Processing and piezoelectric properties of lead-free (K,Na) (Nb,Ta) O3 ceramics

The preparations of (K0.5Na0.5)NbO3 (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 sinterabillity and piezoelectric properties of these ceramics were dependent upon the A/B ratio, CuO doping, and the formation of a solid solution with KTaO3. Perovskite (K0.5Na0.5)(x)NbO3 (x = A/B ratio) was synthesized with A/B ratios of 1.00 and 1.05 by CuO doping, while (K0.5Na0.5)NbO3 contained K4CuNb8O23 as a second phase with A/B ratios below 0.98. Although the A site-rich (K(0.5)Nat(0.5))NbO3 (x = 1.00 and 1.05) ceramics exhibited deli-quescence, the A site-poor (K0.5Na0.5)NbO3 (x <= 0.98) ceramics with K4CuNb8O23 had higher densities without deliquescence. K4CuNb8O23 also improved Q(m), which reached 1400 for the (K0.5Na0.5)(1.0)NbO3 doped with 0.5 mol% K4CuNb8O23. The formation of a solid solution with KTaO3 raised the melting point of the system and also improved its sinterability. The k(p) and Q(m) of (K0.5Na0.5)(0.97)(Nb0.95Ta0.05)O-3 with CuO were 0.41 and 1400, respectively.