A detailed overview on interface design and control in polymer based composite dielectrics for energy storage applications.

This paper demonstrates the significant benefits of exploiting highly aligned porosity in piezoelectric and pyroelectric materials for improved energy harvesting performance. Porous lead zirconate (PZT) ceramics with aligned pore channels and varying fractions of porosity were manufactured in a water-based suspension using freeze-casting. The aligned porous PZT ceramics were characterized in detail for both piezoelectric and pyroelectric properties and their energy harvesting performance figures of merit were assessed parallel and perpendicular to the freezing direction. As a result of the introduction of porosity into the ceramic microstructure, high piezoelectric and pyroelectric harvesting figures of merits were achieved for porous freeze-cast PZT compared to dense PZT due to the reduced permittivity and volume specific heat capacity. Experimental results were compared to parallel and series analytical models with good agreement and the PZT with porosity aligned parallel to the freezing direction exhibited the highest piezoelectric and pyroelectric harvesting response; this was a result of the enhanced interconnectivity of the ferroelectric material along the poling direction and reduced fraction of unpoled material that leads to a higher polarization. A complete thermal energy harvesting system, composed of a parallel-aligned PZT harvester element and an AC/DC converter, was successfully demonstrated by charging a storage capacitor. The maximum energy density generated by the 60 vol% porous parallel-connected PZT when subjected to thermal oscillations was 1653 μJ cm⁻³, which was 374% higher than that of the dense PZT with an energy density of 446 μJ cm⁻³. The results are beneficial for the design and manufacture of high performance porous pyroelectric and piezoelectric materials in devices for energy harvesting and sensor applications.

Nonvolatile memories are in strong demand due to the desire for miniaturization, high-speed storage, and low energy consumption to fulfill the rapid developments of big data, the Internet of Things, and artificial intelligence. Hafnia (HfO₂)-based materials have attracted significant interest due to the advantages of complementary-metal–oxide–semiconductor (CMOS) compatibility, large coercive voltage, and superior ferroelectricity at an ultra-thin thickness. The comparable ferroelectricity to that of traditional perovskite materials and size advantage of HfO₂ result in fascinating storage performance, which can be readily applicable to the fields of integrated non-volatile memories. This Review provides a comprehensive overview of recent developments in HfO₂-based ferroelectrics with attention to the origin of ferroelectricity, performance modulation, and recent achievements in the material. Moreover, potential solutions to existing challenges associated with the materials are discussed in detail, including the wake-up effect, long-term fatigue behavior, and imprint challenges, which pave the way for obtaining HfO₂-based ferroelectric materials and devices with long service life and high stability. Finally, the range of potential applications for these fascinating new materials is presented and summarized, which include non-volatile memories and neuromorphic systems. This Review intends to present the state-of-the-art HfO₂-based ferroelectrics and to highlight the current challenges, possible applications, and future opportunities and can act as an update for recent developments in these intriguing materials and provide guidance for future researchers in the design and optimization of HfO₂-based ferroelectric materials and devices.

Polymer dielectrics are attracting increasing attention for electrical energy storage owing to their advantages of mechanical flexibility, corrosion resistance, facile processability, light weight, great reliability, and high operating voltages. However, the dielectric constants of most dielectric polymers are less than 10, which results in low energy densities and limits their applications in electrostatic capacitors for advanced electronics and electrical power systems. Therefore, intensive efforts have been placed on the development of high‐energy‐density polymer dielectrics. In this perspective, the most recent results on the all‐organic polymer dielectrics are summarized, including molecular structure design, polymer blends, and layered structured polymers. The challenges in the field and suggestions for future research on high‐energy‐density polymer dielectrics are also presented.