liu.seSearch for publications in DiVA
Change search
Refine search result
1 - 45 of 45
Cite
Citation style
• apa
• harvard1
• ieee
• modern-language-association-8th-edition
• vancouver
• oxford
• Other style
More styles
Language
• de-DE
• en-GB
• en-US
• fi-FI
• nn-NO
• nn-NB
• sv-SE
• Other locale
More languages
Output format
• html
• text
• asciidoc
• rtf
Rows per page
• 5
• 10
• 20
• 50
• 100
• 250
Sort
• Standard (Relevance)
• Author A-Ö
• Author Ö-A
• Title A-Ö
• Title Ö-A
• Publication type A-Ö
• Publication type Ö-A
• Issued (Oldest first)
• Created (Oldest first)
• Last updated (Oldest first)
• Disputation date (earliest first)
• Disputation date (latest first)
• Standard (Relevance)
• Author A-Ö
• Author Ö-A
• Title A-Ö
• Title Ö-A
• Publication type A-Ö
• Publication type Ö-A
• Issued (Oldest first)
• Created (Oldest first)
• Last updated (Oldest first)
• Disputation date (earliest first)
• Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
• 1.
Drexel University, PA 19104 USA; Drexel University, PA 19104 USA.
Experimental and theoretical characterization of ordered MAX phases Mo2TiAlC2 and Mo2Ti2AlC32015In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 118, no 9, p. 094304-Article in journal (Refereed)

Herein, we report on the phase stabilities and crystal structures of two newly discovered ordered, quaternary MAX phases-Mo2TiAlC2 and Mo2Ti2AlC3-synthesized by mixing and heating different elemental powder mixtures of mMo:(3-m) Ti:1.1Al:2C with 1.5 less than= m less than= 2.2 and 2Mo: 2Ti:1.1Al:2.7C to 1600 degrees C for 4 h under Ar flow. In general, for m greater than= 2 an ordered 312 phase, (Mo2Ti) AlC2, was the majority phase; for mless than 2, an ordered 413 phase (Mo2Ti2)AlC3, was the major product. The actual chemistries determined from X-ray photoelectron spectroscopy (XPS) are Mo2TiAlC1.7 and Mo2Ti1.9Al0.9C2.5, respectively. High resolution scanning transmission microscopy, XPS and Rietveld analysis of powder X-ray diffraction confirmed the general ordered stacking sequence to be Mo-Ti-Mo-Al-Mo-Ti-Mo for Mo2TiAlC2 and Mo-Ti-Ti-Mo-Al-Mo-Ti-Ti-Mo for Mo2Ti2AlC3, with the carbon atoms occupying the octahedral sites between the transition metal layers. Consistent with the experimental results, the theoretical calculations clearly show that M layer ordering is mostly driven by the high penalty paid in energy by having the Mo atoms surrounded by C in a face-centered configuration, i.e., in the center of the Mn+1Xn blocks. At 331 GPa and 367 GPa, respectively, the Youngs moduli of the ordered Mo2TiAlC2 and Mo2Ti2AlC3 are predicted to be higher than those calculated for their ternary end members. Like most other MAX phases, because of the high density of states at the Fermi level, the resistivity measurement over 300 to 10K for both phases showed metallic behavior. (C) 2015 AIP Publishing LLC.

• 2.
Drexel Univ, PA 19104 USA; Drexel Univ, PA 19104 USA.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Nucl Res Ctr Negev, Israel. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Drexel Univ, PA 19104 USA. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Drexel Univ, PA 19104 USA. Drexel Univ, PA 19104 USA; Nucl Res Ctr Negev, Israel.
A Tungsten-Based Nanolaminated Ternary Carbide: (W,Ti)(4)C4-x2019In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 58, no 2, p. 1100-1106Article in journal (Refereed)

Nanolamellar transition metal carbides are gaining increasing interests because of the recent developments of their twodimensional (2D) derivatives and promising performance for a variety of applications from energy storage, catalysis to transparent conductive coatings, and medicine. To develop more novel 2D materials, new nanolaminated structures are needed. Here we report on a tungsten based nanolaminated ternary phase, (W,Ti)(4)C4-x, synthesized by an Al catalyzed reaction of W, Ti, and C powders at 1600 degrees C for 4 h, under flowing argon. X-ray and neutron diffraction, along with Z-contrast scanning transmission electron microscopy, were used to determine the atomic structure, ordering, and occupancies. This phase has a layered hexagonal structure (P6(3)/mmc) with lattice parameters, a = 3.00880(7) angstrom, and c = 19.5633(6) angstrom and a nominal chemistry of (W,Ti)(4)C4-x (actual chemistry, W2.1(1)Ti1.6(1)C2.6(1)). The structure is comprised of layers of pure W that are also twin planes with two adjacent atomic layers of mixed W and Ti, on either side. The use of Al as a catalyst for synthesizing otherwise difficult to make phases, could in turn lead to the discovery of a large family of nonstoichiometric ternary transition metal carbides, synthesized at relatively low temperatures and shorter times.

The full text will be freely available from 2020-01-04 16:13
• 3.
Katholieke Univ Leuven, Belgium.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Katholieke Univ Leuven, Belgium; SCK CEN, Belgium. Katholieke Univ Leuven, Belgium; SCK CEN, Belgium. Katholieke Univ Leuven, Belgium. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. SCK CEN, Belgium. Katholieke Univ Leuven, Belgium. Katholieke Univ Leuven, Belgium. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Theoretical Prediction and Synthesis of (Cr2/3Zr1/3)(2)AIC i-MAX Phase2018In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 57, no 11, p. 6237-6244Article in journal (Refereed)

Guided by predictive theory, a new compound with chemical composition (Cr2/3Zr1/3)(2)AlC was synthesized by hot pressing of Cr, ZrH2, Al, and C mixtures at 1300 degrees C. The crystal structure is monoclinic of space group C2/c and displays in-plane chemical order in the metal layers, a so-called i-MAX phase. Quantitative chemical composition analyses confirmed that the primary phase had a (Cr2/3Zr1/3)(2)AlC stoichiometry, with secondary Cr2AlC, AlZrC2, and ZrC phases and a small amount of Al-Cr intermetallics. A theoretical evaluation of the (Cr2/3Zr1/3)(2)AlC magnetic structure was performed, indicating an antiferromagnetic ground state. Also (Cr2/3Zr1/3)(2)AlC, of the same structure, was predicted to be stable.

• 4.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Materials Design from First Principles: stability and magnetism of nanolaminates2014Doctoral thesis, comprehensive summary (Other academic)

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.

1. Phase stability of Ti2AlC upon oxygen incorporation: A first-principles investigation
Open this publication in new window or tab >>Phase stability of Ti2AlC upon oxygen incorporation: A first-principles investigation
2010 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 81, no 2, p. 024111-1-024111-8Article in journal (Refereed) Published
##### Abstract [en]

The phase stability of Ti2AlC upon oxygen incorporation has been studied by means of first-principles calculations. Recent experimental observations of this so-called MAX phase (M = early transition metal, A = A-group element, and X = C or N) show that the characteristic nanolaminated structure is retained upon oxygen incorporation, with strong indications of O substituting for C. Therefore, a solid solution of C and O on the carbon sublattice has been simulated by the so-called special quasirandom structure method. Through a developed systematic approach, the enthalpy of formation of Ti2Al(C1−x,Ox) has been compared to all experimentally known competing phases, and has been found favorable for all C to O ratios at the composition of the MAX phase. A negative isostructural formation enthalpy has also been predicted for Ti2Al(C1−x,Ox). Altogether, the results indicate that a large amount of oxygen, at least up to x=0.75, might be present in the Ti2AlC MAX-phase structure without decomposition of the material into its competing phases. Furthermore, an effect of an increased oxygen content is a corresponding increase in the bulk modulus and a change in electronic properties. These results are of importance for further understanding and identification of possible composition range of the MAX-phase oxycarbide, and hence for the prospect of tuning the material properties by a varying incorporation of oxygen.

