Highest-Tc single-component homochiral organic ferroelectrics

Precise Design of Molecular Ferroelectrics with High TC and Tunable Band Gap by Molecular Modification

Molecular ferroelectric materials are widely applied in piezoelectric converters, non-volatile memorizers, and photovoltaic devices due to their advantages of adjustable structure, lightweight, easy processing, and environmental friendliness. However, designing multifunctional molecular ferroelectrics with excellent properties has always been a great challenge. Herein, a multiaxial molecular ferroelectric is successfully designed by modifying the quasi-spherical cation dabco with CuBr₂ to obtain halogenated [Bretdabco]CuBr₄ (Bretdabco = N-bromoethyl-N'-diazabicyclo [2.2.2]octane), which crystallizes in polar point groups (C₆). Typical ferroelectric behaviors featured by the P-E hysteresis loop and switched ferroelectric domain are exhibited. Notably, the molecular ferroelectric shows a high T_C of 460 K, which is rare in the field and could greatly expand the application range of this material. In addition, the band gap is adjustable through the regulation of halogen. Both the UV absorption spectra and theoretical calculations indicate that the molecular ferroelectrics belong to a direct band gap (2.14 eV) semiconductor. This tunable and narrow band gap semiconductor molecular ferroelectric material with high T_C can be utilized more effectively in the study of optoelectronics and sensors, including piezoelectric energy harvesters. This research may provide a promising approach for the development of multiaxial molecular ferroelectrics with a tiny band gap and high T_C.

A room temperature ferroelectric material with photoluminescence: (1,3-dicyclohexylimidazole)2MnCl4

Molecular ferroelectric materials have been widely used in capacitors and sensors due to their low cost, light weight, flexibility and good biocompatibility. Organic-inorganic hybrid complexes, on the other hand, have received a great deal of attention in the luminescence field due to their low cost and simple preparation. The combination of ferroelectricity and photoluminescence in organic-inorganic hybrid materials not only leads to tunable optical properties, but also enriches potential applications of multifunctional ferroelectrics in optoelectronic devices. Here, we report a new luminescent ferroelectric material (1,3-dicyclohexylimidazole)₂MnCl₄ (DHIMC). Thermogravimetric analysis (TGA) was used to measure the mass change of the material at a measurement rate of 20 K min^-1 from room temperature to 900 K, and we found that this material has good thermostability, which is up to 383 K. Meanwhile, UV-vis measurements showed that it is also a fluorescent material emitting a strong green fluorescence at the wavelength of 525 nm. The ferroelectricity of the crystal was determined by two different methods: the Sawyer-Tower method and the double-wave method (DWM). Particularly, the single crystal experiences a phase transition from the ferroelectric phase to the paraelectric phase during the heating/cooling process at 318 K/313 K and the space group changes from P1̄ (centrosymmetric) to P1 (non-centrosymmetric). This work will enrich multifunctional luminescent ferroelectric materials and their application in display and sensing.

High-T c Single-Component Organosilicon Ferroelectric Crystal Obtained by H/F Substitution

Organic single-component ferroelectrics are highly desirable for their low molecular mass, light weight, low processing temperature, and excellent film-forming properties. Organosilicon materials with a strong film-forming ability, weather resistance, nontoxicity, odorlessness, and physiological inertia are very suitable for device applications related to the human body. However, the discovery of high-T _c organic single-component ferroelectrics has been very scarce, and the organosilicon ones even less so. Here, we used a chemical design strategy of H/F substitution to successfully synthesize a single-component organosilicon ferroelectric tetrakis(4-fluorophenylethynyl)silane (TFPES). Systematic characterizations and theory calculations revealed that, compared with the parent nonferroelectric tetrakis(phenylethynyl)silane, fluorination caused slight modifications of the lattice environment and intermolecular interactions, inducing a 4/mmmFmm2-type ferroelectric phase transition at a high T _c of 475 K in TFPES. To our knowledge, this T _c should be the highest among the reported organic single-component ferroelectrics, providing a wide operating temperature range for ferroelectrics. Moreover, fluorination also brought about a significant improvement in the piezoelectric performance. Combined with excellent film properties, the discovery of TFPES provides an efficient path for designing ferroelectrics suitable for biomedical and flexible electronic devices.

Chemical design of homochiral heterocyclic organic ferroelectric crystals

Single component organic ferroelectrics of spirooxazacamphorsultam derivatives, 1-SSR and 1-RRS, exhibit well-defined ferroelectricity (P_s = 2.2 μC cm^-2) and piezoelectricity (d₃₃ = 10 pC N^-1) below their melting point. More importantly, they possess a low acoustic impedance value of 2.7 × 10⁶ kg s^-1 m^-2, which is well-matched with body tissues.

An organic plastic ferroelectric with high Curie point

Plastic ferroelectrics, featuring large entropy changes in phase transitions, hold great potential application for solid-state refrigeration due to the electrocaloric effect. Although conventional ceramic ferroelectrics (e.g., BaTiO3 and KNbO3) have been widely investigated in the fields of electrocaloric material and catalysis, organic plastic ferroelectrics with a high Curie point (T c) are rarely reported but are of great importance for the sake of environmental protection. Here, we reported an organic plastic ferroelectric, (-)-camphanic acid, which crystallizes in the P21 space group, chiral polar 2 (C2) point group, at room temperature. It undergoes plastic paraelectric-to-ferroelectric phase transition with the Aizu notation of 23F2 and high T c of 414 K, showing large entropy gain (ΔS t = 48.2 J K-1 mol-1). More importantly, the rectangular polarization-electric field (P-E) hysteresis loop was recorded on the thin film samples with a large saturated polarization (P s) of 5.2 μC cm-2. The plastic phase transition is responsible for its multiaxial ferroelectric feature. This work highlights the discovery of organic multiaxial ferroelectrics driven by the motive of combining chirality and plastic phase transition, which will extensively promote the practical application of such unique functional materials.

An unprecedented azobenzene-based organic single-component ferroelectric

The first azobenzene-based organic single-component ferroelectric 2-amino-2′,4,4′,6,6′-pentafluoroazobenzene was designed, which shows an exceptionally high Curie temperature (Tc) of 443 K.