Processing and Piezoelectric Properties of Lead‐Free (K,Na) (Nb,Ta) O ₃ Ceramics

Abstract

The preparations of (K 0.5 Na 0.5 )NbO 3 (KNN)‐based ceramics were studied as lead‐free piezoelectric materials. The authors found that the addition of CuO greatly enhanced the sinterability of the KNN‐based ceramics. The sinterability and piezoelectric properties of these ceramics were dependent upon the A/B ratio, CuO doping, and the formation of a solid solution with KTaO 3 . Perovskite (K 0.5 Na 0.5 ) x NbO 3 ( x =A/B ratio) was synthesized with A/B ratios of 1.00 and 1.05 by CuO doping, while (K 0.5 Na 0.5 )NbO 3 contained K 4 CuNb 8 O 23 as a second phase with A/B ratios below 0.98. Although the A site‐rich (K 0.5 Na 0.5 )NbO 3 ( x =1.00 and 1.05) ceramics exhibited deliquescence, the A site‐poor (K 0.5 Na 0.5 )NbO 3 ( x ≤0.98) ceramics with K 4 CuNb 8 O 23 had higher densities without deliquescence. K 4 CuNb 8 O 23 also improved Q m , which reached 1400 for the (K 0.5 Na 0.5 ) 1.0 NbO 3 doped with 0.5 mol% K 4 CuNb 8 O 23 . The formation of a solid solution with KTaO 3 raised the melting point of the system and also improved its sinterability. The k p and Q m of (K 0.5 Na 0.5 ) 0.97 (Nb 0.95 Ta 0.05 )O 3 with CuO were 0.41 and 1400, respectively.