Effect of Li substitution on the piezoelectric properties of potassium sodium niobate ceramics

(K,Na,Li)NbO3 (KNN) ceramics with 0.38 mol % K5.4CU1.3Ta10O29 (KCT) have been prepared by a solid state reaction and their electrical properties were examined. The Curie temperature of (K,Na,Li)NbO3 increased with increasing Li substitution in both the Na and K sites. The 6 mol % Li-substituted sample showed a tetragonal phase at room temperature. Furthermore, a 1-2 mol % Li substitution for Na or K in (K0.5Na0.5)NbO3 improved several of its electrical properties. Most importantly, (K0.49Li0.01 Na-0.5)NbO3 attained high k(p) and Q(m) values of 0.43 and 2000, respectively. The value of the field-induced strain was also increased by substituting Li into (K0.5Na0.5)NbO3. The piezoelectric constant d(33) of (K0.5Li0.02Na0.48)NbO3 was approximately 200pm/V, which was calculated from the slope of the field-induced strain curve at 30-40kV/cm under a unipolar driving field.