A combined DFT and NPD approach to determine the structure and composition of the ε-phase of tungsten boride

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dc.contributor.authorSetayandeh, SSen_AU
dc.contributor.authorStansby, JHen_AU
dc.contributor.authorObbard, EGen_AU
dc.contributor.authorBrand, MIen_AU
dc.contributor.authorMiskovic, DMen_AU
dc.contributor.authorLaws, KJen_AU
dc.contributor.authorPeterson, VKen_AU
dc.contributor.authorAstbury, JOen_AU
dc.contributor.authorWilson, CLen_AU
dc.contributor.authorIrukuvarghula, Sen_AU
dc.contributor.authorBurr, PAen_AU
dc.date.accessioned2024-11-15T02:40:26Zen_AU
dc.date.available2024-11-15T02:40:26Zen_AU
dc.date.issued2023-10-15en_AU
dc.date.statistics2024-11-08en_AU
dc.description.abstractThe ε-phase of tungsten boride, conventionally labelled as W2B5, has been identified as a promising candidate for shielding application in spherical tokamak fusion reactors. However, further research has been hindered by a lack of agreement on the structure and even composition of the ε-phase. Here, we identify the stable crystal structure and stoichiometry range of ε tungsten borides through a combination of ab initio simulations and neutron diffraction of isotopically enriched samples. We considered the ability to accommodate hypo-stoichiometry in six published structures of the ε phase. Chemical disorder was modelled using configurational ensembles to account for entropy of non-stoichiometry. We show that two W2B4-x structures (with x=∼0.25 − 0.5), with space group symmetry P63/mmc and P63/mcm, appear to be thermodynamically stable. These candidate compounds have 6.2 − 7.8 at.% less B than the W2B5 composition reported in exiting phase diagrams. We confirm these findings by means of neutron powder diffraction, performed on 11B-enriched arc-melted and crushed samples. Rietveld refinement using the neutron data shows the ε-phase to be better described as W2B3.60(2) (P63/mcm), in keeping with density functional theory (DFT) calculations. Linear change in DFT-derived lattice parameters of the candidates for the ε-phase proposes a simple model to assess the tungsten boride composition by measuring the lattice parameter (e.g. by X-ray diffraction. The simulations also reveal that the material can accommodate a range of stoichiometric variations (via B vacancies) with relatively small stored energy, which is a desirable feature for neutron shielding application. © 2023 The Authors. Published by Elsevier Ltd on behalf of Acta Materialia Inc. Open Access CC-NC-NDen_AU
dc.description.sponsorshipSSS, PAB, MIB, JHS and EGO would like to acknowledge Tokamak Energy (UK) for providing financial support. MB acknowledges Tyree foundation for providing financial support. This research was supported by an Australian Government Research Training Program (RTP) Scholarships. This work was undertaken with the assistance of resources and services from the National Computational Infrastructure (NCI), which is supported by the Australian Government; the Pawsey Supercomputing Centre, which is supported by the Australian Government and the Government of Western Australia; and was enabled by Intersect Australia Limited (www.intersect.org.au). Part of this research was undertaken on the Echidna beamline at the Australian Centre for Neutron Scattering, ANSTO, under proposal MI13195.en_AU
dc.identifier.articlenumber119282en_AU
dc.identifier.citationSetayandeh, S. S., Stansby, J. H., Obbard, E. G., Brand, M. I., Miskovic, D. M., Laws, K. J., Peterson, V. K., Astbury, J. O., Wilson, C. L., Irukuvarghula, S., & Burr, P. A. (2023). A combined DFT and NPD approach to determine the structure and composition of the ε-phase of tungsten boride. Acta Materialia, 259, 119282. doi:10.1016/j.actamat.2023.119282en_AU
dc.identifier.issn1359-6454en_AU
dc.identifier.journaltitleActa Materialiaen_AU
dc.identifier.urihttps://doi.org/10.1016/j.actamat.2023.119282en_AU
dc.identifier.urihttps://apo.ansto.gov.au/handle/10238/15751en_AU
dc.identifier.volume259en_AU
dc.languageEnglishen_AU
dc.language.isoenen_AU
dc.publisherElsevieren_AU
dc.subjectTungstenen_AU
dc.subjectBoridesen_AU
dc.subjectReactorsen_AU
dc.subjectCrystal structureen_AU
dc.subjectStoichiometryen_AU
dc.subjectNeutron diffractionen_AU
dc.subjectDensity functional methoden_AU
dc.subjectPhase diagramsen_AU
dc.subjectX-ray diffractionen_AU
dc.titleA combined DFT and NPD approach to determine the structure and composition of the ε-phase of tungsten borideen_AU
dc.typeJournal Articleen_AU
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