scispace - formally typeset
Search or ask a question
Journal ArticleDOI

Theoretical stability and materials synthesis of a chemically ordered MAX phase, Mo2ScAlC2, and its two-dimensional derivate Mo2ScC2 MXene

15 Feb 2017-Acta Materialia (Pergamon)-Vol. 125, pp 476-480
TL;DR: In this paper, a MAX phase alloy with out-of-plane chemical order, Mo2ScAlC2, was presented, with a formation enthalpy of −−24meV/atom.
About: This article is published in Acta Materialia.The article was published on 2017-02-15 and is currently open access. It has received 155 citations till now. The article focuses on the topics: Phase (matter) & High-resolution transmission electron microscopy.

Summary (2 min read)

1. Introduction

  • It has been about six decades since Nowotny et al. discovered a family of laminated material called H-phases [1].
  • To date, more than 70 MAX phases have been synthesized in both bulk and thin film form.
  • The first Mo2C MXene was reported in 2015 [18, 19], and has since been found to have high potential for e.g. energy storage, in particular for electrode material in e.g. Li-ion batteries [20].
  • Structural and compositional characterization show separation of the elements into individual atomic layers.

2. Computational details

  • First-principles calculations were performed by means of density functional theory (DFT) and the projector augmented wave method [23, 24] as implemented within the Vienna abinitio simulation package (VASP) [25-27].
  • The authors adopted the non-spin polarized generalized gradient approximation (GGA) as parameterized by Perdew-Burke-Ernzerhof (PBE) [28] for treating electron exchange and correlation effects.
  • These are modelled using the special quasi-random structure (SQS) method [30, 31] on supercells of 4×4×1 M3AX2 unit cells, with a total of 96 M-sites, respectively.
  • Evaluation of phase stability was performed by identifying the set of most competing phases at a given composition, using a linear optimization procedure [31, 32] including all competing phases in the system.
  • This gives an estimate above which temperature the disordered structure is energetically favorable as compared to the ordered structure.

3. Experimental details

  • These powders were mixed in an agate mortar and placed in a covered Al2O3 crucible, which was inserted in a tube furnace.
  • Both MAX and MXene samples were also characterized by using the Linköping double Cs corrected FEI Titan3 60– 300 operated at 300 kV, equipped with the Super-X EDX system to perform atomic structural analysis.
  • The suspension was afterwards filtered and dispersed in water ~10 times in order to remove all the remaining acid and the reaction products.
  • Subsequent intercalation of the MXene sheets were realized by adding ~0.1g of the powder in ~1ml of an organic base, tetrabutylammonium hydroxide , and shaking it manually for ~5 min.

4. Results and discussion

  • For Mo2ScAlC2 and Sc2MoAlC2, six different layer sequences were considered, see Anasori et al. [37] for layer stacking definitions.
  • The in-plane and out-of-plane lattice parameters, a and c, determined from Rietveld refinement, are 3.03 and 18.77 Å, respectively.
  • Furthermore, if the M element closest to the Al layer has larger electronegativity than Al, this results in fewer electrons available for populating antibonding Al-Al orbitals, which is energetically expensive [6].
  • X-ray diffractograms of the Mo2ScAlC2 MAX powder and its corresponding MXene, Mo2ScC2, after etching and intercalation, is shown in Fig.
  • The etching is not fully completed as the scan for the MXene also contains residual Mo2ScAlC2.

5. Conclusions

  • The authors have theoretically predicted the existence of a new quaternary MAX phase alloy with out-of-plane chemical order, Mo2ScAlC2, with a Sc atomic layer sandwiched between two Mo-C layers.
  • The prediction has been experimentally verified through bulk synthesis and materials characterization, primarily from high resolution STEM with EDX elemental mapping.
  • The a and c lattice parameters determined using Rietveld refinement are 3.03 and 18.77 Å, respectively.
  • Furthermore, the MAX phase has been converted into twodimensional MXene by selective etching of Al.
  • The resulting MXene, Mo2ScC2, is the first MXene to date comprising Sc. 12.

Did you find this useful? Give us your feedback

Citations
More filters
Journal ArticleDOI
TL;DR: In this paper , a review of the existing state-of-the-art regarding transition metal carbides' covalent functionalization with a particular emphasis on tribological properties and needs is presented.

