Ideal barriers to polarization reversal and domain-wall motion in strained ferroelectric thin films

Abstract

The ideal intrinsic barriers to domain switching in $c$-phase ${\text{PbTiO}}_{3}$ (PTO), ${\text{PbZrO}}_{3}$ (PZO), and ${\text{PbZr}}_{1\ensuremath{-}x}{\text{Ti}}_{x}{\text{O}}_{3}$ (PZT) are investigated via first-principles computational methods. The effects of epitaxial strain on the atomic structure, ferroelectric response, barrier to coherent domain reversal, domain-wall energy, and barrier to domain-wall translation are studied. It is found that PTO has a larger polarization, but smaller energy barrier to domain reversal, than PZO. Consequentially the idealized coercive field is over two times smaller in PTO than PZO. The Ti-O bond length is more sensitive to strain than the other bonds in the crystals. This results in the polarization and domain-wall energy in PTO having greater sensitivity to strain than in PZO. Two ordered phases of PZT are considered, the rocksalt structure and a (100) PTO/PZO superlattice. In these simple structures we find that the ferroelectric properties do not obey Vergard's law, but instead can be approximated as an average over individual five-atom unit cells.