Stable Cd-Mg-Yb and Cd-Mg-Ca icosahedral quasicrystals with wide composition ranges

Stable icosahedral quasicrystals with wide composition ranges have been found in the systems Cd-Mg-Yb and Cd-Mg-Ca. The icosahedral quasicrystals form in the following composition ranges: 25-85 at.% Cd, 0-60 at.% Mg and 10-20 at.% Yb for the Cd-Mg-Yb system; 33-85 at.% Cd, 0-52 at.% Mg and 10-20 at.% Ca for the Cd-Mg-Ca system. An electron diffraction study confirmed that the icosahedral quasicrystals have a primitive lattice. Its quasilattice constant is proportional to a Goldschmidt atom diameter of the quasicrystals weighted by a factor of 1.75 in the range 0.5681- 0.5799 nm for the Cd-Mg-Yb system and 0.5697-0.5778 nm for the Cd-Mg-Ca system. The closely similar atom sizes of Cd and Mg, the valence electron ratio e/a=2.0 and the large atom sizes of Yb and Ca cause the wide composition ranges of the Cd-Mg-Yb and Cd-Mg-Ca quasicrystals. The metallurgical behaviour of the quasicrystals is discussed.