A Critical Strain Window for Stabilizing Polar Orthorhombic Hf<sub>0</sub>.<sub>5</sub>Zr<sub>0</sub>.<sub>5</sub>O<sub>2</sub> Epitaxial Thin Films with Scale-Free Domain Walls.
basic_science · Level V
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- Record sourced from PubMed, PMID 41527284.
- Also identified by DOI 10.1002/adma.202521362.
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Abstract
Ferroelectric (Hf, Zr)O<sub>2</sub> (HZO) films are well positioned to revolutionize the next-generation memories and neuromorphic computing, though metastability of their polar orthorhombic phase remains a daunting challenge. Here, we demonstrate that the phase structure of epitaxial HZO films can be effectively tuned on yttria-stabilized-zirconia (YSZ) substrate, resulting in tetragonal, orthorhombic, and monoclinic phases with distinct strain states modulated by film thickness. A critical strain window (+1.16% < ε<sub>yy</sub> < +2.30%) is identified to stabilize the polar orthorhombic phase, outside of which tetragonal or monoclinic phase emerges. Tetragonal-orthorhombic phase transition is observed from lattice relaxation, confirming that the phase structure of HZO is governed by strain. 90° nanoscale domains with interleaved yet atomically sharp domain walls are also revealed, rendering direct experimental evidence for scale-free ferroelectricity. Our findings not only establish critical conditions for stable polar orthorhombic HZO, but also shed new insight into unconventional scaling of ferroelectric fluorite oxides.