Ferroelectricity in Hafnia: The Origin of Nanoscale Stabilization

Ferroelectricity in Hafnia: The Origin of Nanoscale Stabilization | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Physical Sciences - Article Ferroelectricity in Hafnia: The Origin of Nanoscale Stabilization Xiaoshan Xu, Xin Li, Guodong Ren, Haidong Lu, Kartik Samanta, and 11 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4739777/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract The discovery of ferroelectric properties in hafnia-based materials have boosted the potential of incorporating ferroelectricity in advanced electronics, thanks to their compatibility with silicon technology. However, comprehending why these materials defy the common trend of reduced ferroelectric ordering at the nanoscale, and the mechanism that stabilizes the ferroelectric phase—which is absent in hafnia’s phase diagram—presents significant challenges to our traditional knowledge of ferroelectricity. In this work, we show that the formation of the orthorhombic ferroelectric phase ( o-FE , space group Pca2 1 ) of the single-crystalline epitaxial films of 10% La-doped HfO 2 (LHO) on (111)-oriented yttria stabilized zirconia (YSZ) relies on the stability of the orthorhombic antiferroelectric phase ( o-AFE , space group Pbca) that is present in the high-pressure region of the phase diagram of hafnia. Our detailed x-ray diffraction studies, electron microscopy, and neutron diffraction measurements demonstrate that as-grown LHO films structurally represent an orthorhombic phase that is largely composed of the o-AFE phase being thermodynamically stabilized by the compressive strain imposed by the substrate on the lattice of hafnia stretched by La doping. As follows from our Kelvin probe force microscopy studies, under mechanical poling, the o-AFE phase is converted to the o-FE phase which remains stable under ambient conditions. We find that the orthorhombic phase stability is enhanced with decreasing film thickness down to one unit cell¾a trend that is unknown in any other ultrathin ferroelectric films. This is due to the vanishing depolarization field of the o-AFE phase and the isomorphic LHO/YSZ interface, supporting strain-enhanced ferroelectricity in the ultrathin films down to the single-unit-cell thickness, as evident from our electron microscopy and reflection high energy electron diffraction studies. This results in an unprecedented increase of the Curie temperature up to 850 °C—the highest reported for sub-nanometer-thick ferroelectrics. Overall, our findings unveil two long-standing mysteries of ferroelectric hafnia—the stability of the o-FE phase and its enhancement at the nanoscale, opening the way for advanced engineering of hafnia-based materials for ferroelectric applications and heralding a new frontier of high-temperature ferroelectrics at the two-dimensional limit. Physical sciences/Materials science/Materials for devices/Information storage Physical sciences/Materials science/Nanoscale materials/Structural properties Full Text Additional Declarations There is NO Competing Interest. Supplementary Files 20240713supplementarymaterialsfinal.docx Supplementary information Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4739777","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Physical Sciences - Article","associatedPublications":[],"authors":[{"id":329770854,"identity":"6304d6ec-7931-4300-b58a-d8a903a9de9d","order_by":0,"name":"Xiaoshan 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20:50:14","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4739777/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4739777/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":75427593,"identity":"b902d8c9-0c72-4a8d-9d5c-050d5b606a5e","added_by":"auto","created_at":"2025-02-04 12:28:45","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1196330,"visible":true,"origin":"","legend":"","description":"","filename":"20240714LHOEpisubmit.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4739777/v1_covered_f344289c-ee24-41c9-b078-9e83455e97f5.pdf"},{"id":60865522,"identity":"2c74fed2-a279-40a1-bd69-94dd23815a52","added_by":"auto","created_at":"2024-07-23 03:11:53","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":35187601,"visible":true,"origin":"","legend":"Supplementary 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Stabilization","fulltext":[],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":false,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":true,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":true,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-4739777/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4739777/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe discovery of ferroelectric properties in hafnia-based materials have boosted the potential of incorporating ferroelectricity in advanced electronics, thanks to their compatibility with silicon technology. However, comprehending why these materials defy the common trend of reduced \u0026nbsp;ferroelectric ordering at the nanoscale, and the mechanism that stabilizes the ferroelectric phase—which is absent in hafnia’s phase diagram—presents significant challenges to our traditional knowledge of ferroelectricity. In this work, we show that the formation of the orthorhombic ferroelectric phase (\u003cem\u003eo-FE\u003c/em\u003e, space group Pca2\u003csub\u003e1\u003c/sub\u003e) of the single-crystalline epitaxial films of 10% La-doped HfO\u003csub\u003e2\u003c/sub\u003e (LHO) on (111)-oriented yttria stabilized zirconia (YSZ) relies on the stability of the orthorhombic antiferroelectric phase (\u003cem\u003eo-AFE\u003c/em\u003e, space group Pbca) that is present in the high-pressure region of the phase diagram of hafnia. Our detailed x-ray diffraction studies, electron microscopy, and neutron diffraction measurements demonstrate that as-grown LHO films structurally represent an orthorhombic phase that is largely composed of the \u003cem\u003eo-AFE\u003c/em\u003e phase being thermodynamically stabilized by the compressive strain imposed by the substrate on the lattice of hafnia stretched by La doping. As follows from our Kelvin probe force microscopy studies, under mechanical poling, the \u003cem\u003eo-AFE\u003c/em\u003e phase is converted to the \u003cem\u003eo-FE\u003c/em\u003e phase which remains stable under ambient conditions. We find that the orthorhombic phase stability is enhanced with decreasing film thickness down to one unit cell¾a trend that is unknown in any other ultrathin ferroelectric films. This is due to the vanishing depolarization field of the \u003cem\u003eo-AFE\u003c/em\u003e phase and the isomorphic LHO/YSZ interface, supporting strain-enhanced ferroelectricity in the ultrathin films down to the single-unit-cell thickness, as evident from our electron microscopy and reflection high energy electron diffraction studies. This results in an unprecedented increase of the Curie temperature up to 850 °C—the highest reported for sub-nanometer-thick ferroelectrics. Overall, our findings unveil two long-standing mysteries of ferroelectric hafnia—the stability of the \u003cem\u003eo-FE\u003c/em\u003e phase and its enhancement at the nanoscale, opening the way for advanced engineering of hafnia-based materials for ferroelectric applications and heralding a new frontier of high-temperature ferroelectrics at the two-dimensional limit.\u003c/p\u003e","manuscriptTitle":"Ferroelectricity in Hafnia: The Origin of Nanoscale Stabilization","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-07-23 03:11:48","doi":"10.21203/rs.3.rs-4739777/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"a440714f-a520-4731-87ca-6c22ff6f30be","owner":[],"postedDate":"July 23rd, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":34907228,"name":"Physical sciences/Materials science/Materials for devices/Information storage"},{"id":34907229,"name":"Physical sciences/Materials science/Nanoscale materials/Structural properties"}],"tags":[],"updatedAt":"2025-02-04T12:20:35+00:00","versionOfRecord":[],"versionCreatedAt":"2024-07-23 03:11:48","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4739777","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4739777","identity":"rs-4739777","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}