Revealing structure behavior behind the piezoelectric performance of prototype lead-free Bi0.5Na0.5TiO3BaTiO3 under in-situ electric field

Bi 0.5 Na 0.5 TiO 3 BaTiO 3 (BNT–100 x BT) 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 R 3 c and P 4 bm phases, their refined structures are significantly different. 6BT is composed of the R 3 c phase with a small P 4 bm 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.