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Pressure-induced magnetovolume effect in CoCrFeAl high-entropy alloy
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.ORCID iD: 0000-0003-2832-3293
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
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2019 (English)In: Communications Physics, E-ISSN 2399-3650, Vol. 2, article id 42Article in journal (Refereed) Published
Abstract [en]

High-entropy alloys (HEAs) composed of multiple-principal elements with (nearly) equimolar ratio establish a new conceptual framework for alloy design and hold a promise for extensive applications in industry, akin to the controlled expansion alloys (CEAs), such as Invar alloys. Spontaneously, one question emerges - would it be possible to synthesize a novel class of alloys combining the virtues of both CEAs and HEAs? Here, we report the pressure-induced magnetovolume effect in the body-centered-cubic CoCrFeAl HEA coupled with magnetic phase transitions from ferromagnetic to paramagnetic, and to non-magnetic states, originating from the successive collapses of local magnetic moments of Co and Fe. The observed magnetovolume anomalies, occurring in a progressive way, tailor appreciably the coefficient of thermal expansion of CoCrFeAl. These results further strengthen HEAs’ anticipated potential for designing multifunctional materials in virtue of their multiple outstanding properties, and reveal possible routes for their future synthesis.

Place, publisher, year, edition, pages
2019. Vol. 2, article id 42
National Category
Condensed Matter Physics Earth and Related Environmental Sciences
Identifiers
URN: urn:nbn:se:uu:diva-382796DOI: 10.1038/s42005-019-0141-9ISI: 000467220700001OAI: oai:DiVA.org:uu-382796DiVA, id: diva2:1313377
Available from: 2019-05-03 Created: 2019-05-03 Last updated: 2019-11-25Bibliographically approved
In thesis
1. Synthesis and Tuning of Multifunctional Materials at High Pressure
Open this publication in new window or tab >>Synthesis and Tuning of Multifunctional Materials at High Pressure
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

At the present stage, human society is developing at an unprecedented speed, facing an emergence of highly pressing challenges, e.g., information explosion, energy production problems, environmental pollution, climate problems. Functional materials with tailored properties are considered as holding a key to solving these problems. In this thesis, high-pressure techniques were employed to synthesize and tune the properties of multiferroic materials relevant to spintronic and light-harvesting applications, and multifunctional high-entropy alloys.

Melanostibite (Mn2FeSbO6, MFSO) is a very rare mineral discovered in Sweden. Previous studies indicate it is a potential multiferroic material with foreseen applications in information storage and spintronic devices. However, its multiferroic phase has not been synthesized yet. Herein, the structural evolution of MFSO was studied up to ~50 GPa, and the LiNbO3-type MFSO was synthesized at high pressure and moderate temperature. As a polar structure material, the LiNbO3-type MFSO represents a promising candidate for multiferroic materials. The double perovskite, Pb2CoTeO6, was also compressed to ~60 GPa, while no polar phase was discovered. The obtained results provide guidance to the synthesis of new multiferroic double perovskite.

Solar energy is a promising alternative to fossil fuels and thus a viable solution to the global energy problem. Light-harvesting materials, which absorb sunlight and transform it into electricity by the photovoltaic effect, represent the core part of solar cells. Currently, the dominant commercial light-harvesting material is silicon. However, silicon and recently emerged organic-inorganic perovskites have several drawbacks. Multiferroic oxides are considered as stable and nontoxic light-harvesting materials. But, their bandgap energies are generally too large for photovoltaic applications. Herein, high-pressure technique was applied to treat Mn3TeO6, and a quenchable phase of Mn3TeO6 displaying a greatly narrowed bandgap was synthesized. The measured absorption spectrum of the quenched phase reveals that it may be suitable for photovoltaic applications. The present research opens a green way to tune the bandgap energy of multiferroic.

High-entropy alloys (HEAs) were first synthesized in 2004. However, knowledge of this new class of promising alloys is still very limited, even in very fundamental aspects. The present results reveal that lattice distortion plays important roles in the phase transition of HEAs, and demonstrate the future possibility of designing the Invar high-entropy alloy, a promising structural material. The results show that it is possible to combine several practical properties in a single alloy, which will widen the range of applications of HEAs. 

The presented research demonstrates that high-pressure represents an effective way to tune various properties of materials, as well as can be applied for the synthesis of materials with exotic properties which are usually not stable or attainable at ambient conditions.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2020. p. 71
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1883
Keywords
double perovskite, multiferroic, bandgap engineering, high-entropy alloy, high pressure
National Category
Geosciences, Multidisciplinary
Research subject
Earth Science with specialization in Mineral Chemistry, Petrology and Tectonics
Identifiers
urn:nbn:se:uu:diva-397718 (URN)978-91-513-0825-8 (ISBN)
Public defence
2020-01-28, Axel Hambergsalen, Geocentrum, Villavägen 16, Uppsala, 10:00 (English)
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Available from: 2019-12-19 Created: 2019-11-25 Last updated: 2020-01-14

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Liu, LeiVitos, LeventeDong, MinjieAlmqvist, Bjarne S.G.Ivanov, SergeyRubensson, Jan-ErikLazor, Peter

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