DOE OSTI2020
MgCo3 is beta Cu3Ti-like structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Mg is bonded to twelve Co atoms to form MgCo12 cuboctahedra that share corners with six equivalent MgCo12 cuboctahedra, corners with twelve equivalent CoMg4Co8 cuboctahedra, edges with eighteen CoMg4Co8 cuboctahedra, faces with eight equivalent MgCo12 cuboctahedra, and faces with twelve CoMg4Co8 cuboctahedra. There are six shorter (2.61 Å) and six longer (2.62 Å) Mg–Co bond lengths. There are two inequivalent Co sites. In the first Co site, Co is bonded to four equivalent Mg and eight Co atoms to form distorted CoMg4Co8 cuboctahedra that share corners with four equivalent MgCo12 cuboctahedra, corners with fourteen equivalent CoMg4Co8 cuboctahedra, edges with six equivalent MgCo12 cuboctahedra, edges with twelve CoMg4Co8 cuboctahedra, faces with four equivalent MgCo12 cuboctahedra, and faces with sixteen CoMg4Co8 cuboctahedra. There are a spread of Co–Co bond distances ranging from 2.49–2.72 Å. In the second Co site, Co is bonded to four equivalent Mg and eight equivalent Co atoms to form distorted CoMg4Co8 cuboctahedra that share corners with four equivalent MgCo12 cuboctahedra, corners with fourteen CoMg4Co8 cuboctahedra, edges with six equivalent MgCo12 cuboctahedra, edges with twelve equivalent CoMg4Co8 cuboctahedra, faces with four equivalent MgCo12 cuboctahedra, and faces with sixteen CoMg4Co8 cuboctahedra.