Hybridization mechanism for cohesion of Cd-based quasicrystals.

The cohesion mechanism of cubic approximant crystals in newly discovered binary quasicrystals, Cd(6)M ( M = Yb or Ca), is 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 Cd-based compounds is due to hybridization of the d states of Yb and Ca with a wide sp band. The Hume-Rothery mechanism does not play a principal role in the stability because neither a distinct pseudogap nor stabilization due to alloying is obtained for isostructural Cd-Mg. In addition to the electronic origin, matching of the atomic size is very crucial for quasicrystal formation in Cd-based compounds.