Abstract
Recent progress on a new group of icosahedral quasicrystals is reviewed. This group is characterized by Tsai-type atomic cluster as a local structural unit, which is different from Mackay and Bergman-types. This group can be regarded as largest including two Cd-based binary, seven Zn-based and ten Cd-based ternary stable phases as well as Cu- and Ag-based phases. They are all P-type, and some of them exhibit higher degree of structural perfection than the “perfect” Al-Pd-Mn quasicrystal. In the Tsai-type quasicrystals, there are substitution rules in the constituent elements. Hume-Rothery rules, namely the equality in e/a and in the ratio of atomic radii, play important role in the substitution rules.
