(K0.5Na0.5)(Nb1-2x/5Cux)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(circle circle))' 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(circle circle)-Cu-Nb(''')-V-o(circle circle))(circle) caused a lattice shrinkage and the observed square shaped P-E loops in KNNC ceramics under high doping levels (x > 1%). (C) 2012 Elsevier Ltd. All rights reserved.