Electronic structures of Cd-based quasicrystals and approximants

摘要

Electronic structures of cubic Cd_6M (M = Yb, Mg and Y), which are approximant crystals of newly discovered Cd-based quasicrystals, are studied theoretically. It is found that stabilization due to alloying is obtained if M is an element with low-lying unoccupied d states. This leads to the conclusion that the cohesion of the Cd-based compounds is certainly de to the hybridization of the d states with a wide sp band. Cd_6M is composed of clusters of icosahedral shape, as are most approximant crystals, but a core of the cluster is of non-icosahedral symmetry. It is found that the atoms in the non-icosahedral core are rather weakly bound and do not play an important role in stabilizing the cluster and its packing. Stability of Zn_(17)Sc_3, which has a similar structure to Cd_6M but has no non-icosahedral core, is understood in the same context as Cd_6M.