Giant strain and excellent anti-fatigue properties of La3+ doped (Na0.84K0.16)0.5Bi0.5Ti0.985Ta0.015O3 lead-free ceramics

Lead-free piezoelectric ceramics [(Na0.84K0.16)0.5Bi0.5]1-xLaxTi0.985Ta0.015O3 (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.