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Out‐of‐plane polarization is a highly desired property of two‐dimensional (2D) ferroelectrics for application in vertical sandwich‐type photoferroelectric devices, especially in ultrathin ferroelectronic devices. Nevertheless, despite great advances that have been made in recent years, out‐of‐plane polarization remains unrealized in the 2D hybrid double perovskite ferroelectric family. Here, from our previous work 2D hybrid double perovskite HQERN ((S3HQ)4EuRb(NO3)8, S3HQ=S‐3‐hydroxylquinuclidinium), we designed a molecular strategy of F‐substitution on organic component to successfully obtain FQERN ((S3FQ)4EuRb(NO3)8, S3FQ=S‐3‐fluoroquinuclidinium) showing circularly polarized luminescence (CPL) response. Remarkably, compared to the monopolar axis ferroelectric HQERN, FQERN not only shows multiferroicity with the coexistence of multipolar axis ferroelectricity and ferroelasticity but also realizes out‐of‐plane ferroelectric polarization and a dramatic enhancement of Curie temperature of 94 K. This is mainly due to the introduction of F‐substituted organic cations, which leads to a change in orientation and a reduction in crystal lattice void occupancy. Our study demonstrates that F‐substitution is an efficient strategy to realize and optimize ferroelectric functional characteristics, giving more possibility of 2D ferroelectric materials for applications in micro‐nano optoelectronic devices. [ABSTRACT FROM AUTHOR]

A series of RbEu bimetallic ammonium metal nitrate hybrid analogues, [(CH3)3NCH2X]2[RbEu(NO3)6] (X = Cl, 1; Br, 2; I, 3), have been synthesized via solvent evaporation. This series shows similar cage-like perovskite frameworks, in which the cations are confined in the spaces enclosed by the hydrogen-bonding interactions. They display structural phase transitions between 200–430 K. Detailed single-crystal structural analysis of 1–3 reveals the change of the dynamics of the cation and the distortion of the [Rb4Eu4(NO3)12] anionic framework is the driving force for the structural phase transition. Meanwhile, the thermal and dielectric anomalies are verified by differential scanning calorimetry and dielectric measurements, respectively. Interestingly, the subtle change of cation significantly affects the switching temperature and dielectric behaviors, showing the typical 'butterfly effect' in these RbEu bimetallic hybrids. Notably, they also display excellent optical properties, that is, the Eu3+ ion acts as the activator of the photoluminescence property. Meanwhile, compounds 1–3 have phosphorescent characteristics and 1 has the highest fluorescence quantum yield (FQY) of 57.82%. This finding will be evidently meaningful for exploring high-performance multifunctional switching materials for novel applications. [ABSTRACT FROM AUTHOR]

All crystals are not ideal, and many of their properties are often determined not by the regular arrangement of atoms, but by the irregular arrangement of crystal defects. Many properties of materials can be controlled effectively by proper use of solid defects. By substitution of NH4+ ion of a hexagonal perovskite structure (H2dabco)(NH4)(NO3)3 (dabco=1,4‐diazabicyclo[2.2.2]octane, 1) with Cd2+ ion, we obtained a new metal‐vacancy compound (H2dabco)2Cd(H2O)2(NO3)6 (2). It exhibits a ferroelectric‐paraelectric phase transition at 261 K. A comparison of the various‐temperature single‐crystal structures indicates that the coordination twist of Cd2+ ion leads to instability of the lattices and excellent ferroelectricity. These findings reveal that the vacancy can be utilized as an element to produce ferroelectricity and may start the chemistry of metal‐vacancy coordination compounds. These findings reveals that the vacancy can be utilized as an effective means to tune the symmetry and produce ferroelectricity. [ABSTRACT FROM AUTHOR]

