, M. Nakayama

A P-type icosahedral quasicrystal with a six-dimensional lattice parameter a6D = 7.411 Å is formed as an equilibrium phase in AuAlTm alloy, of which composition was analyzed to be Au46Al38Tm16 by electron probe microanalysis. This quasicrystal is observed as a predominant phase in both as-cast and Au49Al34Tm17 alloys annealed at 910 C, and as one of main phases in the alloy slowly cooled from 1020 C. A 1/1 approximant, Au48Al38Tm14, is also formed near the composition of the quasicrystal. This is a body-centered cubic structure (space group: Im3) with a lattice parameter a = 14.458 Å that is an isostructure to the recently reported 1/1 Tsai-type approximant in AuAlYb. This approximant is characterized by disorderly arranged four AuAl atoms centered at the Tsai-type cluster, presence of atoms at 8c site, and chemical ordering of Au and Al at sites forming a partial triacontahedron