Icosahedral quasicrystal, 1/1 and 2/1 approximants in Zn-based ternary alloys containing Au and Yb/Tb

TL;DR

This study reports the formation of Tsai-type icosahedral quasicrystals and their approximants in Zn-based ternary alloys containing Au and Yb/Tb, revealing new phases and substitution possibilities in related systems.

Contribution

It identifies new quasicrystal and approximant phases in Zn-Au-Yb/Tb alloys and demonstrates their relation to binary Cd-lanthanoid systems.

Findings

Quasicrystal forms in quenched alloys at specific compositions.

Stable 2/1 approximant forms in annealed alloys.

New phases suggest isostructural substitution possibilities.

Abstract

In a narrow composition range centered at Zn74.5Au10.5Yb15.0, Tsai-type icosahedral quasicrystal is formed in alloys quenched from 880 C. This quasicrystal belongs to the primitive type with the 6-dimensional lattice parameter a6D=7.378 A. The quasicrystal was not formed in the slowly cooled specimen, and was considered a metastable phase. The stable phase is a 2/1 approximant of the lattice parameter a2/1=23.271 A. This approximant forms exclusively in Zn76.0Au9.0Yb15.0 alloy annealed at 530 C. In addition, Zn70.5Au15.5Tb14.0 alloy annealed at 505 C forms a Tsai-type 1/1 approximant (a1/1=14.343 A). These new Zn-based phases observed in this study correspond to the quasicrystal-related phases in binary Cd-lanthanoid systems, and show the possibility of isostructural substitution of Cd by Zn/Au.