A New Structural Study for an Old Quasicrystal

Abstract
In this paper, we have described the experimental evidence for the polyhedral order in metastable Al-Mn alloy (icosahedral phase). We have used the anomalous diffractometry technique to identify the X-ray patterns of this alloy. For the first time, the radial distribution function of the diffuse rings scattered by this alloy is obtained by applying this new technique. Unlike previous methods used for interpreting the X-ray patterns of this phase, we have introduced a new method of separation for interpreting X-ray patterns. The X-ray diffraction pattern has been numerically resolved into a broad diffuse halo and sharp lines. Using this procedure the correlation position was deduced from a high quality interference function. We have not been able to explain either the origin of the sharp lines or the relationship of the two parts responsible for the lines and rings. In order to explain the above we need an appropriate geometrical model and some structural information on the medium range order of the atoms causing scattered rings. This information is contained in the partial pair-pair correlation function of the coherent background. The result of this work may be of aid in order to comprehend the "genetic" relationship between the structure of the crystalline, amorphous FK phases and this new metastable alloy or icosahedral phase.