High Q m values and humidity effect on the electrical properties of (K, Na)NbO 3 lead‐free piezoceramics doped with B 2 O 3 –CuO mixed oxides

To greatly enhance the mechanical quality factor ( Q m ) of piezoceramic materials, B 2 O 3 –CuO mixed oxides were added to a K 0.48 Na 0.52 NbO 3 ‐based lead‐free piezoceramic (abbreviated as BC ‐ KNN ). The results suggest that the B 2 O 3 –CuO additives effectively improved the sinterability and Q m value of the piezoceramic. An optimal Q m value as high as 2128 was obtained, which is 35 times higher than that of pure KNN ceramic. Interestingly, we found that the Q m value was sensitive to humidity of the surrounding environment. As the relative humidity ( RH ) increased from 25% RH to 78% RH , the Q m value of the BC ‐ KNN ceramics decreased from 2128 to 267. We found that the dependence of the Q m value on humidity was closely related to the instability of the relative dielectric constant (ɛ r ). Our results show that a dense microstructure is critical for maintaining a stable high Q m performance in a humid environment.