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

Authors:
  • JGJ.Q. Guo
    J.Q. Guo
  • EAE. Abe
    E. Abe
  • ATA.P. Tsai
    A.P. Tsai
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Abstract
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: 25-85at.%Cd, 0-60at.%Mg and 10-20at.%Yb for the Cd-Mg-Yb system; 33-85at.%Cd, 0-52at.%Mg and 10-20at.%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- 0.5799nm for the Cd-Mg-Yb system and 0.5697-0.5778nm 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.