High Normalized Strain Obtained in Li-Modified (K,Na)NbO3 Lead-Free Piezoceramics

Lead-free Li-(K,Na)NbO3 (KNN) piezoceramics shows surprisingly high normalized strain d(33)* up to 538 pm/V at electric fields as low as 1 kV/mm, comparable to a commercial soft lead zirconate titanate (PZT) sample. The special treating process of aging and re-poling is essential for this achievement. The extrinsic piezoelectric contribution related to domain wall motion is proposed of primary responsibility for the strain, which endows the sample with a direct piezoelectric coefficient of 324 pC/N. Strain behavior with regard to both electric field level and frequency was investigated to prove the assumption. The present study proves the possibility of preparing PZT-comparable lead-free piezoceramics in simply Li-doped KNN by conventional sintering. (C) 2011 The Japan Society of Applied Physics