Peritectic Formation and Phase Stability of the Icosahedral Quasicystal i‑GdCd and Its Ternary Variants with Zn, Mg, and Y

Stable binary icosahedral quasicrystals (i-QCs) based on rare earth (RE) and cadmium are typically accessed by solution growth experiments, which operate in very narrow composition and temperature windows. Here, we present a procedure which allows study of peritectic reactions between approximant crystal (AC) phase and liquid yielding i-RECd and exemplify with i-GdCd and ternary variants where Cd is partially replaced by isovalent Zn (i-Gd­(Cd,Zn)) or Mg (i-Gd­(Cd,Mg)), or the 4f element Gd is replaced by nonmagnetic Y (i-(Gd,Y)­Cd). The solubility limits for Zn and Mg substitution are about 10% and 20%, respectively, whereas Gd and Y show a complete solid solution behavior. We find that the peritectic decomposition temperature for i-GdCd is 390 °C, which is decreased when Gd is replaced by Y (i-YCd: 350 °C) and increased when Cd is replaced by Zn (i-Gd­(Cd₉₀Zn₁₀): 440 °C), and especially by Mg (i-Gd­(Cd₈₀Mg₂₀): 520 °C). Whereas substitution decisively alters the decomposition temperature (and hence stability) of the considered i-QCs, the decomposition temperature of the corresponding AC phases remains at around 700 °C. During the investigation of the pseudobinary phase diagrams Gd-(Cd₉₅Zn₅), Gd-(Cd₉₀Zn₁₀), and Gd-(Cd₈₀Mg₂₀), faceted i-QCs grains with sizes up to 4 × 4 × 4 mm³ could be isolated.