Phase relations and crystal structures in the system Ce–Ni–Zn at 800 °C

Abstract

Phase relations have been established for the system Ce–Ni–Zn in the isothermal section at 800°C using electron microprobe analysis and X-ray powder diffraction. Phase equilibria at 800°C are characterized by a large region for the liquid phase covering most of the Ce-rich part of the diagram, whereas a Zn-rich liquid is confined to a small region near the Zn-corner of the Gibbs triangle. Whereas solubility of Ce in the binary Ni-Zn phases is negligible, mutual solubilities of Ni and Zn at a constant Ce content are large at 800°C for most Ce–Zn and Ce–Ni compounds. The solid solution Ce(Ni1−xZnx)5 with the CaCu5-type is continuous throughout the entire section and for the full temperature region from 400 to 800°C. Substitution of Zn by Ni is found to stabilize the structure of CeZn11 to higher temperatures. At 800°C Ce(NixZn1−x)11 (0.03≤x≤0.22) appears as a ternary solution phase. Similarly, a rather extended solution forms for Ce2(NixZn1−x)17 (0≤x≤0.53). Detailed data on atom site occupation and atom parameters were derived from X-ray structure analyses for single crystals of Ce2+y(NixZn1−x)17, y=0.02, x=0.49 (a=0.87541(3), c=1.25410(4)nm; Th2Zn17 type with space group R3¯m,RF2=0.018) and Ce(Ni0.18Zn0.82)11 (a=1.04302(2), c=0.67624(3)nm, BaCd11 type with space group I41/amd, RF2=0.049).