Ultrahigh strain in site engineering-independent Bi0.5Na0.5TiO3-based relaxor-ferroelectrics

In the past, accompanied by the highly asymmetric bipolar strain-electric field (S-E) loop, the ultrahigh strain can be realized in bismuth sodium titanate (BNT)-based ceramics mainly by the B site doping, which seriously restricts the further opening of the research and application scope. Here, regardless of A or/and B sites doping, we observed an ultrahigh unipolar strain response (S = 0.53-0.56% and d(33)* = 883-933 pm/V, 60 kV/cm) in [Bi-0.5(Na0.82-xK0.18Lix)(0.5)]((1-y))Sr-y(Ti1-zTaz)O-3 ceramics by chemical modifications, accompanied by the even higher unipolar strain (-0.63%, 90 kV/cm) and large field signal (d(33)* = 990 pm/V, 50 kV/cm). Moreover, the symmetrical bipolar S -E loop is also obtained in this system. In particular, we strictly illuminate the origin of the composition-induced giant strain from the view of the microscopic (A-O bonds weakening), mesoscopic (the coexistence of metastable small-sized ferroelectric domain structures and ergodic relaxor phase), and macroscopic (Tf-r shifting) perspectives. We believe that this work can provide a simple but effective way to optimize the strain behavior in BNT-based ceramics. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.