Mn/Cr isomorphic substitution in μAl 4Mn xCr 1– x phase compounds (0⩽ x⩽1)

Abstract

Neutron scattering experiments were performed on hexagonal μAl 4Mn x Cr 1– x (0⩽ x⩽1) compounds, approximants of Al–Mn and Al–Cr quasicrystalline phases, whose structures exhibit a local icosahedral order. The Mn/Cr substitution on the 10 different Wyckoff sites in the μ-phase structure is shown to be isomorphic from an analysis of partial pair structure factors and from simulations based on crystallographic data. The nature of the local icosahedral order, common to almost all the Al-rich solid phases of the Al–Mn and Al–Cr systems, is explicited. As an example, the very close similarity between measured structure factors of μAl 4Mn and λAl 4.5Mn phases can be interpreted from structural descriptions made in terms of icosahedral units where large arrangements of these units appear to be common to both phases.