Bi_0.5Na_0.5TiO₃BaTiO₃ (BNT–100xBT) ceramics are promising candidates for piezoelectric applications. The correlation between their structure and piezoelectric properties has attracted considerable interest. Herein, the structures of 6BT and 7BT with distinct piezoelectricity are investigated via in-situ synchrotron X-ray diffraction and transmission electron microscopy. It is found that although both compositions present morphotropic phase boundary (MPB) features with coexisting R3c and P4bm phases, their refined structures are significantly different. 6BT is composed of the R3c phase with a small P4bm fraction after electrical poling, while 7BT presents comparable fractions of the two phases. Less pronounced structure distortion and oxygen octahedral tilting occur in 7BT, which favor the phase transformation, resulting in an enhanced piezoelectricity. This enhancement driven by structural flexibility is elucidated by phenomenological analysis. These results demonstrate that the design of high piezoelectricity at MPBs should consider not only the phase-coexisting states but also the refined crystal structure.

Bi _0.5 Na _0.5 TiO ₃ BaTiO ₃ (BNT–100 x BT) 陶瓷是压电应用的有希望的候选材料。它们的结构和压电特性之间的相关性引起了相当大的兴趣。在此，通过原位同步辐射 X 射线衍射和透射电子显微镜研究了具有不同压电性的 6BT 和 7BT 的结构。研究发现，虽然这两种成分都存在共存的R 3 c和P 4 bm相的变形相界 (MPB) 特征，但它们的精细结构有显着差异。6BT 由R 3 c相在电极化后具有小的P 4 bm分数，而 7BT 呈现出两相的相当分数。在 7BT 中发生不太明显的结构变形和氧八面体倾斜，这有利于相变，从而提高压电性。这种由结构灵活性驱动的增强由现象学分析阐明。这些结果表明，MPB 的高压电性设计不仅应考虑相共存状态，还应考虑精细的晶体结构。