A polar oxyhalogen-vanadate compound (C5NH13Cl)2VOCl4 with optical and two-staged dielectric switch behavior

Polar organic-inorganic hybrid materials have been applied in ferroelectricity, as well as in devices based on nonlinear optical and piezoelectricity properties. Here, we used a rectangular pyramid structure of [VOCl4]2- to construct a polar compound (C5NH13Cl)2VOCl4 (1). Compound 1 crystallized in the monoclinic P21 space group. Coexistence of nonlinear optical switching behavior (space-group change from P21 to P21/n) and two-staged thermosensitive dielectric switching properties could be achieved under the stimulus of temperature. Our findings provide an effective approach for construction of polar materials.

Designing and Constructing a High-Temperature Molecular Ferroelectric by Anion and Cation Replacement in a Simple Crown Ether Clathrate

Molecular ferroelectrics have displayed a promising future since they are light-weight, flexible, environmentally friendly and easily synthesized, compared to traditional inorganic ferroelectrics. However, how to precisely design a molecular ferroelectric from a non-ferroelectric phase transition molecular system is still a great challenge. Here we designed and constructed a molecular ferroelectric by double regulation of the anion and cation in a simple crown ether clathrate, 4, [K(18-crown-6)]⁺ [PF₆ ]^- . By replacing K⁺ and PF₆ ^- with H₃ O⁺ and [FeCl₄ ]^- respectively, we obtained a new molecular ferroelectric [H₃ O(18-crown-6)]⁺ [FeCl₄ ]^- , 1. Compound 1 undergoes a para-ferroelectric phase transition near 350 K with symmetry change from P21/n to the Pmc21 space group. X-ray single-crystal diffraction analysis suggests that the phase transition was mainly triggered by the displacement motion of H₃ O⁺ and [FeCl₄ ]^- ions and twist motion of 18-crown-6 molecule. Strikingly, compound 1 shows high a Curie temperature (350 K), ultra-strong second harmonic generation signals (nearly 8 times of KDP), remarkable dielectric switching effect and large spontaneous polarization. We believe that this research will pave the way to design and build high-quality molecular ferroelectrics as well as their application in smart materials.

High-Temperature Reversible Phase-Transition Behavior, Switchable Dielectric and Second Harmonic Generation Response of Two Homochiral Crown Ether Clathrates

Crowning achievement: Two homochiral crown ether clathrates were synthesized which undergo high-temperature reversible phase transition. In addition, second harmonic generation (SHG) responses and abnormal dielectric property further confirm the reversible phase transitions and symmetry breaking behaviors of the structures.

High-temperature phase transitions, switchable dielectric behaviors and barocaloric effects in three new organic molecule-based crystals

Three new organic molecule-based compounds which undergo high-temperature phase transitions and display switchable dielectric behaviors.

Dielectric transitions and relaxations in Ca(ii)Co(iii)-based cyanometallate frameworks with a rare (6,6)-connected nia topology

A series of cyanometallate frameworks A[CaCo(CN)₆] (A = protonated guanidine, urea or thiourea guest) exhibit a rare (6,6)-connected nia topology with the Schläfli symbol of (4¹²·6³)(4⁹·6⁶) and thermally driven dielectric transitions and relaxations without evident structural phase transitions.

Prominent dielectric transitions in layered organic–inorganic hybrids: (isoamyl-ammonium)2CdX4 (X = Cl and Br)

Two new organic–inorganic layered perovskite-type hybrid compounds demonstrate different dynamic motions of cations, contributing to a significant difference in dielectric transitions.