Domain wall contribution to lattice dynamics and permittivity of BiFeO₃

Ferroelectric materials are known for their exceptionally high dielectric permittivity. It turns out, that important part of it originates from a material's complicated microstructure and in particular from interfaces between ferroelectric domains. In this study we investigate different types of interfaces in a multiferroic BiFeO₃. By means of atomistic modelling we show that some configurations of interfaces can greatly enhance the permittivity by hosting terahertz-range collective polar fluctuations. The key result is that the permittivity is modified in the THz range. This fundamental finding and its understanding can be used in a design of new materials [ J. Hlinka, M. Pasciak, S. Körbel, and P. Márton, Phys. Rev. Lett. 119, 057604 (2017)].

Figure: Change of the (polar-active) phonon spectrum due to presence of dense domain-interface structure of BiFeO₃ (right panel) in comparison with the single-domain case (left panel). Additional low-frequency Γ-point mode (labelled A) is responsible for 25x enhancement of permittivity in the domain engineered material.