Effect of K/Na ratio on piezoelectric properties of modified-(K1−xNax)NbO3 “Hard” lead-free piezoelectrics

0.55 mol% K4CuNb8O23–(K1−xNax)NbO3 (KCN–KNNx) with 0.45 ≤ x ≤ 0.60 were synthesized by conventional method. Results revealed that the increase of x was effective in changing the microstructure and relative density of KCN–KNNx. Further, varying the x resulted in a slight shift of the phase transition temperatures (To–t and Tc) toward low values. A high mechanical quality factor (Qm) of 1850 was found at x = 0.54, which might be due to the build-up of an internal bias field (Ei) within KCN. Thermal hysteresis in KCN–KNNx was confirmed with x, resulting from structural changes. Thus, KCN–KNNx with x = 0.54 exhibits excellent piezoelectric properties with d33 (97 pC/N), kp (36%), and Qm (1850), being promising candidates for application in high-power piezoelectric devices.