Kazumasa Sugiyama

Crystal structure of a cubic Al17Zn37Mg46; a 2/1 rational approximant structure for the Al–Zn–Mg icosahedral phase

Abstract The crystalline structure of a 2/1 cubic approximant phase Al 17 Zn 37 Mg 46 ( Pa 3, a =23.1 A) for the Al–Zn–Mg icosahedral phase has been determined by the single crystal X-ray diffraction. The structure of the present 2/1 approximant is characterized by the packing of Bergman clusters and the atomic arrangements for six successive shells are similar to those found in the 1/1 cubic approximant. However, the fourth rhombicosidodecahedral shell of the 2/1 cubic approximant indicates a rather distorted figure together with the chemical disorder. This reflects the unique packing motif of the Bergman clusters in the 2/1 cubic approximant.

Al13M4-type structures and atomic models of their twins

Abstract From the structural analysis of Al 13 Fe 4 and Al 13 Co 4 phases as well as a new Al 13 (Pd, Fe) 4 phase with single-crystal X-ray diffraction, their structures were examined in terms of tilings of two types of pentagonal columns, which have similar atomic arrangements in the three phases. It has been found that the tilings of the pentagonal columns in these phases are characterized as arrangements of squashed hexagonal tiles formed by an edge-sharing linkage of the pentagonal columns, and that there is a rule for arrangements of the pentagonal columns forming the hexagonal tiles. It has been found from high-resolution electron microscopy observations that the structures of twins in the three phases can be interpreted by this topological rule for arrangements of the pentagonal columns.

Crystal structure of a new 1/1-rational approximant for the Al–Cu–Ru icosahedral phase

Abstract The structure of a cubic Al 57.3 Cu 31.4 Ru 11.3 phase, which is referred to as an 1/1-rational approximant of an Al–Cu–Ru icosahedral phase, was determined by means of a single crystal X-ray structural analysis: space group Pm 3 (No. 200), a =12.3773(8) A, V =1896.2(2) A 3 , MoKα ( λ =0.71073 A); atoms/cell=122.6, F (000)=2645, D calc =5.04 Mg/m 3 , R =0.0495 for the observed 1140 reflections with F obs. >4.0 σ ( F obs. ). Cu- and Ru-rich icosidodecahedral atom clusters are recognized at the 1 a and 1 b sites of the unit cell, respectively. The atom clusters possess Ru centers and the surrounding first shells of about 2.5 A in diameter show heavily disordered features with partial breakdown of the local icosahedral symmetry. These chemically and topologically decorated Mackay-like atom clusters should be classified as the fundamental structural units for the F-type Al–Cu–Ru icosahedral phase.

Crystalline structure of a Cu-substituted λ-Al13Fe4 phase by means of the anomalous X-ray scattering

Abstract The structure of a Cu-substituted λ-Al13Fe4 phase was analyzed by the single crystal X-ray diffraction (XRD) coupled with the anomalous X-ray scattering (AXS) at Cu K absorption edge. The AXS analysis revealed the Cu distribution at Fe/Cu(1), Fe/Cu(2), Fe/Cu(3), Al/Cu(9), Cu(12) and Al/Cu(14) sites and such information was readily applied in order to improve the structural model obtained by the ordinary single crystal X-ray diffraction. Present results clearly demonstrate the usefulness of the AXS technique for the structural analysis of chemically disordered materials.

On the crystal structures of the Al–Cu–Cr alloy system

Abstract The structures of hexagonal ζ-Al 72.6 Cu 11.0 Cr 16.4 ( P 6 3 / m ; a =17.714(3) A, c =12.591(2) A) and face centered cubic β-Al 67.4 Cu 14.3 Cr 18.3 ( F 43 m ; a =18.161(1) A) phases were determined by means of single crystal X-ray structural analysis. The ζ-phase is found at a relatively wide range of chemical composition of Al 80–65 Cu 5–20 Cr 15 and revealed as an iso-structure with κ-AlCrNi. On the other hand, the β-phase indicates the Na 6 Tl-type structure with more Cr-rich chemical composition around Al 65 Cu 17.5 Cr 17.5 . These structures are well featured by the linkage of icosahedra with a heavy metal center.

Model for the microstructure of oxide eutectics and comparison with experimental observations

Abstract The properties of eutectic materials depend strongly on their microstructure. In the case of oxide systems, which exhibit complex microstructures due to the tendencies of the two phases to grow in a faceted manner, conventional eutectic growth theory has been unable to give a detailed account of the process of microstructure formation. We describe here a cellular automata-based model that is able to reproduce key features and general trends observed experimentally in our investigations of oxide eutectic fibers of Al2O3/R3Al5O12, Al2O3/RAlO3, and related systems, where R is one of a series of rare earth elements. The most important parameters controlling the type of microstructure that develops are the volume fractions and faceting tendencies of the two components. The model provides guidelines for the design of materials with optimized microstructures for particular applications.