STRUCTURAL MODELING OF ICOSAHEDRAL AND SIMPLE CUBIC APPROXIMANT PHASEIN AL-MN(FE)-SI SYSTEM

In spite of various models being available for the icosahedral quasicr ystal structure in Al-Mn(Fe)-Si system, a consistent model for describ ing the simple cubic approximant and icosahahedral structure in terms of rational and irrational sections of the same six dimensional cubic crystal seems to be lacking. Such a model is presented and the subtle difference between the present model and the previous ones is discusse d. The necessity of such considerations is spelt out while accomplishi ng the partitioning of the tricontahedral motif (with extension in thr ee dimensional pseudo direct space) based on the chemistry of the allo y. An algorithm for generating the required polyhedra for partitioning is also presented.