Molecular ferroelectric pyridin-2-ylmethanaminium perchlorate with phase transition induced by disorder of perchlorate

Increasing the ferroelastic phase transition temperature of hybrid perovskites through a mixed phosphonium and ammonium cation strategy

[(CH₃)₃PCH₂CH₂CH₃]₂(n-C₄H₉NH₃)Bi₂Br₉ (1) was obtained by a mixed organic cation strategy. The introduction of phosphonium cations increases the potential energy barrier for the motion of cations, which raises the ferroelastic phase transition temperature of 1 above room temperature, unlike the low-temperature ferroelasticity of [n-C₄H₉NH₃]₂[BiBr₅]. This provides a new idea for exploring and designing molecular ferroelastic materials with excellent performance.

New Low-Dimensional Lead-Free Perovskite (2-AMP)2BiX7·H2O (X = Cl, Br) Crystals: Synthesis, Stability, and Nonlinear Optical Properties

Organic-inorganic hybrid Pb-halide perovskites have attracted tremendous interest due to their potential application in photovoltaic and optoelectronic fields. However, the toxicity and poor stability of Pb-halide perovskites have become key bottlenecks toward their future commercialization and industrialization. Therefore, in this work, two novel hybrid lead-free perovskite nonlinear optical (NLO) crystals (2-AMP)₂BiX₇·H₂O (X = Cl, Br) with high stability were successfully synthesized. Both the crystals belong to the orthorhombic P2₁2₁2₁ space group, displaying a zero-dimensional perovskite structure. The thermal, environmental, and solvent atmospheric stabilities were comprehensively investigated, with high thermal stability up to 170 °C and high environmental and high solvent atmospheric stability observed for (2-AMP)₂BiBr₇·H₂O. First-principles calculations were carried out to study the relationship of the structure and properties. A large birefringence of 0.1368@1064 nm was determined for (2-AMP)₂BiBr₇·H₂O, which was derived from the strong aeolotropic conjugated π-electron distribution of planar 2-aminomethylpyridium. A second-harmonic generation (SHG) effect that was 0.25 and 0.32 times that of KH₂PO₄ (KDP) was measured for (2-AMP)₂BiCl₇·H₂O and (2-AMP)₂BiBr₇·H₂O, respectively, and the stronger SHG response of bromide was attributed to the larger distortions of {BiBr₆} octahedrons. This work may offer new guidance for exploration of low toxicity and high stability of perovskite NLO 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.

Para–ferroelectric phase transition induces an excellent second harmonic generation response and a prominent switchable dielectric constant change based on a metal-free ionic crystal

A novel metal-free compound, [H₂(bpyp)][ClO₄]₂, undergoes a ferroelectric to paraelectric reversible phase transition at T_c, with excellent NLO response, prominent dielectric constant change, moderate ferroelectric polarization, and wide bandgap.

Properties and growth of large single crystals of one-dimensional organic lead iodine perovskite

Here, we demonstrate for the first time the growth of 2 mm × 4 mm × 8 mm sized single crystal one dimensional organic lead iodine perovskite – DMAPbI₃ ((CH₃)₂NH₂PbI₃).

H/F substituted perovskite compounds with above-room-temperature ferroelasticity: [(CH3)4P][Cd(SCN)3] and [(CH3)3PCH2F][Cd(SCN)3]

An organic-inorganic perovskite compound [(CH₃)₄P][Cd(SCN)₃] (1) and its fluorine-substituted product [(CH₃)₃PCH₂F][Cd(SCN)₃] (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.