##### National Category
Physical Sciences
##### Identifiers
urn:nbn:se:liu:diva-53771 (URN)10.1103/PhysRevB.81.024111 (DOI)
Available from: 2010-02-09 Created: 2010-02-03 Last updated: 2017-12-12Bibliographically approved
2. Oxygen incorporation and defect formation in Ti2AlC, V2AlC and Cr2AlC from first-principles calculations
Open this publication in new window or tab >>Oxygen incorporation and defect formation in Ti2AlC, V2AlC and Cr2AlC from first-principles calculations
##### Abstract [en]

We have studied oxygen incorporation and defect formation in M2AlC (M = Ti, V, Cr) MAX phases using first principles calculations. Evaluating phase stability and electronic structure for different oxygen and/or vacancy configurations, we show that oxygen prefer different lattice sites depending on M-element, which can be correlated to the number of available non-bonding M d-electrons. The results show that oxygen substitutes for carbon in Ti2AlC, while forming an interstitial oxygen in the Al-layer for Cr2AlC. We also predict that oxygen incorporation in Ti2AlC stabilizes the material, which explains the experimentally observed 12.5 at% oxygen (x = 0.5) in Ti2Al(C1-xOx). Due to similar valence electron configuration of Ti2AlC and the hypothetical M2AlC (M =Zr, Hf), we also investigate if oxygen can be used to stabilize the latter MAX phases.

##### National Category
Physical Sciences
##### Identifiers
urn:nbn:se:liu:diva-104758 (URN)
Available from: 2014-02-25 Created: 2014-02-25 Last updated: 2017-11-03Bibliographically approved
3. Stability trends of MAX phases from first principles
Open this publication in new window or tab >>Stability trends of MAX phases from first principles
2010 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 81, no 22, p. 220102-Article in journal (Refereed) 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.

##### Place, publisher, year, edition, pages
American Physical Society, 2010
##### National Category
Engineering and Technology
##### Identifiers
urn:nbn:se:liu:diva-58288 (URN)10.1103/PhysRevB.81.220102 (DOI)000279147000001 ()
##### Note
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/ Available from: 2010-08-10 Created: 2010-08-09 Last updated: 2017-12-12
4. Discovery of the Ternary Nanolaminated Compound Nb2GeC by a Systematic Theoretical-Experimental Approach
Open this publication in new window or tab >>Discovery of the Ternary Nanolaminated Compound Nb2GeC by a Systematic Theoretical-Experimental Approach
2012 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 109, no 3, p. 035502-Article in journal (Refereed) Published
##### Abstract [en]

Since the advent of theoretical materials science some 60 years ago, there has been a drive to predict and design new materials in silicio. Mathematical optimization procedures to determine phase stability can be generally applicable to complex ternary or higher-order materials systems where the phase diagrams of the binary constituents are sufficiently known. Here, we employ a simplex-optimization procedure to predict new compounds in the ternary Nb-Ge-C system. Our theoretical results show that the hypothetical Nb2GeC is stable, and excludes all reasonably conceivable competing hypothetical phases. We verify the existence of the Nb2GeC phase by thin film synthesis using magnetron sputtering. This hexagonal nanolaminated phase has a and c lattice parameters of similar to 3.24 angstrom and 12.82 angstrom.

##### Place, publisher, year, edition, pages
American Physical Society, 2012
##### National Category
Engineering and Technology
##### Identifiers
urn:nbn:se:liu:diva-79981 (URN)10.1103/PhysRevLett.109.035502 (DOI)000306466900014 ()
##### Note

Funding Agencies|European Research Council under the European Community|258509|Swedish Research Council (V.R.)||Swedish Foundation for Strategic Research||Swedish Agency for Innovation Systems (VINNOVA) Excellence Center FunMat||

Available from: 2012-08-17 Created: 2012-08-17 Last updated: 2017-12-07
5. Correlation between magnetic state and bulk modulus of Cr2AlC
Open this publication in new window or tab >>Correlation between magnetic state and bulk modulus of Cr2AlC
2013 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 113, no 21Article in journal (Refereed) Published
##### Abstract [en]

The effect of magnetism on the bulk modulus (B0) of M2AlC (M  = Ti, V, and Cr) has been studied using first principles calculations. We find that it is possible to identify an energetically favorable magnetic Cr2AlC phase without using any adjustable parameter, such as the Hubbard U. Furthermore, we show that an in-plane spin polarized configuration has substantially lower B0 as compared to the non-magnetic model. The existences of local magnetic moments on Cr atoms considerably improve agreement between theory and experiment regarding trends in B0 for M2AlC phases.

##### Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2013
##### National Category
Engineering and Technology
##### Identifiers
urn:nbn:se:liu:diva-96430 (URN)10.1063/1.4808239 (DOI)000320674500104 ()
##### Note

Funding Agencies|European Research Council under the European Community|258509|Swedish Research Council (VR)|621-2012-4425621-2011-4417|

Available from: 2013-08-20 Created: 2013-08-19 Last updated: 2017-12-06
6. Magnetic ground state of Cr2AlC, Cr2GaC, and Cr2GeC from first-principles interplay of spin configurations and strong electrons correlation
Open this publication in new window or tab >>Magnetic ground state of Cr2AlC, Cr2GaC, and Cr2GeC from first-principles interplay of spin configurations and strong electrons correlation
##### Abstract [en]

We have studied the interplay between spin configuration and electron correlations approximations as well as their influence on calculated lattice parameters, magnetic moments, and bulk modulus of the nanolaminated MAX phase materials Cr2AlC, Cr2GaC, and Cr2GeC. By considering non-, ferro- and, and five different antiferromagnetic configurations, we show the importance of including a broad range of magnetic states in search for the ground state. Our calculations show that when electron correlation is treated on the level of the generalized gradient approximation or with an additional Hubbard U interaction term up to a value of 1 eV, the magnetic ground state of Cr2AC (A=Al, Ga, Ge) is in-plane antiferromagnetic with finite Cr local moments and calculated lattice parameters and bulk modulus close to experimentally reported values.

##### National Category
Natural Sciences
##### Identifiers
urn:nbn:se:liu:diva-104759 (URN)
Available from: 2014-02-25 Created: 2014-02-25 Last updated: 2017-11-03Bibliographically approved
7. Magnetic nanoscale laminates with tunable exchange coupling from first principles
Open this publication in new window or tab >>Magnetic nanoscale laminates with tunable exchange coupling from first principles
2011 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 84, no 22, p. 220403-Article in journal (Refereed) Published
##### Abstract [en]

The M(n+1)AX(n) (MAX) phases are nanolaminated compounds with a unique combination of metallic and ceramic properties, not yet including magnetism. We carry out a systematic theoretical study of potential magnetic MAX phases and predict the existence of stable magnetic (Cr(1-x)Mn(x))(2)AlC alloys. We show that in this system ferromagnetically ordered Mn layers are exchange coupled via nearly nonmagnetic Cr layers, forming an inherent structure of atomic-thin magnetic multilayers, and that the degree of disorder between Cr and Mn in the alloy can be used to tune the sign and magnitude of the coupling.

##### Place, publisher, year, edition, pages
American Physical Society, 2011
##### National Category
Engineering and Technology
##### Identifiers
urn:nbn:se:liu:diva-73313 (URN)10.1103/PhysRevB.84.220403 (DOI)297763300001 ()
Available from: 2012-01-03 Created: 2012-01-02 Last updated: 2017-12-08
8. A Nanolaminated Magnetic Phase: Mn2GaC
Open this publication in new window or tab >>A Nanolaminated Magnetic Phase: Mn2GaC
2014 (English)In: Materials Research Letters, ISSN 2166-3831, Vol. 2, no 2, p. 89-93Article in journal (Refereed) Published
##### Abstract [en]

Layered magnetic materials are fascinating from the point of view of fundamental science as well as applications. Discoveries such as giant magnetoresistance (GMR) in magnetic multilayers have revolutionized data storage and magnetic recording, and concurrently initiated the search for new layered magnetic materials. One group of inherently nanolaminated compounds are the so called Mn+1AXn (MAX) phases. Due to the large number of isostructural compositions, researchers are exploring the wide range of interesting properties, and not primarily functionalization through optimization of structural quality. Magnetic MAX phases have been discussed in the literature, though this is hitherto an unreported phenomenon. However, such materials would be highly interesting, based on the attractive and useful properties attained with layered magnetic materials to date. Here we present a new MAX phase, (Cr1–xMnx)2GeC, synthesized as thin film in heteroepitaxial form, showing single crystal material with unprecedented structural MAX phase quality. The material was identified using first-principles calculations to study stability of hypothetical MAX phases, in an eort to identify a potentially magnetic material. The theory predicts a variety of magnetic behavior depending on the Mn concentration and Cr/Mn atomic conguration within the sublattice. The analyzed thin films display a magnetic signal well above room temperature and with partly ferromagnetic ordering. These very promising results open up a field of new layered magnetic materials, with high potential for electronics and spintronics applications.

