Formation of Icosahedral Quasicrystals and 1/1 Crystal Approximants in Al-Pd-RE (RE: Rare Earth Metals) Systems

Abstract

We have investigated the formation of an icosahedral quasicrystal (i-phase) and its 1/1-crystal approximant (1/1-phase) in the (Al, Ga)-Pd-RE (Rare earth metals) systems. Consequently, the Ga-Pd-Sc 1/1-phase, the Al-Pd-RE (RE = Yb, Tm and Er) 1/1-phase and the Al-Pd-Yb i-phase have been newly found by the substitution of Al for Ga, or Sc for other RE in the constituent elements of the Al₅₄Pd₃₀Sc₁₆ i-phase previously reported. For the i- and the 1/1-phases studied in this work, the number of valence electrons per atom (e⁄a) ratio is 2.10 and the atomic radius ratio of the rare earth element to that of the other base elements is in the range 1.15–1.24, which fulfilled the formation conditions previously reported for other Tsai-type i-phases. On the other hand, the stability of the i-phases becomes lower with increasing the atomic radii of the RE elements, which indicates that the atomic radius ratio plays important role in the formation of the Al-Pd-RE i- and 1/1-phases.