Structural dependence of piezoelectric, dielectric and ferroelectric properties of K0.5Na0.5(Nb1−2x/5Cux)O3 lead-free ceramics with high Qm

(K0.5Na0.5)(Nb1−2x/5Cux)O3 (abbreviated as KNNC, x = 0–2%) lead-free ceramics were synthetized by the solid state solution method. Pure perovskite phase with orthorhombic symmetry was observed. The evolution of the structure of KNNC was examined by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Raman scattering spectra techniques. Our results revealed that, defect dipoles ( C u ‴ Nb – V O ) ′ were formed and provided a restoring force to reverse the switched polarization, which resulted in double P–E hysteresis loops in KNNC with Cu doping at x = 0.75% and 1%. However, non-polar defect complex ( V O – C u ‴ Nb – V O ) caused a lattice shrinkage and the observed square shaped P–E loops in KNNC ceramics under high doping levels (x > 1%).