##### Place, publisher, year, edition, pages
Taylor & Francis, 2014
##### Keywords
MAX phases, sputtering, transmission electron microscopy (TEM), ab initio calculation
##### National Category
Natural Sciences
##### Identifiers
urn:nbn:se:liu:diva-77774 (URN)10.1080/21663831.2013.865105 (DOI)
##### Note

On the day of the defence date the status of this article was previous Manuscript. The original title of the Manuscript was Magnetic nanoscale laminates from first principles and thin film synthesis.

Available from: 2012-05-29 Created: 2012-05-29 Last updated: 2018-03-15Bibliographically approved
9. Complex magnetism in nanolaminated Mn2GaC
Open this publication in new window or tab >>Complex magnetism in nanolaminated Mn2GaC
##### Abstract [en]

We have used first-principles calculations and Heisenberg Monte Carlo simulations to search for the magnetic ground state of Mn2GaC, a recently synthesized magnetic nanolaminate. We have, independent on method, identified a range of low energy collinear as well as non-collinear magnetic configurations, indicating a highly frustrated magnetic material with several nearly degenerate magnetic states. An experimentally obtained magnetization of only 0.29 per Mn atom in Mn2GaC may be explained by canted spins in an antiferromagnetic configuration of ferromagnetically ordered sub-layers with alternating spin orientation, denoted AFM[0001]$\smal\text{A}\atop\text{4}$. Furthermore, low temperature X-ray diffraction show a new basal plane peak appearing upon a magnetic transition, which is consistent with the here predicted change in inter-layer spacing for the AFM[0001]$\smal\text{A}\atop\text{4}$ configuration.

##### National Category
Physical Sciences
##### Identifiers
urn:nbn:se:liu:diva-104760 (URN)
Available from: 2014-02-25 Created: 2014-02-25 Last updated: 2017-11-03Bibliographically approved
• 5.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Phase stability of Ti2AlC upon oxygen incorporation: A first-principles investigation2010In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 81, no 2, p. 024111-1-024111-8Article in journal (Refereed)

The phase stability of Ti2AlC upon oxygen incorporation has been studied by means of first-principles calculations. Recent experimental observations of this so-called MAX phase (M = early transition metal, A = A-group element, and X = C or N) show that the characteristic nanolaminated structure is retained upon oxygen incorporation, with strong indications of O substituting for C. Therefore, a solid solution of C and O on the carbon sublattice has been simulated by the so-called special quasirandom structure method. Through a developed systematic approach, the enthalpy of formation of Ti2Al(C1−x,Ox) has been compared to all experimentally known competing phases, and has been found favorable for all C to O ratios at the composition of the MAX phase. A negative isostructural formation enthalpy has also been predicted for Ti2Al(C1−x,Ox). Altogether, the results indicate that a large amount of oxygen, at least up to x=0.75, might be present in the Ti2AlC MAX-phase structure without decomposition of the material into its competing phases. Furthermore, an effect of an increased oxygen content is a corresponding increase in the bulk modulus and a change in electronic properties. These results are of importance for further understanding and identification of possible composition range of the MAX-phase oxycarbide, and hence for the prospect of tuning the material properties by a varying incorporation of oxygen.

• 6.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Magnetic nanoscale laminates with tunable exchange coupling from first principles2011In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 84, no 22, p. 220403-Article in journal (Refereed)

The M(n+1)AX(n) (MAX) phases are nanolaminated compounds with a unique combination of metallic and ceramic properties, not yet including magnetism. We carry out a systematic theoretical study of potential magnetic MAX phases and predict the existence of stable magnetic (Cr(1-x)Mn(x))(2)AlC alloys. We show that in this system ferromagnetically ordered Mn layers are exchange coupled via nearly nonmagnetic Cr layers, forming an inherent structure of atomic-thin magnetic multilayers, and that the degree of disorder between Cr and Mn in the alloy can be used to tune the sign and magnitude of the coupling.

• 7.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Complex magnetism in nanolaminated Mn2GaC2014Manuscript (preprint) (Other academic)

We have used first-principles calculations and Heisenberg Monte Carlo simulations to search for the magnetic ground state of Mn2GaC, a recently synthesized magnetic nanolaminate. We have, independent on method, identified a range of low energy collinear as well as non-collinear magnetic configurations, indicating a highly frustrated magnetic material with several nearly degenerate magnetic states. An experimentally obtained magnetization of only 0.29 per Mn atom in Mn2GaC may be explained by canted spins in an antiferromagnetic configuration of ferromagnetically ordered sub-layers with alternating spin orientation, denoted AFM[0001]$\smal\text{A}\atop\text{4}$. Furthermore, low temperature X-ray diffraction show a new basal plane peak appearing upon a magnetic transition, which is consistent with the here predicted change in inter-layer spacing for the AFM[0001]$\smal\text{A}\atop\text{4}$ configuration.

• 8.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
A critical evaluation of GGA plus U modeling for atomic, electronic and magnetic structure of Cr2AlC, Cr2GaC and Cr2GeC2015In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 27, no 9, p. 095601-Article in journal (Refereed)

In this work we critically evaluate methods for treating electron correlation effects in multicomponent carbides using a GGA + U framework, addressing doubts from previous works on the usability of density functional theory in the design of magnetic MAX phases. We have studied the influence of the Hubbard U-parameter, applied to Cr 3d orbitals, on the calculated lattice parameters, magnetic moments, magnetic order, bulk modulus and electronic density of states of Cr2AlC, Cr2GaC and Cr2GeC. By considering non-, ferro-, and five different antiferromagnetic spin configurations, we show the importance of including a broad range of magnetic orders in the search for MAX phases with finite magnetic moments in the ground state. We show that when electron correlation is treated on the level of the generalized gradient approximation (U = 0 eV), the magnetic ground state of Cr(2)AC (A = Al, Ga, Ge) is in-plane antiferromagnetic with finite Cr local moments, and calculated lattice parameters and bulk modulus close to experimentally reported values. By comparing GGA and GGA + U results with experimental data we find that using a U-value larger than 1 eV results in structural parameters deviating strongly from experimentally observed values. Comparisons are also done with hybrid functional calculations (HSE06) resulting in an exchange splitting larger than what is obtained for a U-value of 2 eV. Our results suggest caution and that investigations need to involve several different magnetic orders before lack of magnetism in calculations are blamed on the exchange-correlation approximations in this class of magnetic MAX phases.

• 9.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Correlation between magnetic state and bulk modulus of Cr2AlC2013In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 113, no 21Article in journal (Refereed)

The effect of magnetism on the bulk modulus (B0) of M2AlC (M  = Ti, V, and Cr) has been studied using first principles calculations. We find that it is possible to identify an energetically favorable magnetic Cr2AlC phase without using any adjustable parameter, such as the Hubbard U. Furthermore, we show that an in-plane spin polarized configuration has substantially lower B0 as compared to the non-magnetic model. The existences of local magnetic moments on Cr atoms considerably improve agreement between theory and experiment regarding trends in B0 for M2AlC phases.

