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Theoretical investigation of the MXene precursors Mo_xV_4-xAlC₃ (0 ≤ x ≤ 4).

ABSTRACT: By first-principles total-energy calculations, we investigated the thermodynamic stability of the MAX solid solution Mo_xV_4-xAlC₃ in the 0 ≤ x ≤ 4 range. Results evidence that lattice parameter a increases as a function of Mo content, while the c parameter reaches its maximum expansion at x = 2.5. After that, a contraction is noticed. Mo occupies V_I sites randomly until the out-of-plane ordered Mo₂V₂AlC₃ alloy is formed. We employed the Defect Formation Energy (DFE) formalism to evaluate the thermodynamic stability of the alloys. Calculations show five stable compounds. At V-rich conditions and from Mo-rich to Mo-moderated conditions, the pristine V₄AlC₃ MAX is stable. In the region of V-poor conditions, from Mo-rich to Mo-moderated growth conditions, the solid solutions with x = 0.5, 1, and 1.5 and the o-MAX Mo₂V₂AlC₃ are thermodynamically stable. The line profiles of the Electron Localization Function and Bader charge analysis show that the V-C interaction is mainly ionic, while the Mo-C is covalent. Also, the exfoliation energy to obtain a MXene layer is ~ 0.4 eV/Å². DFE also shows that MXenes exfoliated from the MAX phase with the same Mo content and atomic arrangement are thermodynamically stable. Our results get a deeper atomic scale understanding of the previously reported experimental evidence.

SUBMITTER: Moreno-Armenta MG

PROVIDER: S-EPMC9968326 | biostudies-literature | 2023 Feb

REPOSITORIES: biostudies-literature

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Theoretical investigation of the MXene precursors MoxV4-xAlC3 (0 ≤ x ≤ 4).

Moreno-Armenta Ma Guadalupe MG Guerrero-Sánchez J J Gutiérrez-Ojeda S J SJ Fernández-Escamilla H N HN Hoat D M DM Ponce-Pérez R R

Scientific reports 20230225 1

By first-principles total-energy calculations, we investigated the thermodynamic stability of the MAX solid solution MoxV4-xAlC3 in the 0 ≤ x ≤ 4 range. Results evidence that lattice parameter a increases as a function of Mo content, while the c parameter reaches its maximum expansion at x = 2.5. After that, a contraction is noticed. Mo occupies VI sites randomly until the out-of-plane ordered Mo2V2AlC3 alloy is formed. ...[more]

PMID: 36841864

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Project description:The realization of the broad range of application of MXenes relies on the successful and reproducible synthesis of quality materials of tailored properties. To date, most MXenes have been produced making use of acid-based etching methods, yet an in-depth understanding of etching processes is lacking. Herein, we have engaged in a comprehensive study of the multiple variables involved in the synthesis of V2CTx with focus on the properties of etched materials. Two main sets of experiments were considered, each using a different V2AlC precursor and a range of synthesis variables including reaction time and temperature, mixing rate, and type of acid. Correlations of synthesis conditions-materials properties were investigated using a broad range of characterization techniques including analytical methods, scanning and transmission electron microscopy, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Findings indicated the crucial relevance of properties of the MAX precursor such as elemental composition, particle size, and crystal structure on etching processes and properties of etched materials. Particularly, depending on the MAX precursor, two etching patterns were identified, core-shell and plate-by-plate, the latter describing a more efficient etching. Combined studies of elemental composition, crystal structure, and yield quantification allowed us to evaluate the effectiveness of etching processes. XRD studies revealed key crystal-structure-type of acid correlations showing advantages of using a HF/HCl mix over only HF. Analytical methods XRD and XPS delivered insights into undergoing chemical processes and their influence on bulk and surface chemistry of etched materials. The relevance for reaction kinetics of highly correlated variables such as reaction vessel dimensions, mixing efficiency, and reaction temperature was recognized. For the first time, a MXene synthesis has been investigated comprehensively highlighting its multivariable nature and the high variable intercorrelation, opening up venues for further investigation on MAX and MXene synthesis.

Dataset Information

Theoretical investigation of the MXene precursors Mo_xV_4-xAlC₃ (0 ≤ x ≤ 4).

Publications

Theoretical investigation of the MXene precursors Mo<sub>x</sub>V<sub>4-x</sub>AlC<sub>3</sub> (0 ≤ x ≤ 4).

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