Growth and thermal stability of (V,Al)2Cx thin films

Vanadium (V)–aluminum (Al)–carbon (C) thin films were deposited on Al2O3$(11\mathop 2\limits^ - 0)$ substrates at 500 °C by direct current magnetron sputtering using a powder metallurgical composite target with 2:1:1 MAX phase stoichiometry. Transmission electron microscopy (TEM) and x-ray diffraction results suggest that a hexagonal Al-containing vanadium carbide solid solution (V,Al)2Cx was formed. The films exhibited a strong basal plane texture. The lattice parameter of the hexagonal solid solution was dependent on the annealing temperature: the c lattice parameter decreased by 3.45% after annealing for 1 h at 750 °C compared to the as-deposited film. Based on the comparison between experimental and theoretical lattice parameter data, it is reasonable to assume that this annealing-induced change in lattice parameter is a consequence of atomic ordering. Meanwhile, the formation of V2AlC MAX phase was observed at 650 °C and phase-pure V2AlC was obtained at 850 °C. TEM images support the notion that V2AlC forms by nucleation and growth.