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The Zn–Sc–Fe icosahedral quasicrystal and its 1/1 crystal approximant have been studied with 57Fe Mossbauer spectroscopy at room temperature. The spectra for the two phases exhibit substantially different features, indicating largely different local atomic environments in the two phases. This is in contrast to the results previously reported for the Al–Cu–Fe(–Si) system, in which the icosahedral phase and its crystal approximants show similar features in Mossbauer spectra, indicating similar local atomic environments. Possible Fe sites in the Zn–Sc–Fe approximant phase are discussed on the basis of the crystal structure determined previously.

International audience; Using in situ x-ray scattering and synchrotron radiation, we have experimentally elucidated the mechanism of the cubic to monoclinic phase transition in the Zn6Sc 1/1 approximant to an icosahedral quasicrystal. The high-temperature cubic phase is described as a bcc packing of a large Tsai-type icosahedral cluster whose center is occupied by an orientationally disordered Zn-4 tetrahedron. A clear monoclinic distortion has been found to take place within 2 K around T-c = 157 K, in excellent agreement with the observed anomalies in the electrical resistivity and heat capacity. Also, a rapid variation of the super-structure reflection intensity is observed. The low-temperature monoclinic phase, as determined by single-crystal x-ray diffraction at 40 K, has been confirmed to consist of ordered Zn-4 tetrahedra, oriented in an anti-parallel way along the [(1) over bar 01] direction. Above T-c, a diffuse scattering signal is observed at the position of the super-structure reflections, which evidences that a short-range ordering of the Zn-4 tetrahedra takes place. In a way similar to a second-order phase transition, the correlation length describing this short-range ordering increases rapidly when the temperature diminishes and almost diverges when the temperature is close to T-c, going from 200 angstrom at 220 K to reach the very large value of 1200 angstrom at 161 K. Finally, using single-crystal x-ray diffraction, the atomic structure of the low-temperature monoclinic super-structure (space group C2/c) could be solved. The ordering of the Zn-4 tetrahedra is accompanied by a strong distortion of the surrounding shells