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Epitaxial Ferroelectric Hf0.5 Zr0.5 O2 with Metallic Pyrochlore Oxide Electrodes.

  • Author(s): Zhang, Zimeng
  • Hsu, Shang-Lin
  • Stoica, Vladimir A
  • Paik, Hanjong
  • Parsonnet, Eric
  • Qualls, Alexander
  • Wang, Jianjun
  • Xie, Liang
  • Kumari, Mukesh
  • Das, Sujit
  • Leng, Zhinan
  • McBriarty, Martin
  • Proksch, Roger
  • Gruverman, Alexei
  • Schlom, Darrell G
  • Chen, Long-Qing
  • Salahuddin, Sayeef
  • Martin, Lane W
  • Ramesh, Ramamoorthy
  • et al.
Abstract

The synthesis of fully epitaxial ferroelectric Hf0.5 Zr0.5 O2 (HZO) thin films through the use of a conducting pyrochlore oxide electrode that acts as a structural and chemical template is reported. Such pyrochlores, exemplified by Pb2 Ir2 O7 (PIO) and Bi2 Ru2 O7 (BRO), exhibit metallic conductivity with room-temperature resistivity of <1 mΩ cm and are closely lattice matched to yttria-stabilized zirconia substrates as well as the HZO layers grown on top of them. Evidence for epitaxy and domain formation is established with X-ray diffraction and scanning transmission electron microscopy, which show that the c-axis of the HZO film is normal to the substrate surface. The emergence of the non-polar-monoclinic phase from the polar-orthorhombic phase is observed when the HZO film thickness is ≥≈30 nm. Thermodynamic analyses reveal the role of epitaxial strain and surface energy in stabilizing the polar phase as well as its coexistence with the non-polar-monoclinic phase as a function of film thickness.

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