Giant electrostrictive strain in (Bi0.5Na0.5)TiO3–NaNbO3 lead-free relaxor antiferroelectrics featuring temperature and frequency stability

Abstract

Purely electrostrictive materials have shown outstanding advantages for high-precision actuators owing to characteristics such as being hysteresis free, having fast response and low ageing effect and so on. However, their limited achievable strain level, compared with that from piezoelectric materials or antiferroelectric phase-transition materials, and particularly significant temperature sensitivity have been a longstanding obstacle to actual applications in precise actuating or positioning under complex environmental conditions. In this work, a new specially designed lead-free perovskite solid solution was fabricated via a conventional solid-state process, which comprises NaNbO₃ (NN) with a high-Q₃₃ gene and (Bi_0.5Na_0.5)TiO₃ (BNT) with an intrinsically high spontaneous polarization gene. A giant purely electrostrictive strain of up to 0.20% varying within less than 10% in a wide temperature range of 25–250 °C and also nearly independent of frequency in the range of 0.01–100 Hz was achieved in the 0.76BNT–0.24NN ceramic, which shows hysteresis-free and linear P–E, S–P² and S–E² responses within a wide field range at least up to 20 kV mm⁻¹. The excellent electric field-displacement characteristics achieved in this system were basically ascribed to the existence of relaxor antiferroelectric anti-polar nanoregions with an ultrafast discharge (response) speed of ∼130 ns, as supported by in situ X-ray diffraction and transmission electron microscopy. The achievement of both high electrostrictive strain and excellent stability would make the BNT–NN binary ceramic suitable for large-displacement and high-accuracy actuators where high temperatures are specially required.