ICOSAHEDRAL ALLOYS GROWN IN AL EXCESS - PROBLEMS OF DISORDER AND STABILITY

Phonon- and random-phason-type structural disorder was measured in Al- transition metal (Tm) ternary alloys, prepared with Al excess by rapid quenching. The disorder parameters correlate with the calculations on the energy stability of Al12TM icosahedra. Thus, substitution of 'uns table' elements (Fe and Co) for 'stable' elements (Cr and Mn) causes a strong increase in both types of disorder, leading finally to crystal lization. This chemical trend is modulated around special compositions of the TM sublattice. The degree of structural order correlates with the thermal stability of icosahedral phases.