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

Abstract

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 (ε_r). Unfortunately, traditional solid solution design method generally causes a simultaneous increase or decrease in both d₃₃ and ε_r, 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 ε_r. This was achieved by introducing lower-ε_r ZnAl₂O₄ secondary phase into the popular 0.2Pb(Zn_1/3Nb_2/3)O₃–0.8Pb(Zr_1/2Ti_1/2)O₃ (PZN–PZT) perovskite matrix. Encouragingly, the ε_r 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.