• 10.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Magnetic ground state of Cr2AlC, Cr2GaC, and Cr2GeC from first-principles interplay of spin configurations and strong electrons correlation2014Manuscript (preprint) (Other academic)

We have studied the interplay between spin configuration and electron correlations approximations as well as their influence on calculated lattice parameters, magnetic moments, and bulk modulus of the nanolaminated MAX phase materials Cr2AlC, Cr2GaC, and Cr2GeC. By considering non-, ferro- and, and five different antiferromagnetic configurations, we show the importance of including a broad range of magnetic states in search for the ground state. Our calculations show that when electron correlation is treated on the level of the generalized gradient approximation or with an additional Hubbard U interaction term up to a value of 1 eV, the magnetic ground state of Cr2AC (A=Al, Ga, Ge) is in-plane antiferromagnetic with finite Cr local moments and calculated lattice parameters and bulk modulus close to experimentally reported values.

• 11.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Stability trends of MAX phases from first principles2010In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 81, no 22, p. 220102-Article in journal (Refereed)

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.

• 12.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Magnetically driven anisotropic structural changes in the atomic laminate Mn2GaC2016In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 93, no 1, p. 014410-Article in journal (Refereed)

Inherently layered magnetic materials, such as magnetic M(n+1)AX(n) (MAX) phases, offer an intriguing perspective for use in spintronics applications and as ideal model systems for fundamental studies of complex magnetic phenomena. The MAX phase composition M(n+1)AX(n) consists of M(n+1)AX(n) blocks separated by atomically thin A-layers where M is a transition metal, A an A-group element, X refers to carbon and/or nitrogen, and n is typically 1, 2, or 3. Here, we show that the recently discovered magnetic Mn2GaC MAX phase displays structural changes linked to the magnetic anisotropy, and a rich magnetic phase diagram which can be manipulated through temperature and magnetic field. Using first-principles calculations and Monte Carlo simulations, an essentially one-dimensional (1D) interlayer plethora of two-dimensioanl (2D) Mn-C-Mn trilayers with robust intralayer ferromagnetic spin coupling was revealed. The complex transitions between them were observed to induce magnetically driven anisotropic structural changes. The magnetic behavior as well as structural changes dependent on the temperature and applied magnetic field are explained by the large number of low energy, i.e., close to degenerate, collinear and noncollinear spin configurations that become accessible to the system with a change in volume. These results indicate that the magnetic state can be directly controlled by an applied pressure or through the introduction of stress and show promise for the use of Mn2GaC MAX phases in future magnetoelectric and magnetocaloric applications.

• 13.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Uppsala University, Sweden. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Influence of boron vacancies on phase stability, bonding and structure of MB2 (M = Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W) with AlB2 type structure2015In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 27, no 43, p. 435702-Article in journal (Refereed)

Transition metal diborides in hexagonal AlB2 type structure typically form stable MB2 phases for group IV elements (M = Ti, Zr, Hf). For group V (M = V, Nb, Ta) and group VI (M = Cr, Mo, W) the stability is reduced and an alternative hexagonal rhombohedral MB2 structure becomes more stable. In this work we investigate the effect of vacancies on the B-site in hexagonal MB2 and its influence on the phase stability and the structure for TiB2, ZrB2, HfB2, VB2, NbB2, TaB2, CrB2, MoB2, and WB2 using first-principles calculations. Selected phases are also analyzed with respect to electronic and bonding properties. We identify trends showing that MB2 with M from group V and IV are stabilized when introducing B-vacancies, consistent with a decrease in the number of states at the Fermi level and by strengthening of the B-M interaction. The stabilization upon vacancy formation also increases when going from M in period 4 to period 6. For TiB2, ZrB2, and HfB2, introduction of B-vacancies have a destabilizing effect due to occupation of B-B antibonding orbitals close to the Fermi level and an increase in states at the Fermi level.

• 14.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Prediction and synthesis of a family of atomic laminate phases with Kagome-like and in-plane chemical ordering2017In: Science Advances, ISSN 0036-8156, E-ISSN 2375-2548, Vol. 3, no 7, article id e1700642Article in journal (Refereed)

The enigma of MAX phases and their hybrids prevails. We probe transition metal (M) alloying in MAX phases for metal size, electronegativity, and electron configuration, and discover ordering in these MAX hybrids, namely, (V2/3Zr1/3)(2)AlC and (Mo2/3Y1/3)(2)AlC. Predictive theory and verifying materials synthesis, including a judicious choice of alloying M from groups III to VI and periods 4 and 5, indicate a potentially large family of thermodynamically stable phases, with Kagome-like and in-plane chemical ordering, and with incorporation of elements previously not known for MAX phases, including the common Y. We propose the structure to be monoclinic C2/c. As an extension of the work, we suggest a matching set of novel MXenes, from selective etching of the A-element. The demonstrated structural design on simultaneous two-dimensional (2D) and 3D atomic levels expands the property tuning potential of functional materials.

• 15.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Dataset on the structure and thermodynamic and dynamic stability of Mo2ScAlC2 from experiments and first-principles calculations.2017In: Data In Brief, ISSN 2352-3409, Vol. 10, p. 576-582Article in journal (Refereed)

The data presented in this paper are related to the research article entitled "Theoretical stability and materials synthesis of a chemically ordered MAX phase, Mo2ScAlC2, and its two-dimensional derivate Mo2ScC" (Meshkian et al. 2017) [1]. This paper describes theoretical phase stability calculations of the MAX phase alloy MoxSc3-xAlC2 (x=0, 1, 2, 3), including chemical disorder and out-of-plane order of Mo and Sc along with related phonon dispersion and Bader charges, and Rietveld refinement of Mo2ScAlC2. The data is made publicly available to enable critical or extended analyzes.

• 16.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Origin of Chemically Ordered Atomic Laminates (i-MAX): Expanding the Elemental Space by a Theoretical/Experimental Approach2018In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 12, no 8, p. 7761-7770Article in journal (Refereed)

With increased chemical diversity and structural complexity comes the opportunities for innovative materials possessing advantageous properties. Herein, we combine predictive first-principles calculations with experimental synthesis, to explore the origin of formation of the atomically laminated i-MAX phases. By probing (Mo2/3M1/32)(2)AC (where M-2 = Sc, Y and A = Al, Ga, In, Si, Ge, In), we predict seven stable i-MAX phases, five of which should have a retained stability at high temperatures. (Mo2/3Sc1/3)(2)GaC and (Mo2/3Y1/3)(2)GaC were experimentally verified, displaying the characteristic in-plane chemical order of Mo and Sc/Y and Kagome-like ordering of the A-element. We suggest that the formation of i-MAX phases requires a significantly different size of the two metals, and a preferable smaller size of the A-element. Furthermore, the population of antibonding orbitals should be minimized, which for the metals herein (Mo and Sc/Y) means that A elements from Group 13 (Al, Ga, In) are favored over Group 14 (Si, Ge, Sn). Using these guidelines, we foresee a widening of elemental space for the family of i-MAX phases and expect more phases to be synthesized, which will realize useful properties. Furthermore, based on i-MAX phases as parent materials for 2D MXenes, we also expect that the range of MXene compositions will be expanded.

• 17.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Order and disorder in quaternary atomic laminates from first-principles calculations2015In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, no 47, p. 31810-31821Article in journal (Refereed)

We report on the phase stability of chemically ordered and disordered quaternary MAX phases - TiMAlC, TiM2AlC2, MTi2AlC2, and Ti2M2AlC3 where M = Zr, Hf (group IV), M = V, Nb, Ta (group V), and M = Cr, Mo, W (group VI). At 0 K, layered chemically ordered structures are predicted to be stable for M from groups V and VI. By taking into account the configurational entropy, an order-disorder temperature T-disorder can be estimated. TiM2AlC2 (M = Cr, Mo, W) and Ti2M2AlC3 (M = Mo, W) are found with Tdisorder 4 1773 K and are hence predicted to be ordered at the typical bulk synthesis temperature of 1773 K. Other ordered phases, even though metastable at elevated temperatures, may be synthesized by non-equilibrium methods such as thin film growth. Furthermore, phases predicted not to be stable in any form at 0 K can be stabilized at higher temperatures in a disordered form, being the case for group IV, for MTi2AlC2 (M = V, Cr, Mo), and for Ti2M2AlC3 (M = V, Ta). The stability of the layered ordered structures with M from group VI can primarily be explained by Ti breaking the energetically unfavorable stacking of M and C where M is surrounded by C in a face-centered cubic configuration, and by M having a larger electro-negativity than Al resulting in a fewer electrons available for populating antibonding Al-Al orbitals. The results show that these chemically ordered quaternary MAX phases allow for new elemental combinations in MAX phases, which can be used to add new properties to this family of atomic laminates and in turn prospects for tuning these properties.