16 citations

Journal ArticleDOI
TL;DR: In this article, the phase stability and Mo/Sc intermixing on the M site in the chemically ordered quaternary phase was explored, with the highest crystal quality obtained for the ideal Mo:Sc ratio of 2:1 (predicted as the most stable).
Abstract: Research on low-dimensional materials has increased drastically in the last decade, with the discovery of two-dimensional transition metal carbides and nitrides (MXenes) produced by atom-selective chemical etching of laminated parent ${M}_{n+1}A{X}_{n}$ (MAX) phases. Here, we apply density functional theory and subsequent materials synthesis and analysis to explore the phase stability and Mo/Sc intermixing on the M site in the chemically ordered quaternary $i\ensuremath{-}\mathrm{MAX}$ phase (${\mathrm{Mo}}_{x}{\mathrm{Sc}}_{1\ensuremath{-}x}{)}_{2}\mathrm{AlC}$. Transmission electron microscopy confirms the theoretical predictions of preferential in-plane ordering of Mo and Sc, with the highest crystal quality obtained for the ideal Mo:Sc ratio of 2:1 (predicted as the most stable), as well as a retained $i\ensuremath{-}\mathrm{MAX}$ structure even for an increased relative Sc content, with Sc partially occupying Mo sites. The results are supported by refined neutron diffraction data, which show space group $C2/c$ (no. 15), and a C occupancy of 1. Subsequent chemical etching produces MXene for $x=0.66$, while for $x=0.33$ and 0.5 no MXene is observed. These results demonstrate that a precise control of the $i\ensuremath{-}\mathrm{MAX}$ composition is crucial for derivation of MXene, with a MXene quality optimized for a Mo:Sc ratio of 2:1 with minimal intermixing between Mo and Sc.

15 citations

Journal ArticleDOI
Zou Xiangda1, Li Guorong1, Wang Qifan1, Dian Tang1, Bo Wu1, Xin Wang1 
TL;DR: In this paper, the properties of two-dimensional Cr-group MXenes were explored using atom-scale analyses, and it was concluded that Cr2CT2 compounds are more stable when spin polarized depending on the case.

15 citations

Journal ArticleDOI
TL;DR: In this paper , transition metal carbides and nitrides (MXenes), a newly emerging class of 2D layered materials, has gained tremendous attention as a noble metal-free co-catalyst for boosting photoreactivity due to its extraordinary characteristics like elemental abundance, excellent electrical conductivity, abundant surface functional groups, unique hydrophilic behavior and flexible modulation of chemical composition.

15 citations

Journal ArticleDOI
01 Jul 2021-Carbon
TL;DR: In this paper, the crystallographic structure of rare-earth-contained (Mo2/3R1/3)2AlC i-MAX phases has been verified to be C2/c monoclinic.

14 citations

References
More filters
Journal ArticleDOI
TL;DR: A simple derivation of a simple GGA is presented, in which all parameters (other than those in LSD) are fundamental constants, and only general features of the detailed construction underlying the Perdew-Wang 1991 (PW91) GGA are invoked.
Abstract: Generalized gradient approximations (GGA’s) for the exchange-correlation energy improve upon the local spin density (LSD) description of atoms, molecules, and solids. We present a simple derivation of a simple GGA, in which all parameters (other than those in LSD) are fundamental constants. Only general features of the detailed construction underlying the Perdew-Wang 1991 (PW91) GGA are invoked. Improvements over PW91 include an accurate description of the linear response of the uniform electron gas, correct behavior under uniform scaling, and a smoother potential. [S0031-9007(96)01479-2] PACS numbers: 71.15.Mb, 71.45.Gm Kohn-Sham density functional theory [1,2] is widely used for self-consistent-field electronic structure calculations of the ground-state properties of atoms, molecules, and solids. In this theory, only the exchange-correlation energy EXC › EX 1 EC as a functional of the electron spin densities n"srd and n#srd must be approximated. The most popular functionals have a form appropriate for slowly varying densities: the local spin density (LSD) approximation Z d 3 rn e unif

146,533 citations


"Theoretical stability and materials..." refers methods in this paper

  • ...We adopted the non-spin polarized generalized gradient approximation (GGA) as parameterized by Perdew-Burke-Ernzerhof (PBE) [28] for...

    [...]

  • ...We adopted the non-spin polarized generalized gradient approximation (GGA) as parameterized by Perdew-Burke-Ernzerhof (PBE) [28] for treating electron exchange and correlation effects....

    [...]

Journal ArticleDOI
TL;DR: An efficient scheme for calculating the Kohn-Sham ground state of metallic systems using pseudopotentials and a plane-wave basis set is presented and the application of Pulay's DIIS method to the iterative diagonalization of large matrices will be discussed.
Abstract: We present an efficient scheme for calculating the Kohn-Sham ground state of metallic systems using pseudopotentials and a plane-wave basis set. In the first part the application of Pulay's DIIS method (direct inversion in the iterative subspace) to the iterative diagonalization of large matrices will be discussed. Our approach is stable, reliable, and minimizes the number of order ${\mathit{N}}_{\mathrm{atoms}}^{3}$ operations. In the second part, we will discuss an efficient mixing scheme also based on Pulay's scheme. A special ``metric'' and a special ``preconditioning'' optimized for a plane-wave basis set will be introduced. Scaling of the method will be discussed in detail for non-self-consistent and self-consistent calculations. It will be shown that the number of iterations required to obtain a specific precision is almost independent of the system size. Altogether an order ${\mathit{N}}_{\mathrm{atoms}}^{2}$ scaling is found for systems containing up to 1000 electrons. If we take into account that the number of k points can be decreased linearly with the system size, the overall scaling can approach ${\mathit{N}}_{\mathrm{atoms}}$. We have implemented these algorithms within a powerful package called VASP (Vienna ab initio simulation package). The program and the techniques have been used successfully for a large number of different systems (liquid and amorphous semiconductors, liquid simple and transition metals, metallic and semiconducting surfaces, phonons in simple metals, transition metals, and semiconductors) and turned out to be very reliable. \textcopyright{} 1996 The American Physical Society.

