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Structural and chemical determination of the new nanolaminated carbide Mo2Ga2C from first principles and materials analysis
Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.ORCID-id: 0000-0001-5036-2833
Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
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2015 (Engelska)Ingår i: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 99, s. 157-164Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

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.

Ort, förlag, år, upplaga, sidor
PERGAMON-ELSEVIER SCIENCE LTD , 2015. Vol. 99, s. 157-164
Nyckelord [en]
First principles; Phase stability; Nanolaminated material; Crystal structure; Mo2Ga2C
Nationell ämneskategori
Fysik
Identifikatorer
URN: urn:nbn:se:liu:diva-122193DOI: 10.1016/j.actamat.2015.07.063ISI: 000362145400017OAI: oai:DiVA.org:liu-122193DiVA, id: diva2:865059
Anmärkning

Funding Agencies|Swedish Research Council [621-2011-4420, 642-2013-8020, 621-2014-4890]; Swedish Foundation for Strategic Research through the Synergy Grant FUNCASE Functional Carbides for Advanced Surface Engineering; Future Research Leaders 5 Program; ERC [258509]; Knut and Alice Wallenberg Foundation

Tillgänglig från: 2015-10-26 Skapad: 2015-10-23 Senast uppdaterad: 2018-05-24
Ingår i avhandling
1. Thin Film Synthesis of New Nanolaminated Ternary Carbides
Öppna denna publikation i ny flik eller fönster >>Thin Film Synthesis of New Nanolaminated Ternary Carbides
2016 (Engelska)Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

Ternary transition metal carbides with inherently nanolaminated crystal structure are a class of materials with typically higher damage tolerance, better machinability and lower brittleness compared to the binary counterparts, yet retaining their satisfactory electrical and thermal conductivity. Their interesting properties can be related to the laminated structure. Though studies of their properties based on calculations and bulk materials have suggested potential thin film applications, such as high temperature hard coatings and electrical contacts, a relatively small number of these phases have been synthesized as thin films.  Investigation of thin film deposition of these inherently nanolaminated materials further the understanding of their phase formation and crystal growth.

Motivated by predicted superconductivity and thermoelectric properties of molybdenum carbides and related layered molybdenum compounds, nanolaminated materials in the Mo-Ga-C ternary system were studied. Apart from the previously reported Mo2GaC, a new layered carbide, Mo2Ga2C, was synthesized in both thin film and bulk form with a postulated crystal structure related to Mo2GaC. The proposed structure was further validated by first principles calculations, showing higher stability compared to other crystal structure as well as other competing phases. The calculated lattice parameters were consistent with values from Rietveld analysis of X-ray and neutron diffraction patterns. In addition, both scanning transmission electron microscopy and X-ray photoelectron spectroscopy showed experimental evidence of the close structural-chemical relation between Mo2Ga2C and Mo2GaC.

Driven by a need of high temperature protective coatings in nuclear applications, Zr-based nanolaminated carbides have become more attractive. In this work, another nanolaminated carbide, Zr2Al3C4, was synthesized in thin film form by pulsed cathodic arc deposition. Formation of the Zr2Al3C4 phase and its competing phases was studied with X-ray diffraction of thin films deposited with varying incoming flux compositions, temperatures and substrate materials. On 4H-SiC(001) substrates, highly phase-pure epitaxial Zr2Al3C4 films were formed, whereas depositions on Al2O3(001) substrates resulted in competing phases. A growth behavior similar to that of nanolaminated Mn+1AXn phases (M is a group 3-7 transition metal; A is commonly a group 13-14 element; X is C or N; n = 1 - 3) was observed, despite the structuraland chemical differences between Zr2Al3C4 and MAX phases.

Ort, förlag, år, upplaga, sidor
Linköping: Linköping University Electronic Press, 2016. s. 41
Serie
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1728
Nationell ämneskategori
Fysik
Identifikatorer
urn:nbn:se:liu:diva-125289 (URN)10.3384/lic.diva-125289 (DOI)978-91-7685-960-5 (ISBN)
Presentation
2015-10-02, Jordan/Fermi, J402, Fysikhuset, Campus Valla, Linköping, 10:15 (Engelska)
Opponent
Handledare
Anmärkning

The series name Linköping Studies in Science and Technology Licentiate Thesis is incorrect. Correct series name is Linköping Studies in Science and Technology. Thesis.

