Crystalline and quasi-crystalline phases of the Al-Si-Mn system: a comparison of the57Fe electric-field-gradient properties

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Abstract
The authors present here the determination of the distribution P(q) of the electric field gradient in Fe-doped Al-Si-Mn icosahedral and decagonal quasi-crystals and in the related crystalline phases, using in-field Mossbauer effect spectroscopy. The distribution P(q) for the quasi-crystalline compounds shows a bimodal, nearly symmetric form with P(0) approximately=0 and equal averages over positive and negative q=1/2eQVzz, -(q-) approximately=(q+) and equal standard deviations: sigma - approximately= sigma +. The results for the majority sign of the distribution P(q) will be compared to the results for the cubic, hexagonal and orthorhombic compounds. The results show that there are similarities in the local order between the icosahedral quasi-crystalline phase and the hexagonal phase. No evidence is found for a two-site model, which has recently been proposed by other authors.