The γ-brass structure and the Boerdijk-Coxeter helix

Lord, E. A. ; Ranganathan, S. (2004) The γ-brass structure and the Boerdijk-Coxeter helix Journal of Non-Crystalline Solids, 334-335 . pp. 121-125. ISSN 0022-3093

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The γ -brass structure was for a long time regarded as a modified bcc structure. It is more accurately described in terms of a 26-atom cluster consisting of four interpenetrating icosahedral clusters. An alternative description in terms of a 38-atom cluster is also illuminating. We discuss the γ -brass structure in terms of the packing of spheres and the packing of 'almost regular' tetrahedra and demonstrate a close relationship to the helical sphere packings investigated by Boerdijk, who considered the configuration of touching spheres centred at the vertices of a Coxeter helix, and extended it by adding an extra layer of spheres. Adding a further layer of spheres gives a rod-like structure in which every sphere of the original helix is surrounded by twelve others, configured as a somewhat distorted icosahedron. Thus each tetrahedron of the initial structure is then shared by four icosahedra. This 26-sphere cluster is a slightly distorted form of the 26-atom γ -brass cluster.

Item Type:Article
Source:Copyright of this article belongs to Elsevier Science.
ID Code:42084
Deposited On:01 Jun 2011 14:40
Last Modified:01 Jun 2011 14:40

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