Epitaxial Ferroelectric Hf<sub>0.5</sub> Zr<sub>0.5</sub> O<sub>2</sub> with Metallic Pyrochlore Oxide Electrodes.
basic_science · Level V
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- Record sourced from PubMed, PMID 33533113.
- Also identified by DOI 10.1002/adma.202006089.
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Abstract
The synthesis of fully epitaxial ferroelectric Hf<sub>0.5</sub> Zr<sub>0.5</sub> O<sub>2</sub> (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 Pb<sub>2</sub> Ir<sub>2</sub> O<sub>7</sub> (PIO) and Bi<sub>2</sub> Ru<sub>2</sub> O<sub>7</sub> (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.