The system Ba–Zn–Sn at 500 °C: Phase equilibria, crystal and electronic structure of ternary phases

• Phase relations for the Ba-poor part of the Ba–Zn–Sn system established at 500 °C.
• New ternary compound BaZnSn2 crystallizes in CeNiSi2 structure type.
• A homogeneity region has been defined for the BaZn1−xSn1+x (0.22 ⩽ x ⩽ 0.35) compound.
• BaZn2Sn2 is characterized by mixed Zn/Sn occupancy and a small amount of vacancies.
• The solubility of Sn in the Ba8Zn7Si39 clathrate was found to be <1 at.%.

Phase relations for the Ba-poor part of the ternary system Ba–Zn–Sn at 500 °C were established by electron probe microanalysis (EPMA) and X-ray powder diffraction (XPD). Besides the already known compounds BaZnSn (ZrBeSi type) and BaZn2Sn2 (CaBe2Ge2 type), a novel ternary compound BaZnSn2 was found to crystallize with the CeNiSi2-type. The precise determination (EPMA) of the homogeneity region at 500 °C for the compound BaZn1−xSn1+x with the ZrBeSi type (0.22 ⩽ x ⩽ 0.35) excludes the stoichiometric composition. The stannide BaZn2−xSn2+x (x = 0.05) is characterized by mixed occupancy of Zn and Sn atoms in the 2c site; accordingly the composition is slightly shifted from stoichiometry 1:2:2. Structural effects in the Ba–Zn–Sn compounds were explained on the basis of crystal chemistry analyses and electronic structure calculations employing the electron localization function ELF. The solubility of Sn in the clathrate phase Ba8Zn7Si39 was found to be insignificant (around 1 at.%; 800 °C).

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