Publications by authors named "Martin Dahlqvist"

19 Publications

  • Page 1 of 1

Boridene: Two-dimensional MoB with ordered metal vacancies obtained by chemical exfoliation.

Science 2021 08;373(6556):801-805

Materials Design, Department of Physics, Chemistry and Biology (IFM), Linköping University, SE-581 83 Linköping, Sweden.

Extensive research has been invested in two-dimensional (2D) materials, typically synthesized by exfoliation of van der Waals solids. One exception is MXenes, derived from the etching of constituent layers in transition metal carbides and nitrides. We report the experimental realization of boridene in the form of single-layer 2D molybdenum boride sheets with ordered metal vacancies, MoBT (where T is fluorine, oxygen, or hydroxide surface terminations), produced by selective etching of aluminum and yttrium or scandium atoms from 3D in-plane chemically ordered (MoY)AlB and (MoSc)AlB in aqueous hydrofluoric acid. The discovery of a 2D transition metal boride suggests a wealth of future 2D materials that can be obtained through the chemical exfoliation of laminated compounds.
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http://dx.doi.org/10.1126/science.abf6239DOI Listing
August 2021

Out-Of-Plane Ordered Laminate Borides and Their 2D Ti-Based Derivative from Chemical Exfoliation.

Adv Mater 2021 Sep 5;33(38):e2008361. Epub 2021 Aug 5.

Thin Film Physics Division, Department of Physics, Chemistry and Biology (IFM), Linköping University, Linköping, SE-581 83, Sweden.

Exploratory theoretical predictions in uncharted structural and compositional space are integral to materials discoveries. Inspired by M SiB (T2) phases, the finding of a family of laminated quaternary metal borides, M' M″SiB , with out-of-plane chemical order is reported here. 11 chemically ordered phases as well as 40 solid solutions, introducing four elements previously not observed in these borides are predicted. The predictions are experimentally verified for Ti MoSiB , establishing Ti as part of the T2 boride compositional space. Chemical exfoliation of Ti MoSiB and select removal of Si and MoB sub-layers is validated by derivation of a 2D material, TiO Cl , of high yield and in the form of delaminated sheets. These sheets have an experimentally determined direct band gap of ≈4.1 eV, and display characteristics suitable for supercapacitor applications. The results take the concept of chemical exfoliation beyond currently available 2D materials, and expands the envelope of 3D and 2D candidates, and their applications.
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http://dx.doi.org/10.1002/adma.202008361DOI Listing
September 2021

In-plane ordered quaternaryM4/3'M2/3″AlB2phases (-MAB): electronic structure and mechanical properties from first-principles calculations.

J Phys Condens Matter 2021 May 21;33(25). Epub 2021 May 21.

Thin Films Physics, Department of Physics, Chemistry, and Biology, Linköping University, SE-581-83 Linköping, Sweden.

We have by means of first principles density functional theory calculations studied the mechanical and electronic properties of the so called-MAB phases,'″AlB, where' = Cr, Mo, W and″ = Sc, Y. These phases, experimentally verified for MoScAlBand MoYAlB, display an atomically laminated structure with in-plane chemical order between the' and″ elements. Structural properties, along with elastic constants and moduli, are predicted for different structural symmetries, including the reportedR3̄m(#166) space group. We find all considered-MAB phases to be metallic with a significant peak in the electronic structure at the Fermi level and no significant anisotropy in the electronic band structure. The simulations also indicate that they are rather hard and stiff, in particular the Cr-based ones, with a Young's modulusof 325 GPa for″ = Sc. The Mo-based phases are similar, with= 299 GPa for″ = Sc, which is higher than the corresponding laminated carbides (-MAX phases).
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http://dx.doi.org/10.1088/1361-648X/abf9bcDOI Listing
May 2021

Theoretical Prediction and Synthesis of a Family of Atomic Laminate Metal Borides with In-Plane Chemical Ordering.

J Am Chem Soc 2020 Oct 13;142(43):18583-18591. Epub 2020 Oct 13.

Thin Film Physics, Department of Physics, Chemistry and Biology (IFM), Linköping University, SE-581 83 Linköping, Sweden.

