DOE OSTI2020
Mg3Pa 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 Pa atoms to form distorted MgMg8Pa4 cuboctahedra that share corners with four equivalent PaMg12 cuboctahedra, corners with fourteen MgMg8Pa4 cuboctahedra, edges with six equivalent PaMg12 cuboctahedra, edges with twelve MgMg8Pa4 cuboctahedra, faces with four equivalent PaMg12 cuboctahedra, and faces with sixteen MgMg8Pa4 cuboctahedra. There are a spread of Mg–Mg bond distances ranging from 3.19–3.37 Å. There are two shorter (3.23 Å) and two longer (3.31 Å) Mg–Pa bond lengths. In the second Mg site, Mg is bonded to eight equivalent Mg and four equivalent Pa atoms to form distorted MgMg8Pa4 cuboctahedra that share corners with four equivalent PaMg12 cuboctahedra, corners with fourteen MgMg8Pa4 cuboctahedra, edges with six equivalent PaMg12 cuboctahedra, edges with twelve equivalent MgMg8Pa4 cuboctahedra, faces with four equivalent PaMg12 cuboctahedra, and faces with sixteen MgMg8Pa4 cuboctahedra. There are two shorter (3.23 Å) and two longer (3.31 Å) Mg–Pa bond lengths. Pa is bonded to twelve Mg atoms to form PaMg12 cuboctahedra that share corners with six equivalent PaMg12 cuboctahedra, corners with twelve MgMg8Pa4 cuboctahedra, edges with eighteen MgMg8Pa4 cuboctahedra, faces with eight equivalent PaMg12 cuboctahedra, and faces with twelve MgMg8Pa4 cuboctahedra.