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

TLDR: 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.

Figures

Fig. 3. XRD scan of (a) Mo2ScAlC2 MAX powder (b) Mo2ScC2 MXene, and (c) MXene after intercalation in TBAOH solution. The c lattice parameters for these samples are 18.77, 24.6 and 34.8 Å, respectively.

Fig. 2. (a) HR(S)TEM micrograph shows the laminated structure of the MAX phase along the [112�0] zone axis. (b) The overlapping EDX elemental map for Mo, Sc and Al reveals the chemically ordered distribution of these elements within the sample.

Fig. 4. (a) An overview STEM micrograph of MoScC MXene sample; (b) left: HRSTEM image, middle: the corresponding EDX map and the HRSTEM image superimposed with the EDX map; (c) a line scan of the EDX map shown by the above light blue arrow.

Fig. 1. XRD analysis; measured scan (red), and the calculated pattern (black) using Rietveld refinement. The blue line is the difference between the two. The Bragg positions for the main phase, Mo2ScAlC2 (top) and the included phases, Mo3Al2C, Mo2C, Al2O3 and Mo3Al can also be seen in the figure.

Frequently asked questions

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. 

Q2. What are the contributions in "Theoretical stability and materials synthesis of a chemically ordered max phase, mo2scalc2, and its two-dimensional derivate mo2scc2 mxene" ?

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.