Giant electrostrictive strain in (Bi0.5Na0.5)TiO3-NaNbO3 lead-free relaxor antiferroelectrics featuring temperature and frequency stability
Purely electrostrictive materials have shown oustanding advantages for high-precision actuators owing to such characteristics as hysteresis free, fast response, low ageing effect and so on. However, limited achievable strain level, compared with that from piezoelectric materials or antiferroelectric phase-transition materials, and particularly its significant temperature sensitivity have been a longstanding obstacle to actual applications in precise actuating or positioning under complex environemnt conditions. In this work, a new specially-designed lead-free perovskite solid solution was fabricated via a conventional solid-state process, which comprises of NaNbO3 (NN) with high-Q33 gene and (Bi0.5Na0.5)TiO3 (BNT) with intrinisically 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 oC 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. The excellent electric field-displacement characteristics achieved in this system was basically ascribed to the existence of relaxor antiferroelectric polar nanoregions with an ultrafast discharge (response) speed of ~130 ns, as supported by using 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 be suited for large-displacement and high-accuracy actuators where high usage temperatures are specially required.