81,985 citations


"Theoretical stability and materials..." refers methods in this paper

  • ...First-principles calculations were performed by means of density functional theory (DFT) and the projector augmented wave method [23, 24] as implemented within the Vienna abinitio simulation package (VASP) [25-27]....

    [...]

Journal ArticleDOI
Peter E. Blöchl1
TL;DR: An approach for electronic structure calculations is described that generalizes both the pseudopotential method and the linear augmented-plane-wave (LAPW) method in a natural way and can be used to treat first-row and transition-metal elements with affordable effort and provides access to the full wave function.
Abstract: An approach for electronic structure calculations is described that generalizes both the pseudopotential method and the linear augmented-plane-wave (LAPW) method in a natural way. The method allows high-quality first-principles molecular-dynamics calculations to be performed using the original fictitious Lagrangian approach of Car and Parrinello. Like the LAPW method it can be used to treat first-row and transition-metal elements with affordable effort and provides access to the full wave function. The augmentation procedure is generalized in that partial-wave expansions are not determined by the value and the derivative of the envelope function at some muffin-tin radius, but rather by the overlap with localized projector functions. The pseudopotential approach based on generalized separable pseudopotentials can be regained by a simple approximation.

61,450 citations


"Theoretical stability and materials..." refers methods in this paper

  • ...First-principles calculations were performed by means of density functional theory (DFT) and the projector augmented wave method [23, 24] as implemented within the Vienna abinitio simulation package (VASP) [25-27]....

    [...]

Journal ArticleDOI
TL;DR: In this paper, the formal relationship between US Vanderbilt-type pseudopotentials and Blochl's projector augmented wave (PAW) method is derived and the Hamilton operator, the forces, and the stress tensor are derived for this modified PAW functional.
Abstract: The formal relationship between ultrasoft (US) Vanderbilt-type pseudopotentials and Bl\"ochl's projector augmented wave (PAW) method is derived. It is shown that the total energy functional for US pseudopotentials can be obtained by linearization of two terms in a slightly modified PAW total energy functional. The Hamilton operator, the forces, and the stress tensor are derived for this modified PAW functional. A simple way to implement the PAW method in existing plane-wave codes supporting US pseudopotentials is pointed out. In addition, critical tests are presented to compare the accuracy and efficiency of the PAW and the US pseudopotential method with relaxed core all electron methods. These tests include small molecules $({\mathrm{H}}_{2}{,\mathrm{}\mathrm{H}}_{2}{\mathrm{O},\mathrm{}\mathrm{Li}}_{2}{,\mathrm{}\mathrm{N}}_{2}{,\mathrm{}\mathrm{F}}_{2}{,\mathrm{}\mathrm{BF}}_{3}{,\mathrm{}\mathrm{SiF}}_{4})$ and several bulk systems (diamond, Si, V, Li, Ca, ${\mathrm{CaF}}_{2},$ Fe, Co, Ni). Particular attention is paid to the bulk properties and magnetic energies of Fe, Co, and Ni.

57,691 citations


"Theoretical stability and materials..." refers methods in this paper

  • ...First-principles calculations were performed by means of density functional theory (DFT) and the projector augmented wave method [23, 24] as implemented within the Vienna abinitio simulation package (VASP) [25-27]....

    [...]

Journal ArticleDOI
TL;DR: In this article, a method for generating sets of special points in the Brillouin zone which provides an efficient means of integrating periodic functions of the wave vector is given, where the integration can be over the entire zone or over specified portions thereof.
Abstract: A method is given for generating sets of special points in the Brillouin zone which provides an efficient means of integrating periodic functions of the wave vector. The integration can be over the entire Brillouin zone or over specified portions thereof. This method also has applications in spectral and density-of-state calculations. The relationships to the Chadi-Cohen and Gilat-Raubenheimer methods are indicated.

51,059 citations


"Theoretical stability and materials..." refers methods in this paper

  • ...was used and for sampling of the Brillouin zone we used the Monkhorst-Pack scheme [29]....

    [...]

Frequently Asked Questions (2)
Q1. What are the future works in "Theoretical stability and materials synthesis of a chemically ordered max phase, mo2scalc2, and its two-dimensional derivate mo2scc2 mxene" ?

The authors have theoretically predicted the existence of a new quaternary MAX phase alloy with out-of-plane chemical order, Mo2ScAlC2, with a Sc atomic layer sandwiched between two Mo-C layers. 

The authors 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.