Application of [001]-textured (K, Na)(Nb, Sb)O3-CaZrO3 thick films to piezoelectric energy harvesters

A (K, Na)NbO3 (KNN)-based lead-free piezoceramic for a piezoelectric energy harvester (PEH) should exhibit a large kij, Qm, dij, and a small εT33 to generate a large power output. Texturing was used to enhance the piezoelectricity of KNN-related piezoceramics. In particular, the kij and dij values of the KNN-based piezoceramics were considerably improved after texturing along the [001] direction, with a small change in the εT33/ε0 value, indicating that the [001]-textured KNN-based thick films are good candidates for use in PEHs. The 0.97(K0.5Na0.5)(Nb0.93Sb0.07)O3-0.03CaZrO3 [KN(N0.93S0.07)-CZ] thick film was textured along the [001] direction, and this thick film exhibited a large kp (0.57) and d33 × g33 (25.7 pm2/N), which is the largest d33 × g33 of the KNN-based piezoceramics reported to date. A cantilever PEH fabricated using the textured KN(N0.93S0.07)-CZ thick film exhibited a power density of 21.4 μW/mm3 at the resonance frequency. This is the highest power density observed for PEHs fabricated using lead-free piezoceramics. The PEH also exhibited a power density of 0.023 μW/mm3 at the off-resonance frequency. Therefore, the textured KN(N0.93S0.07)–CZ thick film is a good candidate for use in PEHs.