Abstract
A thermodynamically stable quasi-crystalline single phase with an icosahedral structure was found to be formed at atomic compositions of Al65Cu20Ru15 and Al65Cu20Os15 in conventionally solidified and fully annealed states as well as in a rapidly solidified state. The quasi-crystalline nature determined by X-ray diffractometry is the highest for the fully annealed ingot, indicating the existence of a truly equilibrium icosahedral structure. The stable quasi-crystals appear to have a growth morphology of pentagonal dodecahedron with an average size of 0.03 mm in a fully annealed state.