Solvent Selective Effect Occurs in Iodinated Adamantanone Ferroelectrics

Biodegradable ferroelectric molecular crystal with large piezoelectric response

Transient implantable piezoelectric materials are desirable for biosensing, drug delivery, tissue regeneration, and antimicrobial and tumor therapy. For use in the human body, they must show flexibility, biocompatibility, and biodegradability. These requirements are challenging for conventional inorganic piezoelectric oxides and piezoelectric polymers. We discovered high piezoelectricity in a molecular crystal HOCH2(CF2)3CH2OH [2,2,3,3,4,4-hexafluoropentane-1,5-diol (HFPD)] with a large piezoelectric coefficient d33 of ~138 picocoulombs per newton and piezoelectric voltage constant g33 of ~2450 × 10-3 volt-meters per newton under no poling conditions, which also exhibits good biocompatibility toward biological cells and desirable biodegradation and biosafety in physiological environments. HFPD can be composite with polyvinyl alcohol to form flexible piezoelectric films with a d33 of 34.3 picocoulombs per newton. Our material demonstrates the ability for molecular crystals to have attractive piezoelectric properties and should be of interest for applications in transient implantable electromechanical devices.

High-Temperature Phase Transition with Switchable Dielectric Behavior and Significant Photoluminescence Changes in a Zero-Dimensional Hybrid SbBr6 Perovskite

In the past decade, metal halide materials have been favored by many researchers because of their excellent physical and chemical properties under thermal, electrical, and light stimuli, such as ferroelectricity, dielectric, nonlinearity, fluorescence, and semiconductors, greatly promoting their application in optoelectronic devices. In this study, we successfully constructed an unleaded organic-inorganic hybrid perovskite crystal: [Cl-C6H4-(CH2)2NH3]3SbBr6 (1), which underwent a high-temperature reversible phase transition near Tp = 368 K. The phase transition behavior of 1 was characterized by differential scanning calorimetry, accompanied by a thermal hysteresis of 6 K. In addition, variable-temperature Raman spectroscopy analysis and PXRD further verified the sensitivity of 1 to temperature and the phase transition from low symmetry to high symmetry. Temperature-dependent dielectric testing shows that 1 can be a sensitive switching dielectric constant switching material. Remarkably, 1 exhibits strong photoluminescence emission with a wavelength of 478 nm and a narrow band gap of 2.7 eV in semiconductors. As the temperature increases and decreases, fluorescence undergoes significant changes, especially near Tc, which further confirms the reversible phase transition of 1. All of these findings provide new avenues for designing and assembling new phase change materials with high Tp and photoluminescence properties.

Organic radical ferroelectric crystals with martensitic phase transition

Organic martensitic compounds are an emerging type of smart material with intriguing physical properties including thermosalient effect, ferroelasticity, and shape memory effect. However, due to the high structural symmetry and limited design theories for these materials, the combination of ferroelectricity and martensitic transformation has rarely been found in organic systems. Here, based on the chemical design strategies for molecular ferroelectrics, we show a series of asymmetric 1,4,5,8-naphthalenediimide derivatives with the homochiral amine and 2,2,6,6-tetramethylpiperidine-N-oxyl components, which adopt the low-symmetric polar structure and so allow ferroelectricity. Upon H/F substitution, the fluorinated compounds exhibit reversible ferroelectric and martensitic transitions at 399 K accompanied by a large thermal hysteresis of 132 K. This large thermal hysteresis with two competing (meta)-stable phases is further confirmed by density functional theory calculations. The rare combination of martensitic phase transition and ferroelectricity realizes the bistability with two different ferroelectric phases at room temperature. Our finding provides insight into the exploration of martensitic ferroelectric compounds with potential applications in switchable memory devices, soft robotics, and smart actuators.

A Cd-based perovskite with optical-electrical multifunctional response

Two-dimensional (2D) organic-inorganic hybrid perovskites (OIHPs) have drawn tremendous attention on account of their structural tunability, simple synthesis mothed, superior properties. Among them, 2D cadmium-based perovskites, exhibiting reversible phase transition,...