Phase Characteristics and Piezoelectric Properties in the Bi0.5Na0.5TiO3-BaTiO3-K0.5Na0.5NbO3 System

Lead-free 0.94Bi(0.5)Na(0.5)TiO(3)-(0.06-x)BaTiO3-xK(0.5)Na(0.5)NbO(3) (x=0-0.06) ceramics were prepared. All these compositions have a structure close to the rhombohedral-tetragonal morphotropic phase boundary (MPB) and good electric properties at room temperature. No significant composition dependence of ferroelectric property can be established, whereas a dependence of piezoelectric properties can be observed, e.g. the piezoelectric coefficient (d(33)), planar coupling factor (k(p)), and field-induced strain (S) increase with increasing x when x < 0.01 and then tend to decrease. The highest d(33), k(p), and bipolar strain are 118 pC/N, 0.29, and 0.32%, respectively, in the composition with x=0.01. The results not only indicate that BNT-BT-KNN lead-free piezoceramics can persist in the structure close to MPB in a wide composition range but that they may also be helpful for further investigation on lead-free piezoceramics.