Optimized strain performance in <001>-textured Bi_0.5Na_0.5TiO₃-based ceramics with ergodic relaxor state and core–shell microstructure

Herein, a high strain of ~0.3% with a small hysteresis of 43% is achieved at a low electric field of 4 kV/mm in the highly <001>-textured 0.97(0.76Bi_0.5Na_0.5TiO₃–0.24SrTiO₃)–0.03NaNbO₃ (BNT–ST–0.03NN) ceramics with an ergodic relaxor (ER) state, leading to a large normalized strain (d₃₃^*) of 720 pm/V. The introduction of NN templates into BNT–ST induces the grain orientation growth and enhances the ergodicity. The highly <001>-textured BNT–ST–0.03NN ceramics display a pure ergodic relaxor state with coexisted ferroelectric R$\overline{3}$c and antiferroelectric P4bm polar nanoregions (PNRs) on nanoscale. Moreover, due to the incomplete interdiffusion between the NN template and BNT–ST matrix, the textured ceramics present a core–shell structure with the antiferroelectric NN core, and thus the BNT-based matrix owns more R$\overline{3}$c PNRs relative to the homogeneous nontextured samples. The high <001> crystallographic texture and more R$\overline{3}$c PNRs both facilitate the relaxor-to-ferroelectric transition, leading to the low-field-driven high strain, while the ergodic relaxor state ensures a small hysteresis. Furthermore, the d₃₃^* value remains high up to 518 pm/V at 100 ℃ with an ultra-low hysteresis of 6%.