The role of secondary phase in enhancing transduction coefficient of piezoelectric energy harvesting composites

Based on the strong requirement for self-powered devices, energy harvesting by utilizing piezoelectric materials has recently attracted extensive attention. Transduction coefficient (d33·g33) is the core parameter of the piezoelectric energy harvesting materials, which is directly determined by the ratio of the piezoelectric charge constant (d33) to the dielectric constant (er). Unfortunately, traditional solid solution design method generally causes a simultaneous increase or decrease in both d33 and er, making it difficult to obtain a high d33·g33. In this work, a composite design strategy was proposed to separate the synergistic change of d33 and er. This was achieved by introducing lower-er ZnAl2O4 secondary phase into the popular 0.2Pb(Zn1/3Nb2/3)O3–0.8Pb(Zr1/2Ti1/2)O3 (PZN–PZT) perovskite matrix. Encouragingly, the er value rapidly decreased, while d33 value improved within a certain range compared to those of pure PZN–PZT. This was ascribed to the formation of fine domain structures in composites caused by the heterogeneous interfacial effect. Subsequently, the cantilever beam type piezoelectric energy harvesters (PEHs) made from the optimal composites exhibited a high power density of 4.0 μW mm−3 at 1 g acceleration. More importantly, PEHs could harvest vibrational energy from the operating motor to charge a capacitor and instantly drive wireless micro-sensors, demonstrating their potential application in self-powered electronics. Under the guide of the composite design strategy proposed in this work, more high performance piezoelectric energy harvesting materials can be built in the future.