Structural dependence of piezoelectric, dielectric and ferroelectric properties of K _0.5Na _0.5(Nb _1-2x/5Cu _x)O ₃ lead-free ceramics with high Q _m

(K _0.5Na _0.5)(Nb _1-2x/5Cu _x)O ₃ (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 (Cu''' _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••-Cu''' _Nb-V _O••) • caused a lattice shrinkage and the observed square shaped P-E loops in KNNC ceramics under high doping levels (x > 1%).