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Stability trends of MAX phases from first principles
Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.ORCID-id: 0000-0001-5036-2833
Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
2010 (Engelska)Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 81, nr 22, s. 220102-Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

We have developed a systematic method to investigate the phase stability of M(n+1)AX(n) phases, here applied for M=Sc, Ti, V, Cr, or Mn, A=Al, and X=C or N. Through a linear optimization procedure including all known competing phases, we identify the set of most competitive phases for n=1-3 in each system. Our calculations completely reproduce experimental occurrences of stable MAX phases. We also identify and suggest an explanation for the trend in stability as the transition metal is changed across the 3d series for both carbon- and nitrogen-based systems. Based on our results, the method can be used to predict stability of potentially existing undiscovered phases.

Ort, förlag, år, upplaga, sidor
American Physical Society , 2010. Vol. 81, nr 22, s. 220102-
Nationell ämneskategori
Teknik och teknologier
Identifikatorer
URN: urn:nbn:se:liu:diva-58288DOI: 10.1103/PhysRevB.81.220102ISI: 000279147000001OAI: oai:DiVA.org:liu-58288DiVA, id: diva2:337908
Anmärkning
Original Publication: Martin Dahlqvist, Björn Alling and Johanna Rosén, Stability trends of MAX phases from first principles, 2010, Physical Review B. Condensed Matter and Materials Physics, (81), 22, 220102. http://dx.doi.org/10.1103/PhysRevB.81.220102 Copyright: American Physical Society http://www.aps.org/ Tillgänglig från: 2010-08-10 Skapad: 2010-08-09 Senast uppdaterad: 2017-12-12
Ingår i avhandling
1. Materials Design from First Principles: stability and magnetism of nanolaminates
Öppna denna publikation i ny flik eller fönster >>Materials Design from First Principles: stability and magnetism of nanolaminates
2014 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

In this thesis, first-principles calculations within density functional theory are presented, with a principal goal to investigate the phase stability of so called Mn+1AXn (MAX) phases. MAX phases are a group of nanolaminated materials comprised of a transition metal (M), a group 12-16 element (A), and carbon or nitrogen (X). They combine ceramic and metallic characteristics, and phase stability studies are motivated by a search for new phases with novel properties, such as magnetism, and for the results to be used as guidance in attempted materials synthesis in the lab.

To investigate phase stability of a hypothetical material, a theoretical approach has been developed, where the essential part is to identify the set of most competing phases relative to the material of interest. This approach advance beyond more traditional evaluation of stability, where the energy of formation of the material is generally calculated relative to its single elements, or to a set of ad hoc chosen competing phases. For phase stability predictions to be reliable, validation of previous experimental work is a requirement prior to investigations of new, still hypothetical, materials. It is found that the predictions from the developed theoretical approach are consistent with experimental observations for a large set of MAX phases. The predictive power is thereafter demonstrated for the new phases Nb2GeC and Mn2GaC, which subsequently have been synthesized as thin films. It should be noted that Mn is used for the first time as sole M-element in a MAX phase. Hence, the theory is successfully used to find new candidates, and to guide experimentalists in their work on novel promising materials. Phase stability is also evaluated for MAX phase alloys. Incorporation of oxygen in different M2AlC phases are studied, and the results show that oxygen prefer different sites depending on M-element, through the number of available non-bonding M d-electrons. The theory also predicts that oxygen substituting for carbon in Ti2AlC stabilizes the material, which explains the  experimentally observed 12.5 at% oxygen (x = 0.5) in Ti2Al(C1-xOx).

Magnetism is a recently attained property of MAX phase materials, and a direct result of this Thesis work. We have demonstrated the importance of choice of magnetic spin configuration and electron correlations approximations for theoretical evaluation of the magnetic ground state of Cr2AC (A = Al, Ga, Ge). Furthermore, alloying Cr2AlC with Mn to obtain the first magnetic MAX phase have been theoretically predicted and experimentally verified. Using Mn2GaC as model system, Heisenberg Monte Carlo simulations have been used to explore also noncollinear magnetism, suggesting a large set of possible spin configurations (spin waves and spin spirals) to be further investigated in future theoretical and experimental work.

Ort, förlag, år, upplaga, sidor
Linköping: Linköping University Electronic Press, 2014. s. 81
Serie
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1571
Nationell ämneskategori
Naturvetenskap
Identifikatorer
urn:nbn:se:liu:diva-104764 (URN)10.3384/diss.diva-104764 (DOI)978-91-7519-411-0 (ISBN)
Disputation
2014-03-14, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 09:15 (Engelska)
Opponent
Handledare
Tillgänglig från: 2014-02-25 Skapad: 2014-02-25 Senast uppdaterad: 2019-11-19Bibliografiskt granskad

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