Structural, Mössbauer, and transport studies of the icosahedral quasicrystals Al₅₅Si₇Cu_25.5Fe_12.5, Al_62.5Cu_24.5Fe₁₃and the crystalline 1/1 approximant Al₅₅Si₇Cu_25.5Fe_12.5

As-quenched icosahedral Al55Si7Cu25.5Fe12.5, its 1/1 approximant of the same composition, and icosahedral Al62.5Cu24.5Fe13 alloys have been studied using x-ray diffraction, scanning transmission electron microscopy and the high-angle annular dark field technique, zero-field and in-field 57Fe Mossbauer spectroscopy, and electrical resistivity. The crystal structure of the 1/1 approximant Al55Si7Cu25.5Fe12.5 has been refined with the Rietveld method and shown to be compatible with the measured high-angle annular dark field images. The distribution of the principal component of the electric field gradient tensor has a bimodal character with a dominant negative sign in the icosahedral Al–Cu–Fe system. The local order of the Fe structural environment is compared in icosahedral Al55Si7Cu25.5Fe12.5, its 1/1 approximant, and icosahedral Al62.5Cu24.5Fe13. The average quadrupole splitting decreases with temperature as T3/2 for all alloys studied, and its value is significantly larger for the icosahedral alloys. The vibrations of the Fe atoms in the alloys studied are well described by a Debye model, with characteristic Mossbauer temperatures of 468(25), 487(19), and 455(6) K for icosahedral Al55Si7Cu25.5Fe12.5, its 1/1 approximant, and icosahedral Al62.5Cu24.5Fe13, respectively. The electrical resistivity is discussed in terms of quantum interference effects and structural disorder.