low-dimensional ferroelectrics, especially control of the synchronous dynamics of rotating molecules and sliding layers in solids. Two-dimensional materials can present ferroelectricity by layer sliding, but electrical confirmation is lacking due to narrow bandgaps. Here, a single-crystal coordination polymer with large bandgap enabling direct electrical measurement of P – E hysteresis is shown to present sliding ferroelectricity.

Magnet‐optical materials embracing coupled magnetic and photoluminescent properties in single phase are promising in microelectronics and optoelectronic devices. However, the current research mainly focuses on traditional inorganic materials, and there are few reports on molecule materials. Recently, we synthesized an organic–inorganic hybrid complex (C6H5C2H3FNH3)2MnCl4 (1) with perovskite structure. Physical measurements show that 1 not only behaves as an antiferromagnet with spin canting but also exhibits unusual fluorescent properties. Importantly, under the magnetic field at different temperatures, the luminous intensity of 1 changed, and a red‐shift occurred with obviously optical hysteresis. These phenomena directly prove the existence of magneto‐optical coupling in 1. More interestingly, the optical hysteresis can be observed in both low and high field, which is unprecedented in other molecular materials. Even in traditional inorganic materials, it can only be observed in strong field. This special function provides the possibility for the application of low energy consumption optoelectronic devices. This is the first coordination complex showing magneto‐luminescence. Besides, under different temperatures and applied magnetic fields, the title complex exhibits the unusual magneto‐fluorescence properties, in which the emission peak has an obvious red‐shift with the increasing magnetic field with a hysteresis loop even in low field. This special phenomenon provides the possibility for the application of low energy consumption optoelectronic devices.

Halide perovskites have shown promising potential for direct X-ray detection due to their high X-ray absorption coefficient, low trap states and convenient fabrication process. However, it is still a challenge to achieve high sensitivity, low dark current and low detection limit in a single material. The deep reason for this is the trade-off between the material’s μτ product and resistivity. Here we report the construction of an organic–inorganic hybrid anti-perovskite ((2-Habch) 3 Cl(PtI 6 )) with indirect transition and low orbital symmetry at the band edge to achieve an ultralong intrinsic lifetime and thus break the trade-off. (2-Habch) 3 Cl(PtI 6 ) achieves an unprecedented long carrier lifetime of >3 ms, leading to a large μτ product of 6.25 × 10 −3  cm 2  V −1 and high resistivity of 10 12  Ω cm, outperforming most X-ray detection materials. These properties enabled the development of X-ray detectors that simultaneously achieve an ultralow dark current of 0.21 nA cm −2 , high sensitivity of 1.0 × 10 4  µC Gy air −1  cm −2 , ultralow detection limit of 2.4 nGy air  s −1 and excellent operational stability with no observable baseline drift, outperforming state-of-the-art perovskite single-crystal detectors. The rare combination of high performance in almost every figure of merit in the anti-perovskite-based X-ray detector could enable new-generation X-ray detection systems. The researchers synthesize organic–inorganic hybrid inverse perovskites that exhibit excellent carrier lifetime and mobility–lifetime product and high resistivity, enabling stable X-ray detectors with performance arguably outperforming state-of-the-art perovskite single-crystal detectors.

Stimuli-responsive materials with coexisting nonlinear optical (NLO) and dielectric properties are technologically important, which enable simultaneous conversion of optoelectronic properties between different states under external stimuli. By rationally screening guest cations (C6H5NF2)+ in the crown-ether inclusion system, we synthesized a crown-ether supramolecular compound [(C6H5NF2)(18-crown-6)][PF6] (1). Differential scanning calorimetry (DSC) showed that 1 undergoes a reversible phase transition above room temperatures (305 K/292 K), with a thermal hysteresis of 13 K. Temperature-dependent dielectric and NLO measurements show that the compound exhibits two distinct switching response behaviors. Structural analysis indicates that the order–disorder change of the host molecule 18-crown-6 and the guest organic cation during the phase transition induces the dielectric and NLO switching behavior of the compound.