Giant strain and excellent anti-fatigue properties of La³⁺ doped (Na_0.84K_0.16)_0.5Bi_0.5Ti_0.985Ta_0.015O₃ lead-free ceramics

Lead-free piezoelectric ceramics [(Na_0.84K_0.16)_0.5Bi_0.5]_1-xLa_xTi_0.985Ta_0.015O₃ (BNKTT-100xLa) were synthesized by traditional solid phase reaction. The influences of La³⁺ doping on ceramic materials’ microstructure, ferroelectric, and dielectric properties were investigated systematically. XRD patterns indicated that La³⁺ fully diffuse into the BNKTT lattice and form a single solid solution. SEM images showed that the surface of all samples was compact and no heterophase appeared. The ferroelectric-relaxor phase transition temperature gradually moved to low temperature with the increase of La³⁺ doping, which was beneficial to obtain large electro-strain. The maximum unipolar strain of BNKTT-1La ceramics can reach ∼0.439 % at 60 kV/cm corresponding to the inverse piezoelectric coefficient d₃₃^∗ of ∼731 pm/V. The strain performance increased significantly to ∼0.895 % at high temperature because the ferroelectric-relaxor phase transition became easier. The BNKTT-1La ceramics showed excellent fatigue resistance after 10⁵ cycles at 60 kV/cm. All these indicated that BNKTT-100xLa ceramics have great application prospects in piezoelectric brakes, strain sensors, and actuators.