Thermally induced substitutional reaction of Fe into Mo₂GaC thin films

Abstract

The first Fe-based MAX phase is realized by solid-state substitution reaction of an Fe/Au/Mo 2 GaC thin-film diffusion couple, as determined by X-ray diffraction and scanning transmission electron microscopy. Chemical analysis together with elemental mapping reveals that as much as 50 at.% Fe on the A site can be obtained by thermally induced Au and Fe substitution for Ga atomic layers in Mo 2 GaC. One-sixth of the original Ga is also replaced by Au atoms. When annealing Mo 2 GaC thin films covered with Fe only, the Mo 2 GaC phase remains intact, that is, Au acts as a catalyst for the substitution reaction. IMPACT STATEMENT The first direct evidence showing Fe-containing MAX phase, Mo 2 AC, with Fe ∼ 50 at.% on the A sites is presented, synthesized by thermally induced Fe and Au substitution reaction catalyzed by Au.

Synthesis of MAX phases Nb2CuC and Ti2(Al0.1Cu0.9)N by A-site replacement reaction in molten salts

“…As can be observed in both images, one darker layer (the A elements) interleaves two adjoining brighter layers of Nb with larger atomic mass. The presented images are similar to STEM images of other M2AX phases having the characteristic zig-zag stacking of the 211 Mn+1Xn layers[6,12]. InFigure 4(c), the atomic-resolved EDS element mapping and line-scan of Nb-Lα and Cu-Kα further identified the atom position of Cu, all at A sites, corroborating the synthesis of Nb2CuC MAX phase through a replacement reaction, to form a MAX phase with only Cu on the A site.…”

“…By now, more than 80 members of ternary MAX compositions have been discovered [5]. Recent studies have also demonstrated that the A-site element in MAX phases can be a late transition metal (e.g., Au, Ir, Zn, Fe and Cu) [6][7][8][9][10][11][12][13]. Transition metals have distinct properties different from other A-group elements due to their large d electron orbits.…”

Near-room temperature ferromagnetic behavior of single-atom-thick 2D iron in nanolaminated ternary MAX phases

“…Recently, in order to overcome the interference of competing phases on the formation of targeting MAX phases, an isomorphous replacement approach was developed. This replacement strategy takes advantage of chemically stable Mn+1Xn slabs, with a full replacement reaction of the A atoms between these slabs in nanolaminated MAX phases by annealing in contact with a metal reservoir [7][8][9][10] , or a Lewis acid molten salt [11][12][13] to achieve atomic-layer-exchange in a confined single-atom-thick 2D space. Since H. Notwotny et al reported the first MAX phase in the 1960's [14][15] , this isomorphous replacement strategy has resulted in groundbreaking new ternary MAX phases (such as Ti3AuC2 [7] , Ti3IrC2 [7] , Mo2AuC [9] , Ti3ZnC2 [11] , Ti2ZnC [11] , V2ZnC [11] , Ti2ZnN [11] and Nb2CuC [13] ).…”

Magnetic properties and structural characterization of layered (Cr0.5Mn0.5)2AuC synthesized by thermally induced substitutional reaction in (Cr0.5Mn0.5)2GaC

“…30,31 A substitutional reaction involving an Fe + Au alloy has also been used to introduce Fe into the MAX phase A-layer. 18 Here, we report on synthesis and characterization of a novel magnetic MAX phase, (Cr 0.5 Mn 0.5 ) 2 AuC obtained from the substitutional solid state reaction between a (Cr 0.5 Mn 0.5 ) 2 GaC thin film and an Au-capping layer. The discovery of the (Cr 0.5 Mn 0.5 ) 2 AuC phase is not only a new material, but more importantly it provides a direct method for modifying the magnetic properties of inherently nanolaminated carbides with different A elements.…”

“…15 Experimental studies have also been done on attaining magnetic MAX phases by alloying Fe on the M sites 16,17 or the A sites. 18 For a more comprehensive summary, please see the review in Ref. 19.…”