Structure and composition of Al(Si)CuFe approximant thin films formed by Si substrate diffusion

Multilayered Al/Cu/Fe thin films with composition close to the quasicrystalline phase have been prepared by magnetron sputtering. Annealing at 600 °C yields a homogeneous film of the cubic α-approximant phase by Si substrate diffusion, which prevents the formation of the quasicrystalline phase. After 4 h annealing the film contained 8 at.% Si, which corresponds to the expected value of the α-approximant. The amount of Si in the films was found to slowly increase to ~ 12 at.% during continued annealing (64 h) while the α-approximant phase was retained. The lattice parameter was found to continuously decrease as Al became substituted with Si. The film is observed to be polycrystalline with individual grains being strained in varying magnitude, and with no preferential orientation relationship to the substrate or each other.