title: High-Throughput Survey of Ordering Configurations in MXene Alloys Across Compositions and Temperatures.
abstract: 2D transition metal carbides and nitrides known as MXenes are gaining increasing attention. About 20 of them have been synthesized (more predicted) and their applications in fields ranging from energy storage and electromagnetic shielding to medicine are being explored. To facilitate the search for double-transition-metal MXenes, we explore the structure-stability relationship for 8 MXene alloy systems, namely, (V1-xMox)3C2, (Nb1-xMox)3C2, (Ta1-xMox)3C2, (Ti1-xMox)3C2, (Ti1-xNbx)3C2, (Ti1-xTax)3C2, (Ti1-xVx)3C2, and (Nb1-xVx)3C2,with 0 ≤ x ≤ 1, using high-throughput computations. Starting from density-functional theory calculated formation energies, we used the cluster expansion method to build quick-to-compute interactions, enabling us to scan through the formation energies of millions of alloying configurations. For the Mo-rich MXenes, (M11-xMox)3C2(where M1: Ti, V, Nb, Ta) Mo atoms prefer to occupy the surface layers, and ordering persists to high temperatures, based on our Monte Carlo simulations. When Ti is alloyed with Nb or Ta, in the Ti-rich MXenes, Ti atoms prefer the surface layers (e.g., Ti-C-Nb-C-Ti sequence), and in the Nb- or Ta-rich MXenes, Ti occupies only one surface layer and the other two layers are Nb or Ta (e.g., Ti-C-Nb-C-Nb), exhibiting asymmetric ordering. However, alloying Ti with V results in solid solutions across all compositions. (Nb1-xVx)3C2phase separates at lower temperatures but forms solid solutions at synthesis temperatures. Postsynthesis annealing at moderate temperatures (800 to 1000 K) increases the ordering for all the compositions. Lastly, by investigating the stability of their precursor MAX phases and surface-terminated MXenes, we discuss the synthesis possibilities of highly ordered MXenes.
authors.affiliation: Institute of High Performance Computing, Agency for Science, Technology and Research , 1 Fusionopolis Way, #16-16 Connexis, Singapore 138632, Singapore.
authors.forename: Teck Leong
authors.identifier: 0000-0002-7089-8966
authors.initials: TL
authors.lastname: Tan
authors.affiliation: Institute of High Performance Computing, Agency for Science, Technology and Research , 1 Fusionopolis Way, #16-16 Connexis, Singapore 138632, Singapore.
authors.forename: Hong Mei
authors.initials: HM
authors.lastname: Jin
authors.affiliation: Institute of High Performance Computing, Agency for Science, Technology and Research , 1 Fusionopolis Way, #16-16 Connexis, Singapore 138632, Singapore.
authors.forename: Michael B
authors.initials: MB
authors.lastname: Sullivan
authors.affiliation: A.J. Drexel Nanomaterials Institute, and Department of Materials Science & Engineering, Drexel University , Philadelphia, Pennsylvania 19104, United States.
authors.forename: Babak
authors.initials: B
authors.lastname: Anasori
authors.affiliation: A.J. Drexel Nanomaterials Institute, and Department of Materials Science & Engineering, Drexel University , Philadelphia, Pennsylvania 19104, United States.
authors.forename: Yury
authors.identifier: 0000-0001-9423-4032
authors.initials: Y
authors.lastname: Gogotsi
keywords: 2D material; MXene; alloy; density functional theory; ordering