X-ray structural analysis of three dimensional quasicrystals

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Among the three dimensional quasicrystals, so called Mackay type and TC type quasicrystals are settling to the understanding of their atomic structures to be quasiperiodic arrangements of the atomic clusters with icosahedral symmetry, which are typically seen in QCIC (Quasiperiodic Configuration of Icosahedral Clusters) model proposed by the present group. The structures of so called F-type quasicrystals, which are recently discovered three dimensional quasicrystals, are still remained unknown.The objective of the present study is to analyze the atomic structures of the F-type quasicrystals in Al-Cu-Fe, Al-Cu-Ru and Al-Pd-Mn alloy systems in comparison with the structure of conventional Mackey type quasicrystals and to construct the structural models.The X-ray diffraction experiments were performed in Photon Factory of KEK. The diffraction profile was measured with powder samples. In the case of Al-Cu-Ru and Al-Pd-Mn systems, X-ray abnormal scattering was also measured at Ru edge and P … More d edge, respectively, in order to obtain the environmental structures around Ru and Pd atoms. Single crystals of the Al-Pd-Mn system were successfully grown by Bridgeman method and the diffraction was measured also for the single crystal.The X-ray diffraction profiles present the extra peaks with odd indices that come from the ordered structures in the quasicrystals. The total pair distribution functions and the environmental pair distribution functions were calculated from the profiles. The detailed analysis revealed that the F-type quasicrystals have very similar local structures to those in the conventional Mackay type quasicrystals, which indicates that the F-type quasicrystals are also consist of quasiperiodic configurations of icosahedral clusters.The models for F-type quasicrystals of Al-Cu-Ru and Al-Pd-Mn system were made, in which the two kinds of icosahedral clusters are arranged quasiperiodically and the clusters are distributed to the two kinds of quasilattice points according to the parity of the indices.The models reproduced well the diffraction profiles, pair distribution functions and the values of other parameters experimentally obtained, which indicates the framework of the models reflects the real structures of the F-type quasicrystals. Less