DOE OSTI2020
Mg3Tm is beta Cu3Ti-like structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. there are two inequivalent Mg sites. In the first Mg site, Mg is bonded to eight Mg and four equivalent Tm atoms to form MgTm4Mg8 cuboctahedra that share corners with four equivalent TmMg12 cuboctahedra, corners with fourteen MgTm4Mg8 cuboctahedra, edges with six equivalent TmMg12 cuboctahedra, edges with twelve MgTm4Mg8 cuboctahedra, faces with four equivalent TmMg12 cuboctahedra, and faces with sixteen MgTm4Mg8 cuboctahedra. There are a spread of Mg–Mg bond distances ranging from 3.20–3.37 Å. There are two shorter (3.24 Å) and two longer (3.31 Å) Mg–Tm bond lengths. In the second Mg site, Mg is bonded to eight equivalent Mg and four equivalent Tm atoms to form MgTm4Mg8 cuboctahedra that share corners with four equivalent TmMg12 cuboctahedra, corners with fourteen MgTm4Mg8 cuboctahedra, edges with six equivalent TmMg12 cuboctahedra, edges with twelve equivalent MgTm4Mg8 cuboctahedra, faces with four equivalent TmMg12 cuboctahedra, and faces with sixteen MgTm4Mg8 cuboctahedra. There are two shorter (3.24 Å) and two longer (3.31 Å) Mg–Tm bond lengths. Tm is bonded to twelve Mg atoms to form TmMg12 cuboctahedra that share corners with six equivalent TmMg12 cuboctahedra, corners with twelve MgTm4Mg8 cuboctahedra, edges with eighteen MgTm4Mg8 cuboctahedra, faces with eight equivalent TmMg12 cuboctahedra, and faces with twelve MgTm4Mg8 cuboctahedra.