Three‐State Ferroelastic Switching and Large Electromechanical Responses in PbTiO3 Thin Films

Leveraging competition between energetically degenerate states to achieve large field‐driven responses is a hallmark of functional materials, but routes to such competition are limited. Here, a new route to such effects involving domain‐structure competition is demonstrated, which arises from strain‐induced spontaneous partitioning of PbTiO3 thin films into nearly energetically degenerate, hierarchical domain architectures of coexisting c/a and a1/a2 domain structures. Using band‐excitation piezoresponse force microscopy, this study manipulates and acoustically detects a facile interconversion of different ferroelastic variants via a two‐step, three‐state ferroelastic switching process (out‐of‐plane polarized c+ → in‐plane polarized a → out‐of‐plane polarized c− state), which is concomitant with large nonvolatile electromechanical strains (≈1.25%) and tunability of the local piezoresponse and elastic modulus (>23%). It is further demonstrated that deterministic, nonvolatile writing/erasure of large‐area patterns of this electromechanical response is possible, thus showing a new pathway to improved function and properties. Strain‐induced structural competition between domain‐structure variants of tetragonal PbTiO3 drives the formation of exotic hierarchical domain patterns, as indicated by the complex topography observed in scanning‐probe‐based studies. This competition also promotes facile interconversion between in‐ and out‐of‐plane polarized ferroelastic variants, which is concomitant with large nonvolatile electromechanical strains, and tunability of local piezoresponse and elastic modulus. There is rich potential for on‐demand electrical writing of ferroelastic mesostructures.