ErCe is beta-derived structured and crystallizes in the trigonal R3m space group. There are five inequivalent Er sites. In the first Er site, Er(1) is bonded to three equivalent Er(3), six equivalent Er(1), and three equivalent Ce(2) atoms to form ErCe3Er9 cuboctahedra that share corners with three equivalent Er(2)Ce6Er6 cuboctahedra, corners with six equivalent Er(1)Ce3Er9 cuboctahedra, corners with six equivalent Ce(1)Ce9Er3 cuboctahedra, edges with three equivalent Er(2)Ce6Er6 cuboctahedra, edges with six equivalent Er(1)Ce3Er9 cuboctahedra, edges with six equivalent Er(3)Ce3Er9 cuboctahedra, edges with six equivalent Ce(2)Ce6Er6 cuboctahedra,  a faceface with one Ce(1)Ce9Er3 cuboctahedra, faces with six equivalent Er(1)Ce3Er9 cuboctahedra, faces with six equivalent Er(3)Ce3Er9 cuboctahedra, and faces with six equivalent Ce(2)Ce6Er6 cuboctahedra. In the second Er site, Er(2) is bonded to six equivalent Er(2), three equivalent Ce(2), and three equivalent Ce(3) atoms to form ErCe6Er6 cuboctahedra that share corners with three equivalent Er(1)Ce3Er9 cuboctahedra, corners with six equivalent Er(2)Ce6Er6 cuboctahedra, corners with six equivalent Ce(1)Ce9Er3 cuboctahedra, edges with three equivalent Er(1)Ce3Er9 cuboctahedra, edges with six equivalent Er(2)Ce6Er6 cuboctahedra, edges with six equivalent Ce(2)Ce6Er6 cuboctahedra, edges with six equivalent Ce(3)Ce9Er3 cuboctahedra,  a faceface with one Ce(1)Ce9Er3 cuboctahedra, faces with six equivalent Er(2)Ce6Er6 cuboctahedra, faces with six equivalent Ce(2)Ce6Er6 cuboctahedra, and faces with six equivalent Ce(3)Ce9Er3 cuboctahedra. In the third Er site, Er(3) is bonded to three equivalent Er(1), six equivalent Er(3), and three equivalent Ce(1) atoms to form ErCe3Er9 cuboctahedra that share corners with three equivalent Ce(3)Ce9Er3 cuboctahedra, corners with six equivalent Er(3)Ce3Er9 cuboctahedra, corners with six equivalent Ce(2)Ce6Er6 cuboctahedra, edges with three equivalent Ce(3)Ce9Er3 cuboctahedra, edges with six equivalent Er(1)Ce3Er9 cuboctahedra, edges with six equivalent Er(3)Ce3Er9 cuboctahedra, edges with six equivalent Ce(1)Ce9Er3 cuboctahedra,  a faceface with one Ce(2)Ce6Er6 cuboctahedra, faces with six equivalent Er(1)Ce3Er9 cuboctahedra, faces with six equivalent Er(3)Ce3Er9 cuboctahedra, and faces with six equivalent Ce(1)Ce9Er3 cuboctahedra. In the fourth Er site, Er(2) is bonded to six equivalent Er(2), three equivalent Ce(2), and three equivalent Ce(3) atoms to form ErCe6Er6 cuboctahedra that share corners with three equivalent Er(1)Ce3Er9 cuboctahedra, corners with six equivalent Er(2)