Tillgänglig från: 2016-02-19 Skapad: 2016-02-19 Senast uppdaterad: 2019-10-29Bibliografiskt granskad
2. Phase Formation of Nanolaminated Transition Metal Carbide Thin Films
Öppna denna publikation i ny flik eller fönster >>Phase Formation of Nanolaminated Transition Metal Carbide Thin Films
2017 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

Research on inherently nanolaminated transition metal carbides is inspired by their unique properties combining metals and ceramics, such as higher damage tolerance, better machinability and lower brittleness compared to the binary counterparts, yet retaining the metallic conductivity. The interesting properties are related to their laminated structure, composed of transition-metalcarbide layers interleaved by non-transition-metal (carbide) layers. These materials in thin-film form are particularly interesting for potential applications such as protective coatings and electrical contacts. The goal of this work is to explore nanolaminated transition metal carbides from the aspects of phase formation and crystal growth during thin-film synthesis. This was realized by studying phases in select material systems synthesized from two major approaches, namely, fromdirect-deposition and post-deposition treatment.

The first approach was used in studies on the Mo-Ga-C and Zr-Al-C systems. In the former system, intriguing properties have been predicted for the 3D phases and their 2D derivatives (socalled MXenes), while in the latter system, the phases are interesting for nuclear applications. In this work, the discovery of a new Mo-based nanolaminated ternary carbide, Mo2Ga2C, is evidenced from thin-film and bulk processes. Its structure was determined using theoretical and experimental techniques, showing that Mo2Ga2C has Ga double-layers in simple hexagonal stacking between adjacent Mo2C layers, and therefore is structurally very similar to Mo2GaC, except for the additional Ga layers. For the Zr-Al-C system, the optimization of phase composition and structure of Zr2Al3C4 in a thin-film deposition process was studied by evaluating the effect of deposition parameters. I concluded that the formation of Zr2Al3C4 is favored with a plasma flux overstoichiometric in Al, and with a minimum lattice-mismatch to the substrates. Consequently, epitaxial Zr2Al3C4 thin film of high quality were deposited on 4H-SiC(001) substrates at 800 °C.

With the approach of post-deposition treatment, the studies were focused on a new method of thermally-induced selective substitution reaction of Au for the non-transition-metal layers in nanolaminated carbides. Here, the reaction mechanism has been explored in Al-containing (Ti2AlC

and Ti3AlC2) and Ga-containing (Mo2GaC and Mo2Ga2C) phases. The Al and Ga in these phases were selectively replaced by Au while the carbide layers remained intact, resulting in the formation of new layered phases, Ti2Au2C, Ti3Au2C2, Mo2AuC, and Mo2(Au1-xGax)2C, respectively. The substitution reaction was explained by fast outward diffusion of the Al or Ga being attracted to the surface Au, in combination with back-filling of Au, which is chemically inert to the carbide layers,to the vacancies.

The substitution reaction was further applied to Ga-containing nanolaminated carbides, (Cr0.5Mn0.5)2GaC and Mo2GaC, motivated by development of novel magnetic nanolaminates. The former experiment resulted in the formation of (Cr0.5Mn0.5)2AuC, where the retained (Cr0.5Mn0.5)2C layers allowed a comparative study on the magnetic properties under the exchange of Ga for Au. After Au substitution, reduction in the Curie temperature and the saturation magnetization were observed, showing a weakened magnetic exchange interaction of the magnetic (Cr0.5Mn0.5)Clayers across the Au. In the Mo2GaC case, an Fe-containing MAX phase, Mo2AC with 50 at.% of Fe on the A site, was synthesized through selective substitution of Au-Fe alloy for the Ga layers, showing the first direct evidence for Fe in the MAX-phase structure. The substitution of Fe did not take place on another Mo2GaC sample tested for Fe exchange only, indicating the essential role of Au in catalyzing the Fe-substitution reaction.

The knowledge gained from this thesis work contributes to improved approaches for attaining thin films of nanolaminated transition metal carbides with desired phase composition and crystal quality. The reports on the new nanolaminated phases through exchange interactions are likely to expand the family of nanolaminated carbides and advance their properties, and trigger more studies on related (quasi-) 2D materials.

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Linköping: Linköping University Electronic Press, 2017. s. 3
Serie
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1850
Nationell ämneskategori
Oorganisk kemi Materialkemi Den kondenserade materiens fysik Fysikalisk kemi
Identifikatorer
urn:nbn:se:liu:diva-137367 (URN)10.3384/diss.diva-137367 (DOI)978-91-7685-526-3 (ISBN)
Disputation
2017-06-07, Planck, Fysikhuset, Campus Valla, Linköping, 10:15 (Engelska)
Opponent
Handledare
Tillgänglig från: 2017-05-15 Skapad: 2017-05-15 Senast uppdaterad: 2019-10-11Bibliografiskt granskad
3. Synthesis and characterization of Mo- and W-based atomic laminates
Öppna denna publikation i ny flik eller fönster >>Synthesis and characterization of Mo- and W-based atomic laminates
2018 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

Mn+1AXn (MAX) phases are inherently nanolaminated compounds based on transition metals (M), A group elements (A), and carbon or/and nitrogen (X), which exhibit a unique combination of ceramic and metallic properties. My thesis work has focused on exploring novel MAX phase chemistries, including elemental combinations beyond those traditionally used for MAX phases, and their graphene-analogous 2D counterpart, MXenes.  

