Antiferroelectric-like properties and enhanced polarization of Cu-doped K0.5Na0.5NbO3 piezoelectric ceramics

Abnormal evolution of ferroelectric hysteresis (P-E) loops was observed in Cu-doped K0.5Na0.5NbO3 (KNN) ceramics. The 1 mol. % Cu-doped fresh sample exhibited double-loop-like characteristics, while the 1.5 and 2 mol. % Cu-doped KNN ceramics showed normal single loops. Electron paramagnetic resonance spectra verified the formation of non-switchable (CuNb[tprime]-VO times times ) ' (DC1) and non-polar (VO times times -CuNb[tprime]-VO times times ) times (DC2) defect complexes in these ceramics. According to the experimental results, it is suggested that DC1 would provide the driving force for domain back-switching, leading to the double P-E loops, while DC2 would contribute to the space charges. Dielectric aging behaviors of the samples also supported this mechanism. It is the competition between the DC1 and DC2 defect complexes that induced the observed compositional evolution of P-E loops in the Cu-doped KNN ceramics.