Electro-shape-memory effect in Mn-doped BaTiO₃ single crystals and in situ observation of the reversible domain switching

Very recently a giant electric-field-induced recoverable shape change effect (electro-shape-memory effect) has been found in aged BaTiO₃-based ferroelectric crystals. This effect is supposed to come from a reversible domain-switching process with the restoring force provided by a symmetry-conforming principle of defects. However, the reversible domain switching process itself behind the giant electro-shape-memory effect is yet to be directly verified. In the present study, we performed in situ domain observation during electric field cycling for aged Mn-doped BaTiO₃ single crystals and simultaneously measured its macroscopic properties. It was found that the aged sample shows a reversible domain switching during electric field cycling; this corresponds very well to the electro-shape-memory effect (with a maximum shape change of 0.4%, which is almost half of the theoretical value). This provides a direct mesoscopic evidence for the defect-mediated reversible domain switching mechanism. Moreover, as all these effects stems from aging in ferroelectric state, we further explained that their microscopic origin is symmetry-conforming property of defects, which is completed during aging by defect migration.