Temperature‐insensitive strain behavior in 0.99[(1− x )Bi 0.5 (Na 0.80 K 0.20 ) 0.5 TiO 3 − x BiFeO 3 ]–0.01Ta lead‐free piezoelectric ceramics

Lead‐free 0.99[(1− x )Bi 0.5 (Na 0.80 K 0.20 ) 0.5 TiO 3 − x BiFeO 3 ]–0.01Ta ( BNKT 20–100 x BF –1Ta) lead‐free piezoelectric ceramics were fabricated through conventional solid state sintering method. Results showed that change of BF content in the BNKT 20–100 x BF –1Ta induced a phase transition from ferroelectric to ergodic relaxor phase with a significant disruption of the long‐range ferroelectric order. A large electric‐field‐induced strain of 0.36% (at 80 kV/cm driving field, corresponding to a large signal d 33∗of ~450 pm/V) which is derived from a reversible field‐induced ergodic relaxor to ferroelectric phase transformation, was obtained in the composition with x =0.01 near the ferroelectric‐ergodic relaxor phase boundary. Moreover, an attractive property for application in nonlinear actuators demanding enhanced thermal stability was obtained in this material, which showed a temperature‐insensitive strain characteristic in the temperature range from room temperature to 100°C.