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Kinetically stabilized ferroelectricity in bulk single-crystalline HfO2:Y

Abstract

HfO2, a simple binary oxide, exhibits ultra-scalable ferroelectricity integrable into silicon technology. This material has a polymorphic nature, with the polar orthorhombic (Pbc21) form in ultrathin films regarded as the plausible cause of ferroelectricity but thought not to be attainable in bulk crystals. Here, using a state-of-the-art laser-diode-heated floating zone technique, we report the Pbc21 phase and ferroelectricity in bulk single-crystalline HfO2:Y as well as the presence of the antipolar Pbca phase at different Y concentrations. Neutron diffraction and atomic imaging demonstrate (anti)polar crystallographic signatures and abundant 90°/180° ferroelectric domains in addition to switchable polarization with negligible wake-up effects. Density-functional-theory calculations indicate that the yttrium doping and rapid cooling are the key factors for stabilization of the desired phase in bulk. Our observations provide insights into the polymorphic nature and phase control of HfO2, remove the upper size limit for ferroelectricity and suggest directions towards next-generation ferroelectric devices.

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Fig. 1: Single crystals and phase diagram of HfO2:Y.
Fig. 2: Neutron diffraction studies reveal o-FE phase of the 12% HfO2:Y single crystal.
Fig. 3: Ferroelectric domains and PE loop in 12% HfO2:Y.
Fig. 4: Energy landscape and barriers of representative transformation paths from DFT calculations.

Data availability

Source data for the main paper figures are provided with this paper. Additional data are available from the corresponding authors upon request.

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Acknowledgements

The experimental work was performed at the Centre for Quantum Materials Synthesis (cQMS), funded by the Gordon and Betty Moore Foundation’s EPiQS initiative through grant no. GBMF6402, and by Rutgers University. Neutron diffraction studies used resources at the Spallation Neutron Source, a Department of Energy Office of Science User Facility operated by the ORNL. We thank Q. Zhang from the ORNL for support with neutron diffraction measurements. Y.Q., S.S. and K.M.R. were supported by the Office of Naval Research (grant no. N00014-17-1-2770). The DFT calculations performed for this study used the resources provided by the High-Performance Computing Modernization Office of the Department of Defense and the Rutgers University Parallel Computing clusters.

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Authors and Affiliations

Authors

Contributions

X.X. and S.-W.C. conceived the idea. X.X. synthesized the single crystals, collected the XRD data and tested the ferroelectric properties. F.-T.H. took the optical microscope pictures and conducted the TEM experiments. Y.Q., S.S. and K.M.R. performed the DFT calculations. D.O. and J.Y. carried out the neutron diffraction experiments and refinement. F.-T.H. and M.-W.C performed the STEM experiments. X.X., F.-T.H., Y.Q., S.S., K.M.R. and S.-W.C. wrote the manuscript.

Corresponding author

Correspondence to Sang-Wook Cheong.

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Peer review information Nature Materials thanks Thomas Mikolajick and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–11, Discussion, Methods, Table 1 and refs. 1–6.

Source data

Source Data Fig. 1

Source data of XRD.

Source Data Fig. 2

Source data of NPD.

Source Data Fig. 3

Source data of P–E loop.

Source Data Fig. 4

Source data of DFT energy landscape.

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Xu, X., Huang, FT., Qi, Y. et al. Kinetically stabilized ferroelectricity in bulk single-crystalline HfO2:Y. Nat. Mater. 20, 826–832 (2021). https://doi.org/10.1038/s41563-020-00897-x

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