DOE OSTI2020
SrMg6Ce crystallizes in the orthorhombic Amm2 space group. The structure is three-dimensional. Sr is bonded to ten Mg and two equivalent Ce atoms to form SrCe2Mg10 cuboctahedra that share corners with four equivalent MgSr2Mg10 cuboctahedra, corners with six equivalent SrCe2Mg10 cuboctahedra, edges with two equivalent MgSr2Mg10 cuboctahedra, edges with four equivalent CeSr2Mg10 cuboctahedra, faces with two equivalent SrCe2Mg10 cuboctahedra, faces with two equivalent CeSr2Mg10 cuboctahedra, and faces with eight MgCe2Mg10 cuboctahedra. There are a spread of Sr–Mg bond distances ranging from 3.35–3.54 Å. Both Sr–Ce bond lengths are 3.53 Å. There are four inequivalent Mg sites. In the first Mg site, Mg is bonded in a 11-coordinate geometry to two equivalent Sr, seven Mg, and two equivalent Ce atoms. There are a spread of Mg–Mg bond distances ranging from 3.34–3.44 Å. There are one shorter (3.24 Å) and one longer (3.57 Å) Mg–Ce bond lengths. In the second Mg site, Mg is bonded to ten Mg and two equivalent Ce atoms to form MgCe2Mg10 cuboctahedra that share corners with four equivalent CeSr2Mg10 cuboctahedra, corners with six equivalent MgCe2Mg10 cuboctahedra, edges with two equivalent CeSr2Mg10 cuboctahedra, edges with four equivalent MgSr2Mg10 cuboctahedra, faces with two equivalent CeSr2Mg10 cuboctahedra, faces with four MgCe2Mg10 cuboctahedra, and faces with six equivalent SrCe2Mg10 cuboctahedra. There are four shorter (3.36 Å) and two longer (3.43 Å) Mg–Mg bond lengths. Both Mg–Ce bond lengths are 3.54 Å. In the third Mg site, Mg is bonded in a 12-coordinate geometry to two equivalent Sr, six Mg, and two equivalent Ce atoms. There are one shorter (3.39 Å) and one longer (3.43 Å) Mg–Mg bond lengths. Both Mg–Ce bond lengths are 3.31 Å. In the fourth Mg site, Mg is bonded to two equivalent Sr and ten Mg atoms to form MgSr2Mg10 cuboctahedra that share corners with four equivalent SrCe2Mg10 cuboctahedra, corners with six equivalent MgSr2Mg10 cuboctahedra, edges with two equivalent SrCe2Mg10 cuboctahedra, edges with four equivalent MgCe2Mg10 cuboctahedra, faces with two equivalent SrCe2Mg10 cuboctahedra, faces with four MgCe2Mg10 cuboctahedra, and faces with six equivalent CeSr2Mg10 cuboctahedra. Ce is bonded to two equivalent Sr and ten Mg atoms to form CeSr2Mg10 cuboctahedra that share corners with four equivalent MgCe2Mg10 cuboctahedra, corners with six equivalent CeSr2Mg10 cuboctahedra, edges with two equivalent MgCe2Mg10 cuboctahedra, edges with four equivalent SrCe2Mg10 cuboctahedra, faces with two equivalent SrCe2Mg10 cuboctahedra, faces with two equivalent CeSr2Mg10 cuboctahedra, and faces with eight MgCe2Mg10 cuboctahedra.