Geometric structure of Bergman clusters related to bulk amorphous alloys and quasicrystals

Abstract

The fcc Zr₂Ni- and MgCu₂-type phases, being primary crystalline products of certain amorphous alloys with high glass-forming ability, should provide local structural information about the related amorphous alloys. The present paper gives a detailed analysis of the common structural features of these two fcc phases. They are both built from a similar building block consisting of tetrahedrally packed icosahedra. They also have shelled local structures similar to the first two shells of the Bergman-type clusters found in many icosahedral quasicrystals. Therefore the Bergman-type clusters probably play an important role in amorphous phase formation. Because of topological close packing inside dual-intergrown icosahedra, characteristic of Bergman clusters, the atomic radius ratios of the first- and second-shell atoms with respect to the central atom are nearly equal and fall in the range 1.1–1.2.

Acknowledgements

This work was supported by the key foundation and key teacher foundation from the Education Ministry of China and by the Natural Science Foundation of China under grant 50271012. One of us (P. T.) acknowledges support from the Director, Office of Science, Basic Energy Sciences, Materials Science Division of the US Department of Energy under contract W-405-Eng-82.