Copper (I) based halide scintillators have received high attention due to their high light yield. At the same time, researchers are increasingly interested in exploring organic‐inorganic hybrid copper(I) based halides, due to the diversity and tunability of structures. Here, we describe high‐efficiency photoluminescence and X‐ray excited luminescence in (DFPD)3Cu2I5 (1) (DFPD=4,4‐difluoro‐bipiperidinium). 1 is comprised of a unique [Cu2I5]3− cluster, which have typical structure allowing high‐transition‐probability self‐trapped exciton emission (one Cu+ ion adopts the tetrahedral coordination geometry, the other trigonal planar coordination geometry, the Cu−Cu distance (2.574 Å) is short). Accordingly, 1 shows efficient yellow‐green photoluminescence with the maximum at 527 nm, a full‐width at half‐maximum of 99.2 nm, a large Stokes shift of 214 nm (1.6 eV) and a quantum yield of 77.15 %. Polycrystalline 1 can also convert high‐energy X‐ray photons into UV‐visible pulsed fluorescence with the light yield of 5000 photons/MeV. This finding plays a valuable role in the development of organic‐inorganic hybrid copper(I) based scintillators. [ABSTRACT FROM AUTHOR]

Organic–inorganic hybrid molecular ferroelectrics have attracted broad attention in the field of research of ferroelectric materials. Following the surge of stable candidates, hybrid bimetal molecular-based materials have been recently explored to achieve excellent ferroelectricity. However, rare hybrid bimetal molecular ferroelectrics were reported. Inspired by "ferroelectrochemistry", a chiral nitrite-based hybrid bimetal molecular ferroelectric material, [(R)-3-quinuclidinol]2[LiCo(NO2)6] (1), was reported. The ferroelectric-paraelectric phase transition (C2 ↔ P321) behaviour of 1; was found at 343 K (Curie temperature, Tc) with a spontaneous electronic polarization (Ps) of 0.52 μC cm−2 and a coercive field (Ec) of 48 kV cm−1 at 298 K. Various-temperature single crystal structural analysis and dielectric constant measurements reveal that the rapid rotation of the organic cation and slight order–disorder transition of the NO2− anion are the origin of the ferroelectricity. To our knowledge, 1 is the first example of a nitrite-based hybrid bimetal molecular ferroelectric material that is triggered by an external electric field. This finding establishes a clear stimulus–structure–response relationship in advanced hybrid ferroelectric materials. [ABSTRACT FROM AUTHOR]

As a mechanical analog of ferroelectricity and ferromagnetism, ferroelasticity has made outstanding contributions in the fields of energy conversion, information processing, and mechanical switching. However, research on 2D ferroelasticity is lacking so far, and it is still a challenge to synthesize 2D perovskite ferroelastics. Here, we successfully constructed three 2D organic–inorganic hybrid ferroelastics: (PEA)2CdCl4 [PEA = phenethylamium cation, 1], (3-FPEA)2CdCl4 [3-FPEA = 3-fluorophenethylamium cation, 2] and (4-FPEA)2CdCl4 [4-FPEA = 4-fluorophenethylamium cation, 3]. These compounds undergo a structural phase transition between 379–385 K, exhibit temperature-triggered ferroelasticity, and possess a dielectric transition. The structural analysis of temperature-variable single crystals indicates that the reason for the phase transition of the ferroelastics is the order–disorder transition of cations and distortion of the anion framework. This research provides new options for a new generation of 2D perovskite ferroelastics. [ABSTRACT FROM AUTHOR]

Molecule-based switchable dielectrics with distinct changes of dielectric constant, which enable conversion of electronic properties between different states under external stimuli, are technologically important. The crown-ether clathrate system is a highly promising class of molecule-based switchable dielectrics. Herein, by choosing yttrium nitrate to be assembled with a 15-crown-5 molecule, we synthesized a new crown-ether clathrate, namely [15-crown-5][Y(NO3)2(H2O)5][NO3] (1). One relatively small thermal anomaly peak was observed centered at 230 K (Ttr) for compound 1. Single-crystal structures obtained at various temperatures revealed its reversible phase transition to be driven by the synergistic effect of the dynamic changes of the counter [NO3]− anions from an ordered to disordered state and the relatively strong thermal vibrations of the 15-crown-5 molecules, along with the rearrangement of [Y(NO3)2(H2O)5]+ cations in the crystal. Meanwhile, compound 1 also displayed a bistable dielectric response characteristically found in different structural phases. This discovery confirmed the possibility of using compound 1 as a molecule-based dielectric switching material. [ABSTRACT FROM AUTHOR]