Ultrahigh Performance Piezoelectric Energy Harvester Using Lead-Free Piezoceramics with Large Electromechanical Coupling Factor

The output power of piezoelectric energy harvester (PEH) at the resonance frequency is dependent on the electromechanical coupling factor ( $k_p$ ) of the piezoceramic, which is proportional to $d_{33}/{\left({{\epsilon }^T}_{33}\right)}^{1/2}$ , where $d_{33}$ and ${{\epsilon }^T}_{33}$ are the piezoelectric change and dielectric constants, respectively. Therefore, the piezoceramic for the PEH should have a large $d_{33}$ and a small ${{\epsilon }^T}_{33}$ . [001]-texturing can be used for developing piezoceramics for PEH because it generally increases $d_{33}$ without increasing ${{\epsilon }^T}_{33}$ . The 0.96(K0.5Na0.5)(N1-zSz)O3-0.03(Bi0.5Ag0.5)ZrO3-0.01SrZrO3 [KN(N1-zSz)-BAZ-SZ] piezoceramics were textured along the [001] orientation, and the piezoceramic ( $z=0.01$ ) showed a large $k_p$ of 0.77, which is the largest $k_p$ for KNN-related piezoceramics reported in the literature. The cantilever-type PEH manufactured using the KN(N0.99S0.01)-BAZ-SZ piezoceramic exhibited a large output power density of 7.86 mW/cm3 at resonance frequency because of its large $k_p$ . To date, this is the largest power density for PEHs manufactured utilizing lead-free piezoceramics. Hence, the [001]-textured KN(N0.99S0.01)-BAZ-SZ piezoceramic is an excellent candidate for PEH, and [001]-texturing is a very efficient method for developing piezoceramics for PEH.