All atomically laminated MAB phases (M = transition metal, A = A-group element, and B = boron) exhibit orthorhombic or tetragonal symmetry, with the only exception being hexagonal TiInB. Inspired by the recent discovery of chemically ordered hexagonal carbides, i-MAX phases, we perform an extensive first-principles study to explore chemical ordering upon metal alloying of MAlB (M from groups 3 to 9) in orthorhombic and hexagonal symmetry. Fifteen stable novel phases with in-plane chemical ordering are identified, coined i-MAB, along with 16 disordered stable alloys. The predictions are verified through the powder synthesis of MoYAlB and MoScAlB of space group 3̅ (no. 166), displaying the characteristic in-plane chemical order of Mo and Y/Sc and Kagomé ordering of the Al atoms, as evident from X-ray diffraction and electron microscopy. The discovery of i-MAB phases expands the elemental space of these borides with M = Sc, Y, Zr, Hf, and Nb, realizing an increased property tuning potential of these phases as well as their suggested potential two-dimensional derivatives.
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http://dx.doi.org/10.1021/jacs.0c08113DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7596753PMC
October 2020

Impact of strain, pressure, and electron correlation on magnetism and crystal structure of MnGaC from first-principles.

Sci Rep 2020 Jul 9;10(1):11384. Epub 2020 Jul 9.

Thin Film Physics, Department of Physics, Chemistry and Biology (IFM), Linköping University, 581 83, Linköping, Sweden.

The atomically laminated MnGaC has previously been synthesized as a heteroepitaxial thin film and found to be magnetic with structural changes linked to the magnetic anisotropy. Related theoretical studies only considered bulk conditions and thus neglected the influence from possible strain linked to the choice of substrate. Here we employ first principles calculations considering different exchange-correlation functionals (PBE, PW91, PBEsol, AM05, LDA) and effect from use of + U methods (or not) combined with a magnetic ground-state search using Heisenberg Monte Carlo simulations, to study influence from biaxial in-plane strain and external pressure on the magnetic and crystal structure of MnGaC. We find that PBE and PBE + U, with U ≤ 0.25 eV, gives both structural and magnetic properties in quantitative agreement with available experimental data. Our results also indicate that strain related to choice of substrate or applied pressure is a route for accessing different spin configurations, including a ferromagnetic state. Moreover, the easy axis is parallel to the atomic planes and the magnetocrystalline anisotropy energy can be increased through strain engineering by expanding the in-plane lattice parameter a. Altogether, we show that a quantitative description of the structural and magnetic properties of MnGaC is possible using PBE, which opens the way for further computational studies of these and related materials.
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http://dx.doi.org/10.1038/s41598-020-68377-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7347948PMC
July 2020

Predictive theoretical screening of phase stability for chemical order and disorder in quaternary 312 and 413 MAX phases.

Nanoscale 2020 Jan;12(2):785-794

Thin Film Physics, Department of Physics, Chemistry and Biology (IFM), Linköping University, SE-581 83 Linköping, Sweden.

In this work we systematically explore a class of atomically laminated materials, Mn+1AXn (MAX) phases upon alloying between two transition metals, M' and M'', from groups III to VI (Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W). The materials investigated focus on so called o-MAX phases with out-of-plane chemical ordering of M' and M'', and their disordered counterparts, for A = Al and X = C. Through use of predictive phase stability calculations, we confirm all experimentally known phases to date, and also suggest a range of stable ordered and disordered hypothetical elemental combinations. Ordered o-MAX is favoured when (i) M' next to the Al-layer does not form a corresponding binary rock-salt MC structure, (ii) the size difference between M' and M'' is small, and (iii) the difference in electronegativity between M' and Al is large. Preference for chemical disorder is favoured when the size and electronegativity of M' and M'' is similar, in combination with a minor difference in electronegativity of M' and Al. We also propose guidelines to use in the search for novel o-MAX; to combine M' from group 6 (Cr, Mo, W) with M'' from groups 3 to 5 (Sc only for 312, Ti, Zr, Hf, V, Nb, Ta). Correspondingly, we suggest formation of disordered MAX phases by combing M' and M'' within groups 3 to 5 (Sc, Ti, Zr, Hf, V, Nb, Ta). The addition of novel elemental combinations in MAX phases, and in turn in their potential two-dimensional MXene derivatives, allow for property tuning of functional materials.
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http://dx.doi.org/10.1039/c9nr08675gDOI Listing
January 2020

A Tungsten-Based Nanolaminated Ternary Carbide: (W,Ti)C.

Inorg Chem 2019 Jan 4;58(2):1100-1106. Epub 2019 Jan 4.

Department of Materials Science and Engineering , Drexel University , Philadelphia , Pennsylvania 19104 , United States.

Nanolamellar transition metal carbides are gaining increasing interests because of the recent developments of their two-dimensional (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)C, synthesized by an Al-catalyzed reaction of W, Ti, and C powders at 1600 °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 /mmc) with lattice parameters, a = 3.00880(7) Å, and c = 19.5633(6) Å and a nominal chemistry of (W,Ti)C (actual chemistry, WTiC). 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.
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http://dx.doi.org/10.1021/acs.inorgchem.8b02226DOI Listing
January 2019

Origin of Chemically Ordered Atomic Laminates ( i-MAX): Expanding the Elemental Space by a Theoretical/Experimental Approach.

