Synthesis and characterization of a new out-of-plane ordered double-transition-metal MAX phase, Mo₂VAlC₂, and its two-dimensional derivate Mo₂VC₂T_x MXene

Herein we demonstrate the synthesis of a new out-of-plane ordered double-transition-metal MAX phase known as Mo₂VAlC₂. Annealing the elemental powder mixture at 1540 °C with 2.0Mo: 1.0 V: 1.3Al: 1.8C results in a high yield of 91.2 wt% for Mo₂VAlC₂. The crystal structure of Mo₂VAlC₂ is determined using Rietveld refinement of powder XRD, and which crystalizes into a hexagonal lattice structure with space group P6₃/mmc. Employing the double spherical aberration corrected transmission electron microscopy, we confirm its chemically ordering behavior of one V layer sandwiched between two Mo layers. Additionally, its two-dimensional derivative Mo₂VC₂T_x MXene has been successfully realized by etching the Al layer of Mo₂VAlC₂ with hydrofluoric acid. The chemical composition and microstructure of Mo₂VC₂T_x are inspected with SEM and EDX. The resulting multilayer and intercalated Mo₂VC₂T_x exhibit the characteristic accordion-like and paper-like appearances, respectively. This work further expands the diversity of chemically ordered double-transition-metal MAX and MXene families.