Compositional pathways and anisotropic thermal expansion of high-entropy transition metal diborides |
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| Affiliation: | 1. National Research Council of Italy, Institute of Science and Technology for Ceramics, Faenza, 48018 RA, Italy;2. Elettra - Sincrotrone Trieste S.C.p.A., Strada Statale 14 - Km 163, 5 in AREA Science Park, 34149, Basovizza, Trieste, Italy;1. School of Electron-Mechanical Engineering, Guangdong University of Technology, Guangzhou 51006, China;2. Department of Materials Science and Engineering, University of Sheffield, Sheffield S1 3JD, UK;3. School of Chemical Engineering and Light Industry, Guangdong University of Technology, Guangzhou 510006, China;4. The Henry Royce Institute, Sir Robert Hadfield Building, Sheffield S1 3JD, UK;1. National Research Council of Italy, Institute of Science and Technology for Ceramics, Faenza, 48018 RA, Italy;2. Elettra - Sincrotrone Trieste S.C.p.A., Strada Statale 14 - Km 163, 5 in AREA Science Park, 34149 Basovizza, Trieste, Italy;1. Dipartimento di Ingegneria Meccanica, Chimica, e dei Materiali, Unità di Ricerca del Consorzio Interuniversitario Nazionale per la Scienza e Tecnologia dei Materiali (INSTM), Università degli Studi di Cagliari, via Marengo 2, 09123 Cagliari, Italy;2. Dipartimento di Chimica e Farmacia, Università degli Studi di Sassari, Via Vienna 2, 07100 Sassari, Italy;3. International Research Centre in Critical Raw Materials-ICCRAM, University of Burgos, Plaza Misael Bañuelos s/n, 09001 Burgos, Spain;1. Department of Physics and Astronomy, University of California, Irvine, CA, 92697, USA;2. Department of NanoEngineering, Program of Materials Science and Engineering, University of California, San Diego, La Jolla, CA, 92093, USA;3. Department of Materials Science and Engineering, University of California, Irvine, CA, 92697, USA;4. Department of Mechanical and Aerospace Engineering, University of California, Irvine, CA, 92697, USA;5. Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, NY, 11973, USA |
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| Abstract: | The recent discovery of high entropy transition metal diborides (HEBs) has sparked renewed interest in ultra-high temperature ceramics (UHTCs). Presently, transition metal (Me) oxides based boro-carbo/thermal reduction (BCTR) syntheses show great promise as relatively cheap production methods, but also may present limits to attain single phase pure HEBs. Herein, by selectively tuning the concentration of boron and carbon, the reducing agents of Me oxide mixture (Me = Ti, Ta, Nb, Zr and Hf), and exploiting high-resolution synchrotron X-ray powder diffraction, we first identified and quantified the formation of intermediate phases during the BCTR synthesis, with the ultimate intent to achieve a full dense (Ti,Ta,Nb,Zr,Hf)B2 solid solution (SS). Additional insight was obtained by temperature dependent diffraction, which highlighted, for the first time in this class of materials, anisotropic thermal expansion, most likely at the origin of the SS micro-cracking, as was also observed by electron microscopy. |
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| Keywords: | High entropy borides Solid state powder synthesis Synchrotron radiation x-ray diffraction Electron microscopy Anisotropic thermal expansion |
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