DOE OSTI2020
Mg3Pm 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 Pm atoms to form distorted MgPm4Mg8 cuboctahedra that share corners with four equivalent PmMg12 cuboctahedra, corners with fourteen MgPm4Mg8 cuboctahedra, edges with six equivalent PmMg12 cuboctahedra, edges with twelve MgPm4Mg8 cuboctahedra, faces with four equivalent PmMg12 cuboctahedra, and faces with sixteen MgPm4Mg8 cuboctahedra. There are a spread of Mg–Mg bond distances ranging from 3.23–3.48 Å. There are two shorter (3.29 Å) and two longer (3.39 Å) Mg–Pm bond lengths. In the second Mg site, Mg is bonded to eight Mg and four equivalent Pm atoms to form distorted MgPm4Mg8 cuboctahedra that share corners with four equivalent PmMg12 cuboctahedra, corners with fourteen MgPm4Mg8 cuboctahedra, edges with six equivalent PmMg12 cuboctahedra, edges with twelve MgPm4Mg8 cuboctahedra, faces with four equivalent PmMg12 cuboctahedra, and faces with sixteen MgPm4Mg8 cuboctahedra. There are a spread of Mg–Mg bond distances ranging from 3.23–3.48 Å. There are two shorter (3.29 Å) and two longer (3.39 Å) Mg–Pm bond lengths. In the third Mg site, Mg is bonded to eight Mg and four equivalent Pm atoms to form distorted MgPm4Mg8 cuboctahedra that share corners with four equivalent PmMg12 cuboctahedra, corners with fourteen MgPm4Mg8 cuboctahedra, edges with six equivalent PmMg12 cuboctahedra, edges with twelve MgPm4Mg8 cuboctahedra, faces with four equivalent PmMg12 cuboctahedra, and faces with sixteen MgPm4Mg8 cuboctahedra. Both Mg–Mg bond lengths are 3.23 Å. There are two shorter (3.29 Å) and two longer (3.39 Å) Mg–Pm bond lengths. Pm is bonded to twelve Mg atoms to form PmMg12 cuboctahedra that share corners with six equivalent PmMg12 cuboctahedra, corners with twelve MgPm4Mg8 cuboctahedra, edges with eighteen MgPm4Mg8 cuboctahedra, faces with eight equivalent PmMg12 cuboctahedra, and faces with twelve MgPm4Mg8 cuboctahedra.