Formation condition of the icosahedral phase in rapidly quenched Ag-In-RE (rare earth) alloys

Formation of icosahedral ( i ) phases in rapidly quenched Ag-In-RE (rare earth) (RE = Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb) ternary alloys is investigated. It is found that the relative magnitude of the quasilattice constant is well explained by the atomic radius of the RE elements for Ag-In-RE alloys with trivalent RE elements, and the formation of the i phase is governed by the atomic radius of the RE element. Moreover, the i phase is found to be formed in a wide composition range for the Ag/In atomic ratio but in a very narrow range for the RE concentration, which suggests that the RE concentration plays a crucial role in the formation, i.e. the stability, of the i phase rather than the average electrons-per-atom ratio. Furthermore, it is suggested that the structural change caused by the variation of the Ag/In concentration ratio in the i phase cannot be understood as a consequence of simple mutual replacement between Ag and In.