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

Abstract

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.

Eu Doping in the GdCd7.88 Quasicrystal and Its Approximant Crystal GdCd6

“…(b) Superposition of the pure binary Gd–Cd (red) and Eu–Cd (blue) phase diagrams; the arrows indicate the qualitative changes of the phase diagram as the Eu concentration increases. The phase diagrams in (b) were taken from refs and .…”

2D crystal structure and anisotropic magnetism of GdAu6.75−xAl0.5+x (x ≈ 0.54)

“…It is sometimes possible to apply a pseudo-binary approach (e.g. Gd 14 X 86 ) in which the majority component X is replaced by a binary mixture at or close the eutectic composition 15 . This can provide a situation where the liquidus temperature is below the peritectic temperature of the QC phase and thus allow access to QC phase through crystallization from the melt.…”