LAUSR

Ferroelastic-ferroelectrics are multi-functional materials with attractive applications such as actuator, memory devices and flexible/wearable electronic devices [1-7]. This class of intrinsically brittle materials exhibits unique unconventional deformation mechanisms that could be potentially utilized to engineer novel electric-mechanical components. Notably, the close-correlated domain evolutions and phase transformations in ferroelastic-ferroelectrics is reported to generate a complex hierarchical structure that is responsible to the superelastic deformation behaviors of the materials at nanoscale [7]. By applying high stress to the material, hierarchical nanodomain evolutions can be introduced into ferroelasticferroelectrics, effectively tuning their properties. However, the complex nanodomain evolutions are challenging to understand: the domain mobility, the distributions of local strains and mobile point defects at domain walls, and the growth of the bundle domain structures have been discussed for a long time with controversy [1,2]. Small scale mechanical in-situ TEM observations provide unique real-time capability of capturing the nanodomain evolution while the stress field is applied. Here, by applying in situ TEM mechanical tests couple with 4D-STEM techniques that are capable of generating nm-resolved strain mapping in an aberration-corrected transmission electron microscope [1,4,5,6], we studied free-standing