Observation of Substitutional Site Preference in a Quasicrystal and Implication on Local Structure

A combination of magnetic susceptibility and Mossbauer measurements on quasicrystalline i­ Ah4Mn2o-xFexSi6 (0.02 ~ x ~ 7.5) establishes that Mn atoms in i-Ab4Mn2oSi6 occupy two distinct classes of sites, and that Fe substitutes for only one of them. The two classes are distinguished by the possession or otherwise of a localized magnetic moment. The data are consistent with a structure of in­ terconnecting Mackay icosahedra (MI) in which localized moments are possessed only by Mn atoms ad­ jacent to "broken" MI connections. The implied connectivity of the resulting MI network is close to that anticipated for a packing of MI on a three-dimensional Penrose-tile lattice.