• 18.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Oxygen incorporation and defect formation in Ti2AlC, V2AlC and Cr2AlC from first-principles calculations2014Manuscript (preprint) (Other academic)

We have studied oxygen incorporation and defect formation in M2AlC (M = Ti, V, Cr) MAX phases using first principles calculations. Evaluating phase stability and electronic structure for different oxygen and/or vacancy configurations, we show that oxygen prefer different lattice sites depending on M-element, which can be correlated to the number of available non-bonding M d-electrons. The results show that oxygen substitutes for carbon in Ti2AlC, while forming an interstitial oxygen in the Al-layer for Cr2AlC. We also predict that oxygen incorporation in Ti2AlC stabilizes the material, which explains the experimentally observed 12.5 at% oxygen (x = 0.5) in Ti2Al(C1-xOx). Due to similar valence electron configuration of Ti2AlC and the hypothetical M2AlC (M =Zr, Hf), we also investigate if oxygen can be used to stabilize the latter MAX phases.

• 19.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Electronic structure, bonding characteristics, and mechanical properties in (W2/3Sc1/3)(2)AIC and (W2/3Y1/3)(2)AIC i-MAX phases from first-principles calculations2018In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 30, no 30, article id 305502Article in journal (Refereed)

With the recent discovery of in-plane chemically ordered MAX phases (i-MAX) of the general formula ((M2/3M1/32)-M-1)(2)AC comes addition of non-traditional MAX phase elements. In the present study, we use density functional theory calculations to investigate the electronic structure, bonding nature, and mechanical properties of the novel (W2/3Sc1/3)(2)AlC and (W2/3Y1/3)(2)AlC i-MAX phases. From analysis of the electronic structure and projected crystal orbital Hamilton populations, we show that the metallic i-MAX phases have significant hybridization between W and C, as well as Sc(Y) and C states, indicative of strong covalent bonding. Substitution of Sc for Y (M-2) leads to reduced bonding strength for W-C and Al-Al interactions while M-2-C and M-2-Al interactions are strengthened. We also compare the Voigt-Reuss-Hill bulk, shear, and Youngs moduli along the series of M-1 = Cr, Mo, and W, and relate these trends to the bonding interactions. Furthermore, we find overall larger moduli for Sc-based i-MAX phases.

• 20.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Electronic structure, bonding characteristics, and mechanical properties in (W2/3Sc1/3)(2)AIC and (W2/3Y1/3)(2)AIC i-MAX phases from first-principles calculations2018In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 30, no 30, article id 305502Article in journal (Refereed)

With the recent discovery of in-plane chemically ordered MAX phases (i-MAX) of the general formula ((M2/3M1/32)-M-1)(2)AC comes addition of non-traditional MAX phase elements. In the present study, we use density functional theory calculations to investigate the electronic structure, bonding nature, and mechanical properties of the novel (W2/3Sc1/3)(2)AlC and (W2/3Y1/3)(2)AlC i-MAX phases. From analysis of the electronic structure and projected crystal orbital Hamilton populations, we show that the metallic i-MAX phases have significant hybridization between W and C, as well as Sc(Y) and C states, indicative of strong covalent bonding. Substitution of Sc for Y (M-2) leads to reduced bonding strength for W-C and Al-Al interactions while M-2-C and M-2-Al interactions are strengthened. We also compare the Voigt-Reuss-Hill bulk, shear, and Youngs moduli along the series of M-1 = Cr, Mo, and W, and relate these trends to the bonding interactions. Furthermore, we find overall larger moduli for Sc-based i-MAX phases.

• 21.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Uppsala University, Sweden . Uppsala University, Sweden . Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Discovery of the Ternary Nanolaminated Compound Nb2GeC by a Systematic Theoretical-Experimental Approach2012In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 109, no 3, p. 035502-Article in journal (Refereed)

Since the advent of theoretical materials science some 60 years ago, there has been a drive to predict and design new materials in silicio. Mathematical optimization procedures to determine phase stability can be generally applicable to complex ternary or higher-order materials systems where the phase diagrams of the binary constituents are sufficiently known. Here, we employ a simplex-optimization procedure to predict new compounds in the ternary Nb-Ge-C system. Our theoretical results show that the hypothetical Nb2GeC is stable, and excludes all reasonably conceivable competing hypothetical phases. We verify the existence of the Nb2GeC phase by thin film synthesis using magnetron sputtering. This hexagonal nanolaminated phase has a and c lattice parameters of similar to 3.24 angstrom and 12.82 angstrom.

• 22.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Characterization of plasma chemistry and ion energy in cathodic arc plasma from Ti-Si cathodes of different compositions2013In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 113, no 16Article in journal (Refereed)

Arc plasma from Ti-Si compound cathodes with up to 25 at. % Si was characterized in a DC arc system with respect to chemistry and charge-state-resolved ion energy. The plasma ion composition showed a lower Si content, diverging up to 12 at. % compared to the cathode composition, yet concurrently deposited films were in accordance with the cathode stoichiometry. Significant contribution to film growth from neutrals is inferred besides ions, since the contribution from macroparticles, estimated by scanning electron microscopy, cannot alone account for the compositional difference between cathode, plasma, and film. The average ion charge states for Ti and Si were higher than reference data for elemental cathodes. This result is likely related to TiSix phases of higher cohesive energies in the compound cathodes and higher effective electron temperature in plasma formation. The ion energy distributions extended up to ∼200 and ∼130 eV for Ti and Si, respectively, with corresponding average energies of ∼60 and ∼30 eV. These averages were, however, not dependent on Si content in the cathode, except for 25 at. % Si where the average energies were increased up to 72 eV for Ti and 47 eV for Si.

• 23.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Synthesis of Ti3AuC2, Ti3Au2C2 and Ti3IrC2 by noble metal substitution reaction in Ti3SiC2 for high-temperature-stable Ohmic contacts to SiC2017In: Nature Materials, ISSN 1476-1122, E-ISSN 1476-4660, Vol. 16, no 8, p. 814-818Article in journal (Refereed)

The large class of layered ceramics encompasses both van der Waals (vdW) and non-vdW solids. While intercalation of noble metals in vdW solids is known, formation of compounds by incorporation of noble-metal layers in non-vdW layered solids is largely unexplored. Here, we show formation of Ti3AuC2 and Ti3Au2C2 phases with up to 31% lattice swelling by a substitutional solid-state reaction of Au into Ti3SiC2 single-crystal thin films with simultaneous out-diffusion of Si. Ti3IrC2 is subsequently produced by a substitution reaction of Ir for Au in Ti3Au2C2. These phases form Ohmic electrical contacts to SiC and remain stable after 1,000 h of ageing at 600 degrees C in air. The present results, by combined analytical electron microscopy and ab initio calculations, open avenues for processing of noble-metal-containing layered ceramics that have not been synthesized from elemental sources, along with tunable properties such as stable electrical contacts for high-temperature power electronics or gas sensors.

• 24.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Ti2Au2C and Ti3Au2C2 formed by solid state reaction of gold with Ti2AlC and Ti3AlC22017In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 53, no 69, p. 9554-9557Article in journal (Refereed)

Incorporation of layers of noble metals in non-van der Waals layered materials may be used to form novel layered compounds. Recently, we demonstrated a high-temperature-induced exchange process of Au with Si in the layered phase Ti3SiC2, resulting in the formation of Ti3AuC2 and Ti3Au2C2. Here, we generalize this technique showing that Au/Ti2AlC and Au/Ti3AlC2 undergo an exchange reaction at 650 [degree]C to form Ti2Au2C and Ti3Au2C2 and determine their structures by electron microscopy, X-ray diffraction, and ab initio calculations. These results imply that noble-metal-containing layered phases should be possible to synthesize in many systems. The metal to be introduced should be inert to the transition-metal carbide layers, and exhibit negative heat of mixing with the initial A element in a liquid phase or two-phase liquid/solid region at the annealing temperature.

