DOE OSTI2020
SmMg3 is beta Cu3Ti-like structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. there are three inequivalent Mg sites. In the first Mg site, Mg is bonded to eight Mg and four equivalent Sm atoms to form distorted MgSm4Mg8 cuboctahedra that share corners with four equivalent SmMg12 cuboctahedra, corners with fourteen MgSm4Mg8 cuboctahedra, edges with six equivalent SmMg12 cuboctahedra, edges with twelve MgSm4Mg8 cuboctahedra, faces with four equivalent SmMg12 cuboctahedra, and faces with sixteen MgSm4Mg8 cuboctahedra. There are a spread of Mg–Mg bond distances ranging from 3.22–3.48 Å. There are two shorter (3.29 Å) and two longer (3.39 Å) Mg–Sm bond lengths. In the second Mg site, Mg is bonded to eight equivalent Mg and four equivalent Sm atoms to form distorted MgSm4Mg8 cuboctahedra that share corners with four equivalent SmMg12 cuboctahedra, corners with fourteen MgSm4Mg8 cuboctahedra, edges with six equivalent SmMg12 cuboctahedra, edges with twelve equivalent MgSm4Mg8 cuboctahedra, faces with four equivalent SmMg12 cuboctahedra, and faces with sixteen MgSm4Mg8 cuboctahedra. There are two shorter (3.29 Å) and two longer (3.39 Å) Mg–Sm bond lengths. In the third Mg site, Mg is bonded to eight equivalent Mg and four equivalent Sm atoms to form distorted MgSm4Mg8 cuboctahedra that share corners with four equivalent SmMg12 cuboctahedra, corners with fourteen MgSm4Mg8 cuboctahedra, edges with six equivalent SmMg12 cuboctahedra, edges with twelve equivalent MgSm4Mg8 cuboctahedra, faces with four equivalent SmMg12 cuboctahedra, and faces with sixteen MgSm4Mg8 cuboctahedra. There are two shorter (3.29 Å) and two longer (3.39 Å) Mg–Sm bond lengths. Sm is bonded to twelve Mg atoms to form SmMg12 cuboctahedra that share corners with six equivalent SmMg12 cuboctahedra, corners with twelve MgSm4Mg8 cuboctahedra, edges with eighteen MgSm4Mg8 cuboctahedra, faces with eight equivalent SmMg12 cuboctahedra, and faces with twelve MgSm4Mg8 cuboctahedra.