Regional consistency between cation displacement and oxygen octahedral tilt in nanodomain of BNKT-SBT relaxor ferroelectrics revealed by atomic-resolution AC-STEM

Since being discovered, relaxor ferroelectrics have attracted continued interest due to their unusual properties. Relaxor behavior is attributed to nanodomains or PNRs. Therefore, nano-scale even atomic-scale structural analysis is crucial to understanding the relaxor properties. However, the atomic-scale nanodomain structure has not been fully understood. For Bi_0.5Na_0.5TiO₃, cation displacement and oxygen octahedral tilt are two common structural distortions. However, the relationship between them has not been proved experimentally. Here, the cation displacement and octahedral tilt were both investigated based on aberration-corrected STEM images. Cation displacement vectors illustrate a vortex structure. Octahedral tilt is regionally consistent with cation displacement that both of them increase gradually from the domain wall to the interior of the nanodomain. The formation of nanodomains may originate from their combined effect, thereby producing relaxor properties. Moreover, oxygen octahedral displacement stemmed from the complex coordinating environments was observed. These findings provide further insights into the nanodomain structure.