Significantly enhanced mechanical quality factor with favorable piezoelectricity in K0.5Na0.5NbO3 based ceramics

The apparent incompatibility between d(33) and Q(m) in potassium sodium niobate-based lead-free ceramics is an obstacle to their applications. In this study, (K0.5Na0.5)(0.98)Li0.02Nb0.82Ta0.18O3 (LT-KNN) system near the orthorhombic-tetragonal (O-T) phase boundary but in the O phase region is selected as the matrix to ensure a relatively large d(33) and high Tc, and help the CuO doping generate an effective "hardening" effect to improve Q(m). The results show that adding proper amount of CuO into LT-KNN promotes the densification of ceramics and suppresses the abnormal grain growth, which helps to decrease the dielectric loss and obtain a high poling efficiency. Moreover, the Cu2+ doping in B-site (Nb/Ta)(5+) generates oxygen vacancies (V-o(center dot center dot)) and the (Cu-Nb/Ta''' - V-o(center dot center dot))(')( )defect dipoles could be formed, resulting an obvious "hardening" effect. With the introduction of 1 mol% CuO, the d(33) increases from 82 to 180 pC/N and the Q(m) presents an abrupt rise from 136 to 665. More intriguingly, the addition of CuO delays the O-T phase transition while maintaining a high Tc of similar to 310 degrees C. Combined with the pinning effect of internal bias field, the d(33) of 1 mol% CuO doped LT-KNN ceramics shows favorable stability in the wide temperature range of 20-280 degrees C, and a high Q(m )of larger than 250 can be achieved until 100 degrees C. Such a superior comprehensive electromechanical performance makes the ceramics promising in applications of high-power and high-frequency devices.