Strain‐Driven Mixed‐Phase Domain Architectures and Topological Transitions in Pb1−xSrxTiO3 Thin Films

The potential for creating hierarchical domain structures, or mixtures of energetically degenerate phases with distinct patterns that can be modified continually, in ferroelectric thin films offers a pathway to control their mesoscale structure beyond lattice‐mismatch strain with a substrate. Here, it is demonstrated that varying the strontium content provides deterministic strain‐driven control of hierarchical domain structures in Pb1−xSrxTiO3 solid‐solution thin films wherein two types, c/a and a1/a2, of nanodomains can coexist. Combining phase‐field simulations, epitaxial thin‐film growth, detailed structural, domain, and physical‐property characterization, it is observed that the system undergoes a gradual transformation (with increasing strontium content) from droplet‐like a1/a2 domains in a c/a domain matrix, to a connected‐labyrinth geometry of c/a domains, to a disconnected labyrinth structure of the same, and, finally, to droplet‐like c/a domains in an a1/a2 domain matrix. A relationship between the different mixed‐phase modulation patterns and its topological nature is established. Annealing the connected‐labyrinth structure leads to domain coarsening forming distinctive regions of parallel c/a and a1/a2 domain stripes, offering additional design flexibility. Finally, it is found that the connected‐labyrinth domain patterns exhibit the highest dielectric permittivity. It is numerically and experimentally shown that, by controlling strontium content and in turn manipulating strain, topologically non‐trivial phase arrangements appear in hierarchical, mixed‐phase domains structure of Pb1−xSrxTiO3. These phases showcase a variety of pattern defects that can be manipulated via thermal treatment. In turn, the dielectric response, which is strongly correlated with domain structure, can be widely varied.