With the rapid development of wearable devices, a highly sensitive flexible piezoelectric sensor shows tremendous potential for future demands. Here, we report a novel lead-free flexible piezoelectric sensor fabricated by a composite with chain-distributed (Ba_0.85Ca_0.15)(Ti_0.90Zr_0.10)O₃ (BCZT) particles in a polydimethylsiloxane (PDMS) matrix. The BCZT particles were prepared by a conventional solid oxide process and then dispersed in PDMS oriented by the application of a dielectrophoretic alignment field. The fabricated aligned flexible composite with 8 vol% BCZT addition had a high open circuit voltage of 28.8 V (peak-to-peak), which was nearly twice as high as that of the randomly dispersed composite. This new mechanically reinforced flexible piezoelectric composite was demonstrated to resolve the problems of the weak stress transfer to piezoelectric elements and the poor dispersion of fillers in the polymer matrix. The 8 vol% BCZT/PDMS composite was incorporated into a flexible piezoelectric touch sensor, which possesses excellent sensitivity in a wide pressure range and an extraordinary cycling stability. These results indicate that the fabricated flexible piezoelectric sensor has great potential in the wireless sensor network and wearable electronic fields.

High-performance lead-free piezoelectric materials have become a hot topic in the field of advanced functional materials. In 2009, the (1 − x)Ba(Zr0.2Ti0.8)O3–x(Ba0.7Ca0.3)TiO3 (BZT–BCT) system with surprisingly high piezoelectric properties was first proposed by Liu and Ren; as a milestone discovery in the field of ferroelectrics, it has aroused extensive attention. In this review, initially, we highlight the remarkable electrical properties of the BZT–BCT system, and then summarize the advances in the BZT–BCT material based on five aspects including the origin of its high properties, preparation and poling, grain size control, chemical modification and texture design. We focus on a systematic discussion of its phase boundaries, domain structure, and defect chemistry in relation to improved dielectric and piezoelectric properties. In addition, the device performance of BZT–BCT materials is also evaluated. Due to their excellent comprehensive properties, BZT–BCT materials have been widely studied in various applications such as energy harvesters, flexible sensors and energy storage capacitors. Finally, based on the state-of-the-art knowledge, we present an outlook on the challenges and application prospects of BZT–BCT materials. This review will help promote the practical applications of BZT–BCT materials, and accelerate the development of lead-free ferroelectric materials in specific fields.

Currently, effective piezoelectric energy harvesters are based on Pb(Zr,Ti)O₃ (PZT) ceramics. However, the growing environmental concerns have been pushing the development of viable green alternatives for lead-based piezoelectric ceramics. In this study, a high quality Mn-modified (K_0.5Na_0.5)NbO₃ (Mn-KNN) lead-free piezoelectric ceramic has been prepared, which is promising for use in lead-free piezoelectric energy harvesters. Herein, we showed that the 1.0 mol% Mn-KNN ceramics not only possessed high Curie temperature, but also exhibited excellent energy harvesting performance due to the highly dense fine-grained structure and various domain configurations. In the mode of a cantilever-type energy harvester, a high output power of 85 μW and peak-to-peak voltage of 16 V were obtained at the acceleration of 40 m s⁻². Furthermore, the 1.0 mol% Mn-KNN energy harvester exhibits excellent fatigue resistance up to 10⁶ cycles. These findings indicate potential applications of the Mn-KNN piezoelectric energy harvester for self-powered sources of wireless sensor network systems.