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.

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