• 25.
Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Magnetic MAX phases from theory and experiments: a review2016In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 28, no 43, p. 433003-Article, review/survey (Refereed)

This review presents MAX phases (M is a transition metal, A an A-group element, X is C or N), known for their unique combination of ceramic/metallic properties, as a recently uncovered family of novel magnetic nanolaminates. The first created magnetic MAX phases were predicted through evaluation of phase stability using density functional theory, and subsequently synthesized as heteroepitaxial thin films. All magnetic MAX phases reported to date, in bulk or thin film form, are based on Cr and/or Mn, and they include (Cr,Mn)(2)AlC, (Cr,Mn)(2)GeC, (Cr,Mn)(2)GaC, (Mo,Mn)(2)GaC, (V,Mn)(3)GaC2, Cr2AlC, Cr2GeC and Mn2GaC. A variety of magnetic properties have been found, such as ferromagnetic response well above room temperature and structural changes linked to magnetic anisotropy. In this paper, theoretical as well as experimental work performed on these materials to date is critically reviewed, in terms of methods used, results acquired, and conclusions drawn. Open questions concerning magnetic characteristics are discussed, and an outlook focused on new materials, superstructures, property tailoring and further synthesis and characterization is presented.

• 26.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
A Nanolaminated Magnetic Phase: Mn2GaC2014In: Materials Research Letters, ISSN 2166-3831, Vol. 2, no 2, p. 89-93Article in journal (Refereed)

Layered magnetic materials are fascinating from the point of view of fundamental science as well as applications. Discoveries such as giant magnetoresistance (GMR) in magnetic multilayers have revolutionized data storage and magnetic recording, and concurrently initiated the search for new layered magnetic materials. One group of inherently nanolaminated compounds are the so called Mn+1AXn (MAX) phases. Due to the large number of isostructural compositions, researchers are exploring the wide range of interesting properties, and not primarily functionalization through optimization of structural quality. Magnetic MAX phases have been discussed in the literature, though this is hitherto an unreported phenomenon. However, such materials would be highly interesting, based on the attractive and useful properties attained with layered magnetic materials to date. Here we present a new MAX phase, (Cr1–xMnx)2GeC, synthesized as thin film in heteroepitaxial form, showing single crystal material with unprecedented structural MAX phase quality. The material was identified using first-principles calculations to study stability of hypothetical MAX phases, in an eort to identify a potentially magnetic material. The theory predicts a variety of magnetic behavior depending on the Mn concentration and Cr/Mn atomic conguration within the sublattice. The analyzed thin films display a magnetic signal well above room temperature and with partly ferromagnetic ordering. These very promising results open up a field of new layered magnetic materials, with high potential for electronics and spintronics applications.

• 27.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Magnetic Self-Organized Atomic Laminate from First Principles and Thin Film Synthesis2013In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 110Article in journal (Refereed)

he first experimental realization of a magnetic Mn+1AXn (MAX) phase, (Cr0.75Mn0.25)2GeC, is presented, synthesized as a heteroepitaxial single crystal thin film, exhibiting excellent structural quality. This self-organized atomic laminate is based on the well-known Cr2GeC, with Mn, a new element in MAX phase research, substituting Cr. The compound was predicted using first-principles calculations, from which a variety of magnetic behavior is envisaged, depending on the Mn concentration and Cr/Mn atomic configuration within the sublattice. The analyzed thin films display a magnetic signal at room temperature.

• 28.
Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
Uppsala University, Sweden; Institute Laue Langevin, France. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Long-range antiferromagnetic order in epitaxial Mn2GaC thin films from neutron reflectometry2016In: PHYSICAL REVIEW B, ISSN 2469-9950, Vol. 94, no 2, p. 024416-Article in journal (Refereed)

The nature of the magnetic structure in magnetic so-called MAX phases is a topic of some controversy. Here we present unpolarized neutron-diffraction data between 3.4 and 290.0 K and momentum transfer between Q = 0.0 and 1.1 angstrom(-1), as well as complementary x-ray-diffraction data on epitaxial thin films of the MAX phase material Mn2GaC. This inherently layered material exhibits neutron-diffraction peaks consistent with long-ranged antiferromagnetic order with a periodicity of two structural unit cells. The magnetic structure is present throughout the measured temperature range. The results are in agreement with first-principles calculations of antiferromagnetic structures for this material where the Mn-C-Mn atomic trilayers are found to be ferromagnetically coupled internally but spin flipped or rotated across the Ga layers. The present findings have significant bearing on the discussion regarding the nature of the magnetic structure in magnetic MAX phases.

• 29.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Structural and chemical determination of the new nanolaminated carbide Mo2Ga2C from first principles and materials analysis2015In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 99, p. 157-164Article in journal (Refereed)

Following our recent discovery of a new nanolaminated carbide, Mo2Ga2C, we herein present a detailed structural and chemical analysis of this phase based on ab initio calculations, X-ray photoelectron spectroscopy, high resolution scanning transmission electron microscopy, and neutron powder diffraction. Calculations suggest an energetically and dynamically stable structure for C in the octahedral sites between the Mo layers, with Ga bilayers - stacked in a simple hexagonal arrangement - between the Mo2C layers. The predicted elastic properties are below those of the related nanolaminate Mo2GaC. The predicted structure, including lattice parameters and atomic positions, is experimentally confirmed. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

• 30.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
W-Based Atomic Laminates and Their 2D Derivative W1.33C MXene with Vacancy Ordering2018In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 30, no 21, article id 1706409Article in journal (Refereed)

Structural design on the atomic level can provide novel chemistries of hybrid MAX phases and their MXenes. Herein, density functional theory is used to predict phase stability of quaternary i-MAX phases with in-plane chemical order and a general chemistry (W2/3M1/32)(2)AC, where M-2 = Sc, Y (W), and A = Al, Si, Ga, Ge, In, and Sn. Of over 18 compositions probed, only twowith a monoclinic C2/c structureare predicted to be stable: (W2/3Sc1/3)(2)AlC and (W2/3Y1/3)(2)AlC and indeed found to exist. Selectively etching the Al and Sc/Y atoms from these 3D laminates results in W1.33C-based MXene sheets with ordered metal divacancies. Using electrochemical experiments, this MXene is shown to be a new, promising catalyst for the hydrogen evolution reaction. The addition of yet one more element, W, to the stable of M elements known to form MAX phases, and the synthesis of a pure W-based MXene establishes that the etching of i-MAX phases is a fruitful path for creating new MXene chemistries that has hitherto been not possible, a fact that perforce increases the potential of tuning MXene properties for myriad applications.

• 31.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. University of Iceland, Iceland. Uppsala University, Sweden. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Theoretical stability, thin film synthesis and transport properties of the Mon+1GaCn MAX phase2015In: Physica Status Solidi. Rapid Research Letters, ISSN 1862-6254, E-ISSN 1862-6270, Vol. 9, no 3, p. 197-201Article in journal (Refereed)

The phase stability of Mon +1GaCn has been investigated using ab-initio calculations. The results indicate stability for the Mo2GaC phase only, with a formation enthalpy of 0.4 meV per atom. Subsequent thin film synthesis of Mo2GaC was performed through magnetron sputtering from elemental targets onto Al2O3 [0001], 6H-SiC [0001] and MgO [111] substrates within the temperature range of 500 degrees C and 750 degrees C. High structural quality films were obtained for synthesis on MgO [111] substrates at 590 degrees C. Evaluation of transport properties showed a superconducting behavior with a critical temperature of approximately 7 K, reducing upon the application of an external magnetic field. The results point towards the first superconducting MAX phase in thin film form.

