A P-type icosahedral quasicrystal is formed in Au-Al-Yb alloy of which 6-dimensional lattice parameter a 6D = 7.448 Å. The composition of the quasicrystal was analyzed to be Au 51 Al 34 Yb 15 . This quasicrystal is formed in as-cast alloys, and is regarded as metastable because of decomposition into other crystalline phases by annealing at 700 ºC. Among Tsai-type quasicrystals, this quasicrystal is situated just between Zn-Sc group with smaller a 6D and larger Cd-Yb group. Intermediate valence of Yb recently observed in this quasicrystal may be due to this unique situation, namely smaller major component Au-Al than in Cd-Yb.The predominant phase in the annealed specimen is a 1/1 cubic approximant with lattice parameter a = 14.500 Å belonging to the space group Im ! 3. This phase is stable at the composition Au 51 Al 35 Yb 14 at 700 ºC. Rietveld structural analysis indicated that the crystal structure is understood as periodic arrangement of Tsai-type clusters each

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Starting from the Zn 17 Sc 3 cubic approximant, new quasicrystal alloys were searched by replacement of Zn with transition elements, T. In the cases of T=Mn, Fe, Co and Ni, new icosahedral quasicrystals are formed in as-cast alloys as major phases at the alloy compositions of Zn 75 T 10 Sc 15 . All these quasicrystals belong to a primitive type, and have 6-dimensional lattice parameters, a 6D , ranging from 7.044 to 7.107 Å. They have the valence electron concentrations, e/a, ranging from 2.01 to 2.14, and almost the same ratios between the edge-length of the Penrose tile, a R , and the averaged atomic diameter d: a R /d~1.75. Moreover other Zn-and Cd-based quasicrystals including the same type of atomic cluster, Tsai-type cluster, also have the same values of e/a~2.1 and a R /d~1.75. The equality in e/a indicates that the Hume-Rothery mechanism plays an important role for the formation of these quasicrystals.

Quantum criticality has been considered to be specific to crystalline materials such as heavy Tsai-type quasicrystal and that both possess no localized magnetic moment. We suggest that the Au-Al-Yb system is located near the border of the divalent and trivalent states of the Yb ion; we also discuss a possible origin of the disappearance of magnetism, associated with the valence change, by the substitution of the constituent elements.