ACS Nano 2018 Aug 23;12(8):7761-7770. Epub 2018 Jul 23.

Thin Film Physics, Department of Physics, Chemistry and Biology (IFM) , Linköping University , SE-581 83 Linköping , Sweden.

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 (Mo M) AC (where M = 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. (MoSc)GaC and (MoY)GaC were experimentally verified, displaying the characteristic in-plane chemical order of Mo and Sc/Y and Kagomé-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.
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http://dx.doi.org/10.1021/acsnano.8b01774DOI Listing
August 2018

Electronic structure, bonding characteristics, and mechanical properties in (WSc)AlC and (WY)AlC i-MAX phases from first-principles calculations.

J Phys Condens Matter 2018 Aug 12;30(30):305502. Epub 2018 Jun 12.

Thin Film Physics Division, Department of Physics, Chemistry and Biology (IFM), Linköping University, SE-581 83 Linköping, Sweden.

With the recent discovery of in-plane chemically ordered MAX phases (i-MAX) of the general formula ([Formula: see text]) 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 (WSc)AlC and (WY)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 ) leads to reduced bonding strength for W-C and Al-Al interactions while M -C and M -Al interactions are strengthened. We also compare the Voigt-Reuss-Hill bulk, shear, and Young's moduli along the series of M   =  Cr, Mo, and W, and relate these trends to the bonding interactions. Furthermore, we find overall larger moduli for Sc-based i-MAX phases.
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http://dx.doi.org/10.1088/1361-648X/aacc19DOI Listing
August 2018

Theoretical Prediction and Synthesis of (CrZr)AlC i-MAX Phase.

Inorg Chem 2018 Jun 11;57(11):6237-6244. Epub 2018 May 11.

Department of Physics, Chemistry, and Biology , Linköping University , SE-581 83 Linköping , Sweden.

Guided by predictive theory, a new compound with chemical composition (CrZr)AlC was synthesized by hot pressing of Cr, ZrH, Al, and C mixtures at 1300 °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 (CrZr)AlC stoichiometry, with secondary CrAlC, AlZrC, and ZrC phases and a small amount of Al-Cr intermetallics. A theoretical evaluation of the (CrZr)AlC magnetic structure was performed, indicating an antiferromagnetic ground state. Also (CrHf)AlC, of the same structure, was predicted to be stable.
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http://dx.doi.org/10.1021/acs.inorgchem.8b00021DOI Listing
June 2018

W-Based Atomic Laminates and Their 2D Derivative W C MXene with Vacancy Ordering.

Adv Mater 2018 May 6;30(21):e1706409. Epub 2018 Apr 6.

Thin Film Physics Division, Department of Physics, Chemistry and Biology (IFM), Linköping University, SE-581 83, Linköping, Sweden.

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 (W M ) AC, where M = Sc, Y (W), and A = Al, Si, Ga, Ge, In, and Sn. Of over 18 compositions probed, only two-with a monoclinic C2/c structure-are predicted to be stable: (W Sc ) AlC and (W Y ) AlC and indeed found to exist. Selectively etching the Al and Sc/Y atoms from these 3D laminates results in W C-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.
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http://dx.doi.org/10.1002/adma.201706409DOI Listing
May 2018

Prediction and synthesis of a family of atomic laminate phases with Kagomé-like and in-plane chemical ordering.

Sci Adv 2017 07 19;3(7):e1700642. Epub 2017 Jul 19.

Department of Physics, Chemistry and Biology (IFM), Linköping University, SE-581 83 Linköping, Sweden.

The enigma of MAX phases and their hybrids prevails. We probe transition metal () alloying in MAX phases for metal size, electronegativity, and electron configuration, and discover ordering in these MAX hybrids, namely, (VZr)AlC and (MoY)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 Kagomé-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 2/. 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.
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http://dx.doi.org/10.1126/sciadv.1700642DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5517111PMC
July 2017

Synthesis of TiAuC, TiAuC and TiIrC by noble metal substitution reaction in TiSiC for high-temperature-stable Ohmic contacts to SiC.

Nat Mater 2017 08 1;16(8):814-818. Epub 2017 May 1.

Department of Physics, Chemistry, and Biology (IFM), Linköping University, SE-581 83 Linköping, Sweden.

