Influence of compositional ratio K/Na on structure and piezoelectric properties in [(Na_1−xK _x)_0.5Bi_0.5]Ti_0.985Ta_0.015O₃ ceramics

[(Na_1−xK_x)_0.5Bi_0.5]Ti_0.985Ta_0.015O₃ (abbreviated as Ta-NK100x) lead-free ceramics with good piezoelectric properties were prepared using a solid-state reaction method. The structure and electrical properties of Ta-NK100x had been systemically investigated. The highest bipolar strain of 0.458% and the unipolar strain 0.448% are achieved at x = 0.18 at 60 kV/cm. Meanwhile, the corresponding normalized strain (d33∗) reaches 747 pm/V. In addition, the unipolar strain of the poled Ta-NK18 increases to 0.537%, and corresponding d33∗ increases slightly to 894.5 pm/V at 60 kV/cm. The electric-field-induced phase transition between ferroelectric and relaxor is found to play a dominant role in the origin of the large strain. Moreover, the strain behavior remains stable within 10⁵ switching cycles which indicating the prepared ceramics are promising candidates for actuators and stress sensors.