Hardening behavior and highly enhanced mechanical quality factor in (K0.5Na0.5)NbO3-based ceramics

This paper relates the microstructure, crystallographic structure, ferroelectric, and piezoelectric properties of (K0.5Na0.5)NbO3 (KNN) ceramics modified with 0.38 mol% K5.4Cu1.3Ta10O29 (KCT) and different amounts of CuO. Results revealed that the addition of KCT and CuO were effective in enhancing the sinterability of KNN. The internal bias field (Eib) increased from 0.3 kV/mm to 0.58 kV/mm at 0.5 mol% CuO-added KNN+KCT ceramics. The increase of Eib corresponds very well with the observed increase of the mechanical quality factor (Qm) from 112 to 2665 for 0.5 mol% CuO. Besides, addition of 0.5 mol% CuO to KNN+KCT resulted in a large increase of the EPR signal, which is related to the increased amount Cu2+ and a corresponding increase of the concentration of defect dipoles. This result is in good agreement with the increased Eib and the resulting hardening behavior.