Local environment of iron sites in icosahedral ${\mathrm{Al}}_{65}$${\mathrm{Cu}}_{20}$${\mathrm{Fe}}_{15}$

A novel icosahedral alloy, ${\mathrm{Al}}_{65}$ ${\mathrm{Cu}}_{20}$ ${\mathrm{Fe}}_{15}$, produced in both a thermodynamically metastable and stable phase, has been studied with ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ Mössbauer spectroscopy, x-ray diffraction, and differential thermal analysis. It was found that the Mössbauer spectrum of either phase can be successfully analyzed in terms of a distribution of quadrupole-splitting magnitudes. This is interpreted as evidence for a continuous distribution of iron sites. The similarities of Mössbauer parameters of both phases indicate that a high degree of atomic disorder is an intrinsic property of icosahedral materials. Critical examination of previous Mössbauer studies of icosahedral materials together with other published experimental data show that the assertion of two distinct transition-metal sites in these materials is unfounded. Our results can be interpreted in terms of the distorted-icosahedral quasicrystal model.