K. Robinson

Bio: K. Robinson is an academic researcher. The author has contributed to research in topics: Crystal structure. The author has an hindex of 1, co-authored 1 publications receiving 284 citations.

Quasicrystal structure of (Al, Zn)49Mg32

Abstract: We express the cubic (Al, Zn)49Mg32 structure as a periodic packing of the rhombohedra1 cells from the three-dimensional Penrose tiling, decorated by atoms. This decoration is extended to the aperiodic quasicrystal packing of the same cells to give a hypothetical structure for the recently discovered icosahedral phase with the same composition. This is the first structure of a real system which is related both to quasicrystals and to Frank-Kasper icosahedral close packings.

A quasicrystal structure model for AI-Mn

Abstract: A model is proposed for the atomic structure of the Al-Mn quasicrystal. Mn icosahedra are connected through their threefold axes, with a coordination number of seven and each bond defined by an octahedron. This Mn skeleton has icosahedral symmetry and its projections onto various planes have a self-similarity property based on the golden number, in agreement with TEM results. The filling up with A1 atoms determines a sublattice where empty Al icosahedra are connected by chains of three distorted octahedra. Two kinds of Mn-Al first-neighbour environments are distinguished, involving nine and ten Al atoms. Taking the ratio of the two Mn site numbers as equal to the golden number leads to a chemical composition in agreement with X-EDS analysis.

Electronic properties of quasicrystals an experimental review

Abstract: The electronic properties of a large number of icosahedral-crystal systems have been studied experimentally. These systems include alloys of the simple metals and those that contain transition metals. Some of the icosahedral phases (i-phases) are thermally stable while others are metastable; and their degree of structural order varies within each of the stability classes. The importance of sample quality to the exposition of intrinsic properties is emphasized, particularly for systems with high resistivities. As a result, experiments on single-phase samples from the diversity of systems studied have shed light on the physics of quasicrystalline alloys. Comparison made with the approximant and amorphous phases have provided important insights to the understanding of quasicrystallinity, randomness, and atomic-potential effects on electronic properties. Reduction in the electronic density of states (DOS) at the Fermi level relative to the free-electronic value is observed in the stable i-phase syste...

Neutron and X-ray single-crystal study of the AlPdMn icosahedral phase

Abstract: Perfect single grains of the AlPdMn icosahedral phase have been used for structure determination by X-ray and neutron diffraction. Owing to the large difference between X-ray and neutron scattering factors, information is gained on the atomic positions of the three elements. A model is proposed as deduced from a six-dimensional (6D) Patterson analysis. Six different atomic hypersurfaces are located on node and body-centre sites of the 6D lattice. The superstructure that leads to a face-centred lattice is mainly due to a strong chemical ordering, all the palladium being on the even node and odd body centre of the 6D cube. The resulting 3D structure contains icosahedral clusters similar to the external shell of the Mackay icosahedron, with two kinds of chemical decoration. The structure may also be described via a quasi-periodic stacking of fivefold planes. Each set of planes is characterized by an average chemical composition and local order. This kind of description helps in the understanding of quasi-crystal growth, formation of dislocations and dynamic properties.