Figure 3
Phonon engineering to preserve the modes in ferroelectric against monoclinic non-polar modes inclusion and polarization switching. (A) Atomic structures of the orthorhombic and monoclinic phases of HfO2 and HCO superlattice. (B) Amplitude of the phonon modes that are condensed in the o-phase (blue open circle), o'-phase (filled blue circle), m-phase (red open square), and m'-phase (red filled square). The blue and red arrows show the increase in phonon amplitude in the o'- and m'-phases relative to their counterparts in HfO2. The blue dashed-line box contains the conserved modes of the o-phase in the o'-phase. (C) Energy barrier estimated by variable cell NEB calculations along the transition path between the monoclinic and orthorhombic phases of the superlattice (black filed circles) and HfO2 (red open circles). The dashed black, red and green lines indicate the energies of the tetragonal phases of the HCO, HfO2 and HZO, respectively, while \(\lambda\) represents the transition co-ordinate between their monoclinic and orthorhombic phases. Atomic structures of the up-polarized (D) and down-polarized (E) o'-phases of HCO. The silver oxygen atoms belong to the spacer layer whereas the red and yellow oxygen atoms belong to the up-polarized and down-polarized ferroelectric layers, respectively. (F) Energy landscape along the paths of switching homogeneous polarization via an intermediate tetragonal phase in the HCO superlattice (filled black circles), HfO2 (open red circles) and HZO superlattice (open green diamonds).
