Ternary magnesium gallides – synthesis, crystal chemistry and properties of CaMgGa, SrMgGa, BaMgGa and YbMgGa

Abstract The gallides CaMgGa, SrMgGa, BaMgGa and YbMgGa were synthesized from the elements in sealed tantalum ampoules in muffle furnaces. The phase purity of the samples was checked by powder X‐ray diffraction. CaMgGa and YbMgGa crystallize with the ZrNiAl type structure, space group P 2 m , whereas SrMgGa and BaMgGa adopt an ordering variant of the Cu 2 Sb/PbFCl type, space group P 4/ nmm . The structures of SrMg 0.884(7) Ga 1.116(7) ( a =459.23(9), c =792.43(12) pm, wR 2=0.0371, 226 F 2 values, 11 variables) and YbMgGa ( a =774.55(7), c =411.95(4) pm, wR 2=0.0329, 342 F 2 values, 15 variables) were refined from single crystal X‐ray diffractometer data. Refinement of the occupancy parameters indicated a small degree of Mg/Ga mixing on the 2 a site for the strontium compound. The [MgGa] substructures in both compounds are composed of condensed Mg@Ga 4 tetrahedra with 4×287 pm Mg−Ga in SrMg 0.884 Ga 1.116 vs 2×282 and 2×296 pm in YbMgGa. The SrMgGa structure has a stacking of layers of edge‐sharing Mg@Ga 4 and Sr 4 tetrahedra. Electronic structure calculations indicate a net charge transfer from strontium and magnesium to gallium. YbMgGa completes the series of RE MgGa gallides. Temperature dependent magnetic susceptibility studies reveal weak Pauli paramagnetism, confirming divalent ytterbium.