Synthesis and characterization of a new out-of-plane ordered double-transition-metal MAX phase, Mo2VAlC2, and its two-dimensional derivate Mo2VC2Tx 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 Mo2VC2Tx MXene has been successfully realized by etching the Al layer of Mo2VAlC2 with hydrofluoric acid. The chemical composition and microstructure of Mo2VC2Tx are inspected with SEM and EDX. The resulting multilayer and intercalated Mo2VC2Tx 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.