The systems Sr–Zn–{Si,Ge}: Phase equilibria and crystal structure of ternary phases

Abstract

Phase relations have been established by electron probe microanalysis (EPMA) and X-ray powder diffraction (XPD) for the Sr-poor part of the ternary systems Sr–Zn–Si at 800°C and Sr–Zn–Ge at 700°C. In the Sr–Zn–Si system one new ternary compound SrZn2+xSi2−x (0≤x≤0.45) with CeAl2Ga2 structure and a statistical mixture of Zn/Si in the 4e site was found. Neither a type-I nor a type-IX clathrate phase was encountered. This system is characterized by formation of two further phases, i.e. SrZn1−xSi1+x with ZrBeSi-type (0.16≤x≤0.22) and SrZn1−xSi1+x with AlB2-type (0.35≤x≤0.65) with a random distribution of Zn/Si atoms in the 2c site. For the Sr–Zn–Ge system, the homogeneity regions of the isotypic phases SrZn1−xGe1+x with ZrBeSi-type (0≤x≤0.17) and AlB2-type (0.32≤x≤0.56), respectively, have been determined. Whereas the germanide SrZn2+xGe2−x (CeAl2Ga2-type) is characterized by a homogeneity region (0≤x≤0.5), the clathrate type-I phase Sr8Zn8Ge38 shows a point composition.