Hardening behavior and highly enhanced mechanical quality factor in (K_0.5Na_0.5)NbO₃–based ceramics

This paper relates the microstructure, crystallographic structure, ferroelectric, and piezoelectric properties of (K_0.5Na_0.5)NbO₃ (KNN) ceramics modified with 0.38 mol% K_5.4Cu_1.3Ta₁₀O₂₉ (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 (E_ib) increased from 0.3 kV/mm to 0.58 kV/mm at 0.5 mol% CuO–added KNN+KCT ceramics. The increase of E_ib corresponds very well with the observed increase of the mechanical quality factor (Q_m) 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 E_ib and the resulting hardening behavior.