Self-Organized Ferroelastic Superdomains with Enhanced Piezoresponse in (101)-Oriented Pb(Zr_0.2,Ti_0.8)O₃Thin Films

Thin film engineering, utilizing proper control of crystalline orientation, strain, thickness, and defect density in thin films, has offered tremendous degrees of freedom for researchers to modify the physical properties, phase stability, and domain architectures in a wide spectrum of functional materials. This work unveils a naturally formed superdomain architecture arising from the low-orientation-symmetry-induced energetically degenerate state in a (101)-oriented tetragonal Pb(Zr,Ti)O3 epitaxial film. Different from conventional (101)-oriented/(110)-oriented domains found in (101)-oriented tetragonal Pb(Zr,Ti)O3 epitaxial heterostructures, these superdomains are composed of (101)-oriented domains with an alternative arrangement of opposite out-of-plane polarizations. Additionally, the conjunction between these superdomains has been found as another variant of the 90° domain wall that can exist in the low-symmetric preferred crystallographic orientation. The superdomains simultaneously exhibit an atypical piezoresponse hysteresis loop with additional metastable states, corresponding to the multistate ferroelastic domain switching process. This work gives distinct insight into the correlation between the domain pattern, lattice symmetry, and polarity switching, offering an effective way for exploring and engineering ultrafine domain features in tetragonal ferroelectrics.