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 The ternary Laves phases Sc 0.22(1) Ta 0.78(1) Fe 2 and Sc 0.63(1) In 0.37(1) Co 2 were synthesized by arc‐melting appropriate amounts of the binary phases ScFe 2 and TaFe 2 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: P 6 3 / mmc , a =484.96(7), c =793.17(11) pm, wR 2=0.0604, 147 F 2 values, 12 variables for Sc 0.22(1) Ta 0.78(1) Fe 2 and P 6 3 mc , a =488.61(4), c =1599.54(12) pm, wR 2=0.0389, 553 F 2 values, 35 variables for Sc 0.63(1) In 0.37(1) Co 2 . Sc 0.22(1) Ta 0.78(1) Fe 2 derives from the MgZn 2 type having a mixed Sc/Ta occupancy on the 4 f magnesium position. Sc 0.63(1) In 0.37(1) Co 2 crystallizes with a new structure type which derives from the Laves phase MgNi 2 . A translationengleiche symmetry reduction leads to the non‐centrosymmetric space group P 6 3 mc which allows partial Sc/In ordering with different Sc/In ratios on four crystallographically independent sites. While ScFe 2 and TaFe 2 build a complete solid solution Sc 1–x Ta x Fe 2 with MgZn 2 type structure, we observe a switch in structure type for Sc 1–x In x Co 2 from the cubic MgCu 2 type (x=0–0.22) to the non‐centrosymmetric derivative from MgNi 2 at x=0.37.