• 32.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Theoretical stability and materials synthesis of a chemically ordered MAX phase, Mo2ScAlC2, and its two-dimensional derivate Mo2ScC2 MXene2017In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 125, p. 476-480Article in journal (Refereed)

We present theoretical prediction and experimental evidence of a new MAX phase alloy, Mo2ScAlC2, with out-of-plane chemical order. Evaluation of phase stability was performed by ab initio calculations based on Density Functional Theory, suggesting that chemical order in the alloy promotes a stable phase, with a formation enthalpy of -24 meV/atom, as opposed to the predicted unstable Mo3AlC2 and Sc3AlC2. Bulk synthesis of Mo2ScAlC2 is achieved by mixing elemental powders of Mo, Sc, Al and graphite which are heated to 1700 degrees C. High resolution transmission electron microscopy reveals a chemically ordered structure consistent with theoretical predictions with one Sc layer sandwiched between two Mo-C layers. The two-dimensional derivative, the MXene, is produced by selective etching of the Al-layers in hydrofluoric acid, resulting in the corresponding chemically ordered Mo2ScC2, i.e. the first Sc-containing MXene. The here presented results expands the attainable range of MXene compositions and widens the prospects for property tuning. (C)2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

• 33.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Materials Chemistry, RWTH-Aachen, D-52074 Aachen, Germany. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Materials Chemistry, RWTH-Aachen, D-52074 Aachen, Germany. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Nanolaminated (Cr,Mn)2AlC alloys by magnetron sputtering and ab initio calculationsManuscript (preprint) (Other academic)

We present an ab initio theoretical analysis of the temperature-dependent stability of hexagonal inherently nanolaminated (Cr1-xMnx)2AlC. The results indicate energetic stability over the composition range x = 0.0 to 0.5 for temperatures 600 to 900 K. Corresponding alloy thin films were grown by magnetron sputtering from four elemental targets. X-ray diffraction in combination with analytical transmission electron microscopy including electron energy-loss spectroscopy and energy dispersive X-ray spectroscopy analysis revealed that the films were epitaxial (0001)-oriented single crystals with x up to 0.16.

• 34.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Rhein Westfal TH Aachen, Germany . Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Rhein Westfal TH Aachen, Germany . Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Synthesis and ab initio calculations of nanolaminated (Cr,Mn)2AlC compounds2013In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 87, no 9Article in journal (Refereed)

We present an ab initio theoretical analysis of the temperature-dependent stability of inherently nanolaminated (Cr1−xMnx)2AlC. The results indicate energetic stability over the composition range x = 0.0 to 0.5 for temperatures ≥600 K. Corresponding thin film compounds were grown by magnetron sputtering from four elemental targets. X-ray diffraction in combination with analytical transmission electron microscopy, including electron energy-loss spectroscopy and energy dispersive x-ray spectroscopy analysis, revealed that the films were epitaxial (0001)-oriented single-crystals with x up to 0.16.

• 35.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Oxygen incorporation in Ti2AlC thin films studied by electron energy loss spectroscopy and ab initio calculations2013In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 48, no 10, p. 3686-3691Article in journal (Refereed)

Substitution of C with O in hexagonal inherently nanolaminated Ti2AlC has been studied experimentally and theoretically. Ti2Al(C1−x O x ) thin films with x ≤ 0.52 are synthesized by both cathodic arc deposition with the uptake of residual gas O, and solid-state reaction between understoichiometric TiC y and Al2O3(0001) substrates. The compositional analysis is made by analytical transmission electron microscopy, including electron energy loss spectroscopy. Furthermore, predictive ab initio calculations are performed to evaluate the influence of substitutional O on the shear stress at different strains for slip on the (0001) basal plane in the [−1010] and [1−210] directions.

• 36.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Phase stability of Crn+1GaCn MAX phases from first principles and Cr2GaC thin-film synthesis using magnetron sputtering from elemental targets2013In: Physica Status Solidi. Rapid Research Letters, ISSN 1862-6254, E-ISSN 1862-6270, Vol. 7, no 11, p. 971-974Article in journal (Refereed)

Ab-initio calculations have been used to investigate the phase stability and magnetic state of Crn+ 1GaCn MAX phase. Cr2GaC (n = 1) was predicted to be stable, with a ground state corresponding to an antiferromagnetic spin configuration. Thin-film synthesis by magnetron sputtering from elemental targets, including liquid Ga, shows the formation of Cr2GaC, previously only attained from bulk synthesis methods. The films were deposited at 650 degrees C on MgO(111) substrates. X-ray diffraction and high-resolution transmission electron microscopy show epitaxial growth of (000) MAX phase.

• 37.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology. University of Sydney. University of Sydney.
Oxygen incorporation in Ti2AlC: Tuning of anisotropic conductivity2010In: APPLIED PHYSICS LETTERS, ISSN 0003-6951, Vol. 97, no 7, p. 073103-Article in journal (Refereed)

The substitution of oxygen for carbon in Ti2AlC M((n+1))AX(n) (MAX) phase, forming Ti2AlC1-xOx, has recently been reported. In this paper we simulate the effect of oxygen incorporation on mechanical and electronic properties using ab initio calculations. While the mechanical properties are not sensitive to the change in composition, the electronic properties can be tuned by varying the oxygen concentration. As the concentration increases, the conduction changes from in plane, typical of MAX phases, to conduction also in the c-direction. The conduction along c passes from insulating to n-type and then finally to p-type. These findings reveal an anisotropic semiconducting material.

• 38.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Two-dimensional Mo1.33C MXene with divacancy ordering prepared from parent 3D laminate with in-plane chemical ordering2017In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 8, article id 14949Article in journal (Refereed)

The exploration of two-dimensional solids is an active area of materials discovery. Research in this area has given us structures spanning graphene to dichalcogenides, and more recently 2D transition metal carbides (MXenes). One of the challenges now is to master ordering within the atomic sheets. Herein, we present a top-down, high-yield, facile route for the controlled introduction of ordered divacancies in MXenes. By designing a parent 3D atomic laminate, (Mo2/3Sc1/3)(2)AlC, with in-plane chemical ordering, and by selectively etching the Al and Sc atoms, we show evidence for 2D Mo1.33C sheets with ordered metal divacancies and high electrical conductivities. At similar to 1,100 F cm(-3), this 2D material exhibits a 65% higher volumetric capacitance than its counterpart, Mo2C, with no vacancies, and one of the highest volumetric capacitance values ever reported, to the best of our knowledge. This structural design on the atomic scale may alter and expand the concept of property-tailoring of 2D materials.

• 39.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Atomically Layered and Ordered Rare-Earth i-MAX Phases: A New Class of Magnetic Quaternary Compounds2019In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 31, no 7, p. 2476-2485Article in journal (Refereed)

In 2017, we discovered quaternary i-MAX phases atomically layered solids, where M is an early transition metal, A is an A group element, and X is C-with a ((M2/3M1/32)-M-1)(2)AC chemistry, where the M-1 and M-2 atoms are in-plane ordered. Herein, we report the discovery of a class of magnetic i-MAX phases in which bilayers of a quasi-2D magnetic frustrated triangular lattice overlay a Mo honeycomb arrangement and an Al Kagome lattice. The chemistry of this family is (Mo2/3RE1/3)(2)AlC, and the rare-earth, RE, elements are Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, and Lu. The magnetic properties were characterized and found to display a plethora of ground states, resulting from an interplay of competing magnetic interactions in the presence of magnetocrystalline anisotropy.

