High-power piezoelectric energy harvester produced using [0 0 1]-textured (Na, K)NbO₃-based lead-free piezoceramics

High-power piezoelectric energy harvesters (PEHs) require piezoceramics with a large k_p and d₃₃ but small ε^T₃₃/ε₀ values. The [0 0 1]-textured 0.96(Na, K)(Nb_1−xSb_x)–0.04SrZrO₃ piezoceramics (x = 0.025 and 0.045) exhibited the improved electromechanical coupling factor (k_p) and piezoelectric charge constant (d₃₃); however, the increase of dielectric constant (ε^T₃₃/ε₀) was not significant. Further, the textured piezoceramic with x = 0.045 shows the large d₃₃ × g₃₃ value of 21.5 pm²/N, where g₃₃ is piezoelectric voltage constant, indicating that texturing is a good technique to fabricate the piezoceramics for PEH. The impedance curve of the PEH consisting of the metal substrate and textured piezoceramic shows a piezoelectric resonance peak at a low frequency, which is the same as the mechanical resonance frequency of the PEH. Hence, the PEH can be considered a piezoelectric material. The figure of merit of the PEH was determined using the mechanical quality and electromechanical coupling factor calculated from the impedance curve of the PEH. A large power output of 1.7 mW was obtained from the type-1 PEH at the resonance frequency produced using the textured thick film (x = 0.045). Hence, this PEH can be used as a permanent power source for microelectronic devices in the Internet of Things.