Ternary Laves phases Sc0.22(1)Ta0.78(1)Fe2 and Sc0.63(1)In0.37(1)Co2 – coloring variants of the MgZn2 and MgNi2 type

Abstract

AbstractThe ternary Laves phases Sc0.22(1)Ta0.78(1)Fe2 and Sc0.63(1)In0.37(1)Co2 were synthesized by arc‐melting appropriate amounts of the binary phases ScFe2 and TaFe2 or Sc, In and Co, respectively. The samples were studied by powder X‐ray diffraction and the structures were refined from single crystal X‐ray diffraction data: P63/mmc, a=484.96(7), c=793.17(11) pm, wR2=0.0604, 147 F2 values, 12 variables for Sc0.22(1)Ta0.78(1)Fe2 and P63mc, a=488.61(4), c=1599.54(12) pm, wR2=0.0389, 553 F2 values, 35 variables for Sc0.63(1)In0.37(1)Co2. Sc0.22(1)Ta0.78(1)Fe2 derives from the MgZn2 type having a mixed Sc/Ta occupancy on the 4 f magnesium position. Sc0.63(1)In0.37(1)Co2 crystallizes with a new structure type which derives from the Laves phase MgNi2. A translationengleiche symmetry reduction leads to the non‐centrosymmetric space group P63mc which allows partial Sc/In ordering with different Sc/In ratios on four crystallographically independent sites. While ScFe2 and TaFe2 build a complete solid solution Sc1–xTaxFe2 with MgZn2 type structure, we observe a switch in structure type for Sc1–xInxCo2 from the cubic MgCu2 type (x=0–0.22) to the non‐centrosymmetric derivative from MgNi2 at x=0.37.