• 40.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
First-principles calculations of the electronic, vibrational, and elastic properties of the magnetic laminate Mn2GaC2014In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 116, no 10, p. 103511-Article in journal (Refereed)

In this paper, we report the by first-principles predicted properties of the recently discovered magnetic MAX phase Mn2GaC. The electronic band structure and vibrational dispersion relation, as well as the electronic and vibrational density of states, have been calculated. The band structure close to the Fermi level indicates anisotropy with respect to electrical conductivity, while the distribution of the electronic and vibrational states for both Mn and Ga depend on the chosen relative orientation of the Mn spins across the Ga sheets in the Mn–Ga–Mn trilayers. In addition, the elastic properties have been calculated, and from the five elastic constants, the Voigt bulk modulus is determined to be 157 GPa, the Voigt shear modulus 93 GPa, and the Young's modulus 233 GPa. Furthermore, Mn2GaC is found relatively elastically isotropic, with a compression anisotropy factor of 0.97, and shear anisotropy factors of 0.9 and 1, respectively. The Poisson's ratio is 0.25. Evaluated elastic properties are compared to theoretical and experimental results for M 2 AC phases where M = Ti, V, Cr, Zr, Nb, Ta, and A = Al, S, Ge, In, Sn

• 41.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Magnetic exchange interactions and critical temperature of the nanolaminate Mn2GaC from first-principles supercell methods2016In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 93, no 5Article in journal (Refereed)

In this work, we employ and critically evaluate a first-principles approach based on supercell calculations for predicting the magnetic critical order-disorder temperature 𝑇𝑐 . As a model material we use the recently discovered nanolaminate Mn2GaC.

First, we derive the exchange interaction parameters 𝐽𝑖𝑗 between pairs of Mn atoms on sites 𝑖 and 𝑗 of the bilinear Heisenberg Hamiltonian using the novel magnetic direct cluster averaging method (MDCA), and then compare the 𝐽’s from the MDCA calculations to the same parameters calculated using the Connolly-Williams method. We show that the two methods yield closely matching results, but observe that the MDCA method is computationally less effective when applied to highly ordered phases such as Mn2GaC.

Secondly, Monte Carlo simulations are used to derive the magnetic energy, specific heat, and 𝑇𝑐 . For Mn2GaC, we find 𝑇𝑐 = 660 K. The uncertainty in the calculated 𝑇𝑐 caused by possible uncertainties in the 𝐽’s is discussed and exemplified in our case by an analysis of the impact of the statistical uncertainties of the MDCA-derived 𝐽’s, resulting in a 𝑇𝑐 distribution with a standard deviation of 133 K.

• 42.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Max Planck Institute Eisenforsch GmbH, Germany. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Phase stability of the nanolaminates V2Ga2C and (Mo1-xVx)(2)Ga2C from first-principles calculations2016In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 18, no 18, p. 12682-12688Article in journal (Refereed)

We here use first-principles calculations to investigate the phase stability of the hypothetical laminated material V2Ga2C and the related alloy (Mo1-xVx)(2)Ga2C, the latter for a potential parent material for synthesis of (Mo1-xVx)(2)C, a new two-dimensional material in the family of so called MXenes. We predict that V2Ga2C is thermodynamically stable with respect to all identified competing phases in the ternary V-Ga-C phase diagram. We further calculate the stability of ordered and disordered configurations of Mo and V in (Mo1-xVx)(2)Ga2C and predict that ordered (Mo1-xVx)(2)Ga2C for x &lt;= 0.25 is stable, with an order-disorder transition temperature of similar to 1000 K. Furthermore, (Mo1-xVx)(2)Ga2C for x = 0.5 and x &gt;= 0.75 is suggested to be stable, but only for disordered Mo-V configurations, and only at elevated temperatures. We have also investigated the electronic and elastic properties of V2Ga2C; the calculated bulk, shear, and Youngs modulus are 141, 94, and 230 GPa, respectively.

• 43.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Phase stability of the nanonlaminates V2Ga2C and (Mo1-xVx)2Ga2C from first-principles calculations2016Manuscript (preprint) (Other academic)

We here use first-principles calculations to investigate the phase stability of the hypothetical laminated materials V2Ga2C and the related alloy (Mo1-xVx)2Ga2C, the latter for a potential parent material for synthesis of (Mo1-xVx)2C, a new two-dimensional material in the family of so called MXenes. We predict that V2Ga2C is thermodynamically stable with respect to all identified competing phases in the ternary VGa-C phase diagram. We further predict the stability for ordered and disordered configurations of Mo and V in (Mo1-xVx)2Ga2C and predict that ordered (Mo1-xVx)2Ga2C for 𝑥 ≤ 0.25 is stable, with an orderdisorder transition temperature of ~1000 K. Furthermore, (Mo1-xVx)2Ga2C for 𝑥 = 0.5 and 𝑥 ≥ 0.75 is suggested to potentially be stable, but only for disordered Mo-V configurations, and only at elevated temperatures. We have also investigated the electronic and elastic properties of V2Ga2C; the calculated bulk, shear, and Young’s modulus are 141, 95, and 232 GPa, respectively.

• 44.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Temperature dependent phase stability of nanolaminated ternaries from first-principles calculations2014In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 91, p. 251-257Article in journal (Refereed)

Methods based on first-principles calculations have proven effective for predicting the thermodynamic stability of materials that have not previously been considered. However, the vast majority of these predictions are based on 0 K calculations, which means that little is known about the effects of temperature on their accuracy. This causes considerable uncertainty with respect to stability predictions of new hypothetical phases. In this work we combine first-principles calculations with an optimization procedure to calculate the phase stability as a function of temperature for Ti2AlC, Ti3AlC2 and Ti4AlC3 MAX phases with respect to their most competing phases in the Ti-Al-C phase diagram, in a temperature interval from 0 to 2000 K. To model nonzero temperatures, we include effects from the electronic and vibrational free energies to the Gibbs free energy for all relevant competing phases. We show that, due to a mutual cancellation of the temperature dependent energy terms, the results of neither the harmonic nor the quasiharmonic calculations differ significantly from the calculated 0 K formation energies. We thus provide a plausible explanation for the success of previous 0 K predictions, an explanation which also serves as evidence for the hypothesis that the phase stability in many materials systems is primarily governed by the 0 K energy terms.

• 45.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Effect of Ti-Al cathode composition on plasma generation and plasma transport in direct current vacuum arc2014In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 115, no 12, p. 123301-Article in journal (Refereed)

DC arc plasma from Ti, Al, and Ti1-xAlx (x = 0.16, 0.25, 0.50, and 0.70) compound cathodes was characterized with respect to plasma chemistry and charge-state-resolved ion energy. Scanning electron microscopy, X-ray diffraction, and Energy-dispersive X-ray spectroscopy of the deposited films and the cathode surfaces were used for exploring the correlation between cathode-, plasma-, and film composition. Experimental work was performed at a base pressure of 10(-6) Torr, to exclude plasma-gas interaction. The plasma ion composition showed a reduction of Al of approximately 5 at. % compared to the cathode composition, while deposited films were in accordance with the cathode stoichiometry. This may be explained by presence of neutrals in the plasma/vapour phase. The average ion charge states (Ti = 2.2, Al = 1.65) were consistent with reference data for elemental cathodes, and approximately independent on the cathode composition. On the contrary, the width of the ion energy distributions (IEDs) were drastically reduced when comparing the elemental Ti and Al cathodes with Ti0.5Al0.5, going from similar to 150 and similar to 175 eV to similar to 100 and similar to 75 eV for Ti and Al ions, respectively. This may be explained by a reduction in electron temperature, commonly associated with the high energy tail of the IED. The average Ti and Al ion energies ranged between similar to 50 and similar to 61 eV, and similar to 30 and similar to 50 eV, respectively, for different cathode compositions. The attained energy trends were explained by the velocity rule for compound cathodes, which states that the most likely velocities of ions of different mass are equal. Hence, compared to elemental cathodes, the faster Al ions will be decelerated, and the slower Ti ions will be accelerated when originating from compound cathodes. The intensity of the macroparticle generation and thickness of the deposited films were also found to be dependent on the cathode composition. The presented results may be of importance for choice of cathodes for thin film depositions involving compound cathodes.

1 - 45 of 45
Cite
Citation style
• apa
• harvard1
• ieee
• modern-language-association-8th-edition
• vancouver
• oxford
• Other style
More styles
Language
• de-DE
• en-GB
• en-US
• fi-FI
• nn-NO
• nn-NB
• sv-SE
• Other locale
More languages
Output format
• html
• text
• asciidoc
• rtf