The first part of the thesis investigates Mo-based MAX phases, which are among the least studied, despite indication of superconducting properties and potential for derivation of Mo-based MXenes. Initially, I performed theoretical calculations focused on evaluation of phase stability of the Mon+1GaCn MAX phases, and synthesized the predicted stable Mo2GaC in thin film form using DC magnetron sputtering. Close to phase pure epitaxial films were grown at ~590 °C, and electrical resistivity measurements using a four-point probe technique suggest a superconducting behavior with a critical temperature of ~7 K. The follow-up of this work, was synthesis of a new MAX related material, Mo2Ga2C, also by means of DC magnetron sputtering. The theoretical predictions as well as the materials characterization by X-ray diffraction and neutron powder diffraction, suggested a Ga bilayer interleaved between a set of Mo2C blocks, arranged in a simple hexagonal structure.   

It is known that selectively etching of the A-layer in a MAX phase, shown for A=Al, can lead to realization of a MXene. Hence, the next step in my research was to explore the possibility of etching of A=Ga in Mo2GaC as well as in Mo2Ga2C, targeting a Mo2C MXene, as motivated by theoretically proposed superior thermoelectric properties of this 2D material. While Mo2GaC did not allow removal of the A-layer, I showed that Mo2C MXene could be realized from etching Mo2Ga2C thin films, removing the Ga bilayer, in 50% hydrofluoric acid at a temperature of ~50 °C for a duration of ~3 h. Hence, the results did not only produce the first Mo-based MXene, it also showed that MXenes can be obtained for etching A-elements other than Al. This, in turn, increase the pathways for expanding the family of MXenes.    

I thereafter set out to explore the magnetic properties resulting from Mn-alloying of the non-magnetic Mo2GaC MAX phase. For that purpose, (Mo,Mn)2GaC was synthesized using a  DC magnetron sputtering system with Ga and C as elemental targets and a 1:1 atomic ratio  Mo:Mn compound target. Heteroepitaxial films on MgO(111) substrates were grown at  ~530 °C, as confirmed by X-ray diffraction. Compositional analysis using energy dispersive X-ray spectroscopy showed a 2:1 ratio of the M- and A-elements and a 1:1 ratio for the Mo and Mn atoms in the film. Vibrating sample magnetometry was utilized to measure the magnetic behavior of the films, showing a magnetic response up to at least 300 K, and with a coercive field of 0.06 T, which is the highest reported for any MAX phase to date.  

The second part of my research has been dedicated to realizing new MAX phase related, chemically ordered compounds and their MXene derivatives, and to initiate exploration of their properties. Materials synthesis was performed by pressureless bulk sintering, and inspired by theoretical calculations we showed evidence for a new so called o-MAX phase, Mo2ScAlC2, with an out-of-plane chemically ordered structure. It is the first experimentally verified Sc-containing MAX phase, which makes its corresponding MXene, Mo2ScC2, also presented in this work, the first MXene including Sc. Moreover, I discovered two so called i-MAX phases including W, (W2/3Sc1/3)2AlC and (W2/3Y1/3)2AlC, which display in-plane chemical ordering in the M-layer. Furthermore, both was shown to allow synthesis of their corresponding 2D counterpart; W1.33C MXene, with ordered vacancies.  Initial test on these novel MXenes showed a high potential for hydrogen evolution reaction.  

Altogether, I have in my thesis work realized 6 novel MAX phases and related materials, and have shown evidence for 4 new MXenes. These materials inspire a wide range of future studies, with respect to fundamental properties as well as potential for future applications.   

Ort, förlag, år, upplaga, sidor
Linköping: Linköping University Electronic Press, 2018. s. 59
Serie
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1933
Nationell ämneskategori
Den kondenserade materiens fysik Nanoteknik
Identifikatorer
urn:nbn:se:liu:diva-148012 (URN)10.3384/diss.diva-148012 (DOI)9789176853122 (ISBN)
Disputation
2018-06-11, Planck, Fysikhuset, Campus Valla, Linköping, 10:15 (Engelska)
Opponent
Handledare
Tillgänglig från: 2018-05-24 Skapad: 2018-05-24 Senast uppdaterad: 2019-09-30Bibliografiskt granskad

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