Structure, dielectric, and piezoelectric properties of CuO-doped K0.5 Na0.5 Nb O3 -BaTi O3 lead-free ceramics

Lead-free piezoelectric ceramics (1-x) K0.5 Na0.5 Nb O3 +xBaTi O3 +y mol % CuO have been fabricated by an ordinary sintering technique. Our results show that the doping of CuO is effective in promoting the densification of the ceramics. With the doping of CuO, all the ceramics can be well sintered and exhibit a dense, pure perovskite structure. After the formation of a solid solution with BaTi O3, both the paraelectric cubic-ferroelectric tetragonal and ferroelectric tetragonal-ferroelectric orthorhombic phase transition temperatures decrease and a relax behavior is induced. Coexistence of the orthorhombic and tetragonal phases is formed in the ceramics with 0.04≤x≤0.06 and y=1.00 at room temperature. Because of the more possible polarization states arising from the coexistence of the two phases and the improved densification, the piezoelectric and dielectric properties of the ceramics are enhanced significantly. The ceramic with x=0.06 and y=1.00 exhibits the optimum properties: d33 =193 pCN, kp =0.43, kt =0.40, and TC =314 °C. On the other hand, the ceramics with 0≤x≤0.01 and y=1.0 exhibit excellent "hard" piezoelectric characteristics: kp ∼0.40, kt ∼0.47, Qm ∼1940, εr ∼230, and tan δ∼0.5%.