Phase Equilibria and Crystal Structures in the Ytterbium–Copper–Zinc system

Phase equilibria in the isothermal section (600 oC) of the ytterbium-copper-zinc ternary system were determined over the entire concentration range by powder X-ray diffraction and scanning electron microscopy with energy-dispersive X-ray spectroscopy. Extended substitutional Cu/Zn homogeneity regions are mainly formed from the Yb-Zn and Yb-Cu binary compounds. There are four ternary compounds, namely τ1-YbCu5-xZnx (cubic AuBe5 type, 0.7 < x ≤ 1.5), τ2-YbCu5-xZnx (hexagonal CaCu5 type, 1.8 ≤ x ≤ 4.4), τ3-Yb2CuZn7 and τ4-Yb5Cu2-xZn1+x. Magnetic measurements were performed for compositions along the phases τ1-YbCu5-xZnx and τ2-YbCu5-xZnx, as well as for the compound Yb33Cu50Zn17 belonging to the pseudobinary system YbCu2-YbZn2. While the Yb ion has a valence of 2+ for compositions ≥33% at % Yb, the Yb valence along the YbCu5-xZnx composition line is influenced by the crystal structure: Yb3+ for the cubic AuBe5 type and nonmagnetic Yb2+ for the hexagonal CaCu5 type.