Ferroelectric materials are made of domains in which electric dipoles are all aligned in the same direction. The manipulation of these domains by an electric field ensures low energy consumption in electronic devices based on ferroelectrics. In our recent article published in Nature, we evidence the existence of an inverse transition, because it is apparently against fundamental thermodynamic principles, in ferroelectric thin films. Under the progressive increase of temperature, a labyrinthine phase of high symmetry transforms into the less-symmetric parallel stripe domain structure. Using first-principles based effective Hamiltonian computational modeling, we find that this counter-intuitive inverse phase sequence is ascribed to an enhanced entropic contribution of domain walls, and that domain straightening and coarsening is predominantly driven by the relaxation and diffusion of topological defects. These numerical calculations are performed in thin films of ferroelectric materials (Pb(Zr0.4Ti0.6)O3 and BiFeO3) that are intensively investigated for applications. This inverse transition is also observed experimentally in BiFeO3 thin films, suggesting the universality of the phenomenon in ferroelectric oxides. Furthermore, conductivity mappings at the nanometer scale reveal that the topological defects of the labyrinthine phase are characterized by an enhanced conduction that can be up to fifty times larger than the conduction at straight segments of domain walls. Thus, the inverse transition associated to the diffusion of topological defects can be electrically sensed, opening the path to possible applications. In the figure above, the upper panel shows the inverse transition from a labyrinthine structure of ferroelectric domains to a stripe domain structure of lower symmetry as a function of temperature. The lower panel presents the experimental confirmation of these numerical simulations in BiFeO3 thin films, indicating that the topological defects trapped in the labyrinthine structure show an enhanced conductivity.
This work was performed in collaboration with the Physics Department and Institute for Nanoscience and Engineering, University of Arkansas at Fayetteville and with the SPMS lab at Centrale/Supélec.
Inverse transition of labyrinthine domain patterns in ferroelectric thin films
Y. Nahas, S. Prokhorenko, J. Fischer, B. Xu, C. Carrétéro, S. Prosandeev, M. Bibes, S. Fusil, B. Dkhil, V. Garcia, L. Bellaiche
Nature 577, 47-51 (2020)