The pre-annealed sintering method was attempted to obtain (K,Na)NbO₃ ceramics with a homogeneous microstructure without abnormal grain growth for multi-layered piezoelectric energy harvester application. The CuO and Na₂CO₃-doped (K,Na)NbO₃ ceramics by normal sintering at temperatures above 900 ^oC displayed excellent piezoelectric properties but showed an inhomogeneous microstructure due to an abnormal grain growth. Meanwhile, the ceramics sintered at temperatures of 880-900 ^oC showed a homogeneous microstructure and poor piezoelectric properties. The grain growth was influenced by a grain shape in a normal sintering. The sample that were sintered at temperatures of 880-900 ^oC with round-edged grains showed a normal grain growth, whereas samples sintered at temperatures above 900 ^oC with faceted grains exhibited abnormal grain growth. The specimen sintered at 940 ^oC for 3 hours after pre-annealing at 900 ^oC for 6 hours showed a homogeneous microstructure and excellent piezoelectric properties which are suitable for multi-layered piezoelectric energy harvesting applications. An electromechanical coupling factor (k_p), piezoelectric strain constant (d₃₃), and mechanical quality factor (Q_m) were 0.431, 143 pC/N, and 737, respectively and the figure of merits for a piezoelectric energy harvester in the resonance (k_p²∙Q_m) and off-resonance conditions (d₃₃∙g₃₃) were 137 and 7.5 pm²/N in the sample prepared by a pre-annealed sintering

Keywords: Piezoelectric, Pre-annealed sintering, (K,Na)NbO₃, Energy harvester