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 TiAuC and TiAuC phases with up to 31% lattice swelling by a substitutional solid-state reaction of Au into TiSiC single-crystal thin films with simultaneous out-diffusion of Si. TiIrC is subsequently produced by a substitution reaction of Ir for Au in TiAuC. These phases form Ohmic electrical contacts to SiC and remain stable after 1,000 h of ageing at 600 °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.
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http://dx.doi.org/10.1038/nmat4896DOI Listing
August 2017

Two-dimensional MoC MXene with divacancy ordering prepared from parent 3D laminate with in-plane chemical ordering.

Nat Commun 2017 04 25;8:14949. Epub 2017 Apr 25.

Thin Film Physics, Department of Physics, Chemistry and Biology (IFM), Linköping University, SE-581 83 Linköping, Sweden.

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, (MoSc)AlC, with in-plane chemical ordering, and by selectively etching the Al and Sc atoms, we show evidence for 2D MoC sheets with ordered metal divacancies and high electrical conductivities. At ∼1,100 F cm, this 2D material exhibits a 65% higher volumetric capacitance than its counterpart, MoC, 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.
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http://dx.doi.org/10.1038/ncomms14949DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5413966PMC
April 2017

Dataset on the structure and thermodynamic and dynamic stability of MoScAlC from experiments and first-principles calculations.

Data Brief 2017 Feb 29;10:576-582. Epub 2016 Dec 29.

Department of Physics, Chemistry and Biology (IFM), Linköping University, Linköping SE-581 83, Sweden.

The data presented in this paper are related to the research article entitled "Theoretical stability and materials synthesis of a chemically ordered MAX phase, MoScAlC, and its two-dimensional derivate MoScC" (Meshkian et al. 2017) [1]. This paper describes theoretical phase stability calculations of the MAX phase alloy MoScAlC (=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 MoScAlC. The data is made publicly available to enable critical or extended analyzes.
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http://dx.doi.org/10.1016/j.dib.2016.12.046DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5219593PMC
February 2017

Benefits of oxygen incorporation in atomic laminates.

Authors:
Martin Dahlqvist

J Phys Condens Matter 2016 Apr 4;28(13):135501. Epub 2016 Mar 4.

Materials Modeling and Development Laboratory, National University of Science and Technology 'MISIS', 119049 Moscow, Russia.

Atomic laminates such as MAX phases benefit from the addition of oxygen in many ways, from the formation of a protective oxide surface layer with self-healing capabilities when cracks form to the tuning of anisotropic conductivity. In this paper oxygen incorporation and vacancy formation in M 2AlC (M  =  Ti, V, Cr) MAX phases have been studied using first-principles calculations where the focus is on phase stability and electronic structure for different oxygen and/or vacancy configurations. Oxygen prefers different lattice sites depending on M-element and this can be correlated to the number of available non-bonding M d-electrons. In Ti2AlC, oxygen substitutes carbon while in Cr2AlC it is located interstitially within the Al-layer. I predict that oxygen incorporation in Ti2AlC stabilizes the material, which explains the experimentally observed 12.5 at% oxygen (x  =  0.5) in Ti2Al(C(1-x)O(x)). In addition, it is also possible to use oxygen to stabilize the hypothetical Zr2AlC and Hf2AlC. Hence, oxygen incorporation may be beneficial in many ways. Not only can it make a material more stable, but it also can act as a reservoir for internal self-healing with shorter diffusion paths.
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http://dx.doi.org/10.1088/0953-8984/28/13/135501DOI Listing
April 2016

Order and disorder in quaternary atomic laminates from first-principles calculations.

Phys Chem Chem Phys 2015 Dec;17(47):31810-21

Thin Film Physics Division, Department of Physics, Chemistry and Biology (IFM), Linköping University, SE-581 83 Linköping, Sweden.

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 Tdisorder can be estimated. TiM2AlC2 (M = Cr, Mo, W) and Ti2M2AlC3 (M = Mo, W) are found with Tdisorder > 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 electronegativity 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.
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http://dx.doi.org/10.1039/c5cp06021dDOI Listing
December 2015

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 structure.

J Phys Condens Matter 2015 Nov 7;27(43):435702. Epub 2015 Oct 7.

Thin Film Physics Division, Department of Physics, Chemistry and Biology (IFM), Linköping University, SE-581 83 Linköping, Sweden.

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.
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http://dx.doi.org/10.1088/0953-8984/27/43/435702DOI Listing
November 2015

Discovery of the ternary nanolaminated compound Nb2GeC by a systematic theoretical-experimental approach.

Phys Rev Lett 2012 Jul 17;109(3):035502. Epub 2012 Jul 17.

Department of Physics, Chemistry, and Biology (IFM), Linköping University, IFM, 581 83 Linköping, Sweden.

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 ∼3.24  Å and 12.82 Å.
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http://dx.doi.org/10.1103/PhysRevLett.109.035502DOI Listing
July 2012
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