Hardening of K0.5Na0.5NbO3 piezoceramics with Cu and the temperature dependence in high-power drive

This study investigates the relationship between the electro-mechanical properties of Cu-doped potassium sodium niobate (KNN) piezoceramics driven at high vibration velocities and their structural origins. Intrinsic and extrinsic contributions to the dynamic strain were quantified at high-power resonance conditions by in-situ high-energy X-ray diffraction. These contributions were correlated to the observed sub-coercive dielectric and piezoelectric responses. Cu doping impairs extrinsic contributions of KNN due to the movement of non–180° domains, akin to acceptor-doped hard PZT, reducing the fraction of transverse strain originating from non–180° domain wall motion over the total strain of 5% at 0.8 m/s. Therefore, the performance of Cu-doped KNN and PZT were found to be comparable. Both systems exhibit a high mechanical quality factor at low vibration velocity, which decreases at high displacement rates. Additionally, the temperature dependence of electromechanical properties for different Cu doping amounts was investigated. In particular, the mechanical quality factor at the vibration velocity of 1 m/s in a temperature range of −40 °C to 140 °C was studied. According to the findings, the composition doped with 0.5% Cu exhibited a stable vibration at 1 m/s, with only 10% variation in the mechanical quality factor between 20 °C and 140 °C. • Intrinsic and extrinsic contributions to the strain of Cu-doped KNN ceramics driven in high power mode were quantified. • Cu-doped KNN system behaves in a similar fashion as hard PZT at high vibration velocity. • Cu doping reduces the transverse strain in KNN originating from non–180° domain wall motion over the total strain of 5%. • KNN doped with 0.5% Cu exhibits a stable mechanical quality factor and maximum vibration velocity.