Ferroelectrets: Recent developments

Ferroelectrets (also called piezoelectrets) are relatively young members in the family of piezo-, pyro- and ferroelectric materials. They exhibit ferroic behaviour phenomenologically undistinguishable from that of traditional ferroelectrics, although the materials per se are essentially non-polar space-charge electrets with artificial macroscopic dipoles (i.e. internally charged cavities). Since ferroelectrets not only represent a scientific curiosity but also have great application potential, they have attracted tremendous attention from science and industry. The research and development of ferroelectrets has witnessed significant progress in the past few years. New ferroelectrets with large transverse piezoelectric activity, biodegradable ferroelectrets as well as 3-D printed ferroelectrets are reported. Charging methods of high efficiency are proposed based on better understanding of the physico-chemical processes during charging. New insights into the piezoelectricity of ferroelectrets are provided. The development of ferroelectret-based piezoelectric-magnetic multimodal transducer films opens up new avenues for the research of ferroelectrets. Particularly, more and more novel applications of ferroelectrets in flexible pressure sensors, health monitoring, energy harvesting, air-coupled ultrasonic non-destructive testing etc. are reported. Here, these exciting recent advancements in the field of ferroelectret research are reviewed and discussed.