Local Structure at Mn Sites in Icosahedral Mn-Al Quasicrystals

Abstract

Extended x-ray-absorption fine-structure measurements have been made at the Mn $K$ edge of quasicrystalline and crystalline forms of an ${\mathrm{Al}}_6$Mn alloy. Two different quasicrystalline Mn sites are discerned to be populated in the ratio of $\tau$, the golden mean, within experimental error. The more populous site is similar to that in the crystal but with bond-angle distortions and elimination of an unusually short Al-Mn bond, while the other site has additional bond-stretching distortions. The measurements together with density measurements indicate that the volume per Mn site is independent of the type of site.