Terahertz-range polar modes in domain-engineered BiFeO3


The dielectric permittivity and properties of electrically active lattice resonances in nanotwinned BiFeO3 crystals have been studied theoretically using an earlier established interatomic potential. The results suggest that an array of 71° domain walls with about 2–5 nm spacing enhances the static permittivity of BiFeO3 by more than an order of magnitude. This enhancement is associated with an electrically active excitation, corresponding to a collective vibration of pinned domain walls at a remarkably high frequency of about 0.3 THz.

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.