Structural features of intermetallic phases in the Ca-Zn-Al system

The Ca–Zn–Al system has been investigated in the region from 8 to 33 at% Ca. The results show that the following phases are solid solutions based on the corresponding known binary compounds: Ca(Zn1–xAlx)3 (x = 0 – 0.23, CaZn3 type), Ca(Zn1–xAlx)4 (x = 0.47 – 1.00, BaAl4 type), Ca1–y(Zn1–xAlx)5+2y (x = 0 – 0.12 and y = 0 – 0.12, CaCu5-derived TbCu7 type), Ca(Zn1–xAlx)11 (x = 0 – 0.018, BaCd11 type), while the phase Ca2(Zn1–xAlx)17 (x = 0.05 – 0.17, Th2Zn17 type) exists with a ternary composition only. In all pseudobinary systems the cell volume generally increases with increasing Al content, as expected for the higher atomic volume of Al compared with Zn. A substitution of Al for Zn is generally observed, but preferential occupations, namely different Al/Zn ratio values, occur for different crystallographic sites. This phenomenon gives rise to anomalous trends in the variations of the lattice parameters.