Morphotropic phase boundary in (1−x)Bi[sub 0.5]Na[sub 0.5]TiO[sub 3]–xK[sub 0.5]Na[sub 0.5]NbO[sub 3] lead-free piezoceramics

The electromechanical behavior of (1−x)Bi0.5Na0.5TiO3–xK0.5Na0.5NbO3 (BNT-KNN) lead free piezoelectric ceramics is investigated for 0 <= x <= 0.12 to gain insight into the antiferroelectric-ferroelectric (AFE-FE) phase transition on the basis of the giant strain recently observed in BNT-based systems. At x ≈ 0.07, a morphotropic phase boundary (MPB) between a rhombohedral FE phase and a tetragonal AFE phase is found. While the piezoelectric coefficient is largest at this MPB, the total strain further increases with increasing KNN content, indicating the field-induced AFE-FE transition as the main reason for the large strain