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Computational prediction of novel MAB phases
Linköping University, Department of Physics, Chemistry and Biology, Materials design. Linköping University, Faculty of Science & Engineering.ORCID iD: 0000-0001-5973-0065
2022 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The synthesis procedure of any materials system is often considered a challenging task if performed without any prior knowledge. Theoretical models may thus be used as an external input and guide experimental efforts toward novel exotic materials which are most likely to be synthesizable. The aim of this work is to apply theoretical models and develop frameworks for reliable predictions of thermodynamically stable materials. The material in focus herein is the family of atomic layered boride-based materials referred to as MAB phases.

The ground state energy of a material system may be obtained by applying firstprincipal calculations, such as density functional theory (DFT), which has thoroughly been used throughout this thesis. However, performing modern state-of-the-art quantum mechanical calculations, in general, relies on a pre-defined crystal structure which may be constructed based on an a priori known structure or obtained through the use of crystal structure prediction models. In this work, both approaches are explored. We herein perform a thermodynamical screening study to predict novel stable ternary boron-based materials by considering M2AB2, M3AB4, M4AB6, MAB and M4AB4 compositions in orthorhombic and hexagonal symmetries with inspiration from experimentally synthesized MAB phases. The considered atomic elements are M = Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Fe, Co, A = Al, Ga, In, and B is boron. Among the considered compounds, seven experimentally synthesized phases are verified as stable, and we predict the three hypothetical phases to be stable - Hf2InB2, Zr2InB2, and Mo4AlB4. Additionally, 23 phases of varying symmetries and compositions are predicted as close to stable or to be metastable.

However, the assumption of assigning initial crystal structures based on neighbouring compounds may drastically limit the outcome of a screening study. State-of-the-art techniques to generate low energy crystal structures within the considered material phase space is thus explored. More specifically, the Mo-Sc-Al-B system is studied along the ternary joints of (MoxSc1-x)2AlB2 where 0 < x < 1 by using the cluster expansion (CE) and the crystal structure prediction (CSP) codes, CLEASE and USPEX, in analogy. Previous attempts to study the Mo-Sc-Al-B system has been limited by only considering either hexagonal or orthorhombic symmetries. We challenge such approaches by covering larger portions of the phase space efficiently by combining CSP and CE frameworks. The Mo4/3Sc2/3AlB2 (R ̅3m) phase, previously referred to as i-MAB, is verified stable in addition to Mo2/3Sc4/3AlB2 (R3).

The suggested approach of combining CE and CSP frameworks for investigating multi-component systems consists of initially performing CSP searches on the systems of smaller order constituting the system in focus. In the pseudo-ternary (MoxSc1-x)2AlB2 system, this refers to performing CSP searches on the ternary Mo2AlB2 and Sc2AlB2 systems. In addition, we also consider the structures of experimentally known phases with similar compositions. The complete set of structures obtained either from CSP or public databases, was later used to design CE models where mixing tendencies in addition to stability determined which model to further study. The predicted low-energy structures of the CE model were relaxed and used as seed structures within a complete CSP search covering the (MoxSc1-x)2AlB2 system for 0 < x < 1. We demonstrate that the use of seed structures, obtained from CE models, efficiently improved the search for low-energy structures within a multi-component system. The suggested approach is yet to be tested on any other system but is applicable to any alternative multi-component system.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2022. , p. 45
Series
Linköping Studies in Science and Technology. Licentiate Thesis, ISSN 0280-7971 ; 1939
National Category
Materials Chemistry
Identifiers
URN: urn:nbn:se:liu:diva-185703DOI: 10.3384/9789179293819ISBN: 9789179293802 (print)ISBN: 9789179293819 (electronic)OAI: oai:DiVA.org:liu-185703DiVA, id: diva2:1666844
Presentation
2022-06-17, Online through Zoom (contact henrietta.winslow@liu.se) and Nobel BL32, B Building, Campus Valla, Linköping, 13:15 (Swedish)
Opponent
Supervisors
Available from: 2022-06-09 Created: 2022-06-09 Last updated: 2022-06-09Bibliographically approved
List of papers
1. Theoretical predictions of phase stability for orthorhombic and hexagonal ternary MAB phases
Open this publication in new window or tab >>Theoretical predictions of phase stability for orthorhombic and hexagonal ternary MAB phases
2022 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 24, no 18, p. 11249-11258Article in journal (Refereed) Published
Abstract [en]

In the quest for finding novel thermodynamically stable, layered, MAB phases promising for synthesis, we herein explore the phase stability of ternary MAB phases by considering both orthorhombic and hexagonal crystal symmetries for various compositions (MAB, M2AB2, M3AB4, M4AB4, and M4AB6 where M = Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Fe, and Co, A = Al, Ga, and In, and B is boron). The thermodynamic stability of seven previously synthesized MAB phases is confirmed, three additional phases are predicted to be stable, and 23 phases are found to be close to stable. Furthermore, the crystal symmetry preference for forming orthorhombic or hexagonal crystal structures is investigated where the considered Al-based MAB phases tend to favour orthorhombic structures whereas Ga- and In-based phases in general prefer hexagonal structures. The theoretically predicted stable MAB phases along with the structural preference is intended to both guide experimental efforts and to give an insight into the stability for different crystal symmetries of MAB phases.

Place, publisher, year, edition, pages
Cambridge, United Kingdom: Royal Society of Chemistry, 2022
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:liu:diva-184837 (URN)10.1039/d1cp05750b (DOI)000788174800001 ()35481473 (PubMedID)
Note

Funding Agencies|Swedish Research Council, European Commission [2019-05047, 2018-05973]; Knut & Alice Wallenberg Foundation [KAW 2020.0033]

Available from: 2022-05-12 Created: 2022-05-12 Last updated: 2024-02-02Bibliographically approved

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Carlsson, Adam

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