Tailoring frequency-insensitive large field-induced strain and energy storage properties in (BaCa)(ZrTi)O-modified (BiNa)TiO lead-free ceramics.

Lead-free (BiNa)TiO-based relaxor ferroelectrics are attracting growing research interest due to their very large field-induced strain response and excellent energy storage performance. While extensive explorations have been made of these performances separately, being able to optimize both field-induced strain and energy storage performance of polycrystalline materials together, and hence achieve a synergistic result, would also be highly desirable for their practical applications. Herein, lead-free relaxor-ferroelectric (BaCa)(ZrTi)O-modified (BiNa)TiO (BNT-BCZT) ceramics were designed and demonstrated to be feasible candidates for both actuator and pulsed power capacitors. Optimal field-induced strain performances were realized in 0.92BNT-0.08BCZT ceramics with not only a high strain of 0.46% but also an impressive frequency stability (0.5 Hz-100 Hz), superior to those of other reported BNT-based materials under a similar frequency range. Moreover, the 0.5BNT-0.5BCZT compositions in the complete ER region delivered a relatively high W of 0.95 J cm and η of 69%, while still remaining insensitive to changes in temperature, frequency, and cycle number. More importantly, a short discharge time (of ∼0.41 μs) was also measured for this composition. Introducing BCZT into the composition was found to promote a non-ergodic-to-ergodic relaxor (NR-ER) phase transition and the formation of dynamic polar nanoregions (PNRs), generating the high strain responses and superior energy storage performances of the given compositions. These features may offer a new strategy to simultaneously tailor lead-free relaxor ferroelectrics toward high field-induced strain and superior energy storage performance for ceramics actuators and capacitor applications.