Harnessing Plasticity in an Amine‐Borane as a Piezoelectric and Pyroelectric Flexible Film

Ferroelectric Ionic Molecular Crystals with Significant Plasticity and a Low Melting Point: High Performance in Hot-Pressed Polycrystalline Plates and Melt-Grown Crystalline Sheets

Among ferroelectric crystals based on small molecules, plastic/ferroelectric crystals are currently receiving particular attention because they can be used as bulk polycrystals. Herein, we show that an ionic molecular ferroelectric crystal, guanidinium tetrafluoroborate, exhibits significant malleability and multiaxial ferroelectricity despite the absence of a plastic crystal phase. Powder samples of this crystal can be processed into transparent bulk crystalline plates either by press-forming or by melt-growing. The plates show high ferroelectric performance and related properties, demonstrating the largest hitherto reported spontaneous polarization for bulk polycrystals of small-molecule-based ferroelectrics. Owing to the ready availability of large-scale materials and processability into various bulk crystalline forms, this ferroelectric crystal represents a highly promising functional material that will boost research on diverse applications as bulk crystals.

Efficient Piezoelectric Energy Harvesting from a Discrete Hybrid Bismuth Bromide Ferroelectric Templated by Phosphonium Cation

Bismuth containing hybrid molecular ferroelectrics are receiving tremendous attention in recent years owing to their stable and non-toxic composition. However, these perovskite-like structures are primarily limited to ammonium cations. Herein, we report a new phosphonium based discrete perovskite-like hybrid ferroelectric with a formula [Me(Ph)₃ P]₃ [Bi₂ Br₉ ] (MTPBB) and its mechanical energy harvesting capability. The Polarization-Electric field (P-E) measurements resulted in a well-defined ferroelectric hysteresis loop with a remnant polarization value of 2.1 μC cm^-2 . Piezoresponse force microscopy experiments enabled visualization of the ferroelectric domain structure and evaluation of the piezoelectric strain coefficient (d₃₃ ) for an MTPBB single crystal and thin film sample. Furthermore, flexible devices incorporating MTPBB in polydimethylsiloxane (PDMS) matrix at various concentrations were fabricated and explored for their mechanical energy harvesting properties. The champion device with 20 wt % of MTPBB in PDMS rendered a maximum peak-to-peak open-circuit voltage of 22.9 V and a maximum power density of 7 μW cm^-2 at an optimal load of 4 MΩ. Moreover, the potential of MTPBB-based devices in low power electronics was demonstrated by storing the harvested energy in various electrolytic capacitors.

The Mechanism of Piezocatalysis: Energy Band Theory or Screening Charge Effect?

Piezocatalysis, a newly emerging catalysis technology that relies on the piezopotential and piezoelectric properties of the catalysts, is attracting unprecedented research enthusiasm for applications in energy conversion, organic synthesis, and environmental remediation. Despite the rapid development in the past three years, the mechanism of piezocatalysis is still under debate. A fundamental understanding of the working principles of this technology should enable the future design and optimization of piezocatalysts. Herein, we provide an overview of the two popular theories used to explain the observed piezocatalysis: energy band theory and screening charge effect. A comprehensive discussion and clarification of the differences, relevance, evidence, and contradiction of the two mechanisms are provided. Finally, challenges and perspectives for future mechanistic studies are highlighted. Hopefully, this Review can help readers gain a better understanding of piezocatalysis and enable its application in their own research.