Tuning phase structure for enhanced electrostrain in Nb⁵⁺-doped Bi_0.5(Na_0.81K_0.19)_0.5TiO₃ lead-free piezoelectric ceramics

The synthesis of Bi_0.5(Na_0.81K_0.19)_0.5Ti_1−xNb_xO₃ (BNKT-xNb) lead-free piezoelectric ceramics via the traditional solid-state method, with varying x from 0.5 % to 4.0 %, is reported. Investigating the influence of Nb⁵⁺ ions on dielectric, ferroelectric, and electrostrain properties, alongside assessing the temperature stability of electrical properties, unveiled a notable electrostrain of 0.46 % at room temperature under 80 kV/cm for the 2.0 mol.% Nb⁵⁺ doped composition. The incorporation of Nb⁵⁺ prompted a transition from the ferroelectric to the relaxor phase, facilitating reversible induction into the ferroelectric phase under an external electric field, leading to the observed large electrostrain. Leveraging the first-order reversal curve (FORC) approach, a detailed analysis of the dynamic response process of different phase structures under the influence of the external electric field was conducted. This analysis elucidated that the continuous polarization response near the boundary of ferroelectric and relaxor phases, induced by the external electric field, primarily drives strain enhancement. These findings underscore the effective modulation of phase structure through Nb⁵⁺ doping, offering significant advancements in strain properties. This study opens avenues for the utilization of the material in micro actuators and provides valuable insights for the development of high-performance lead-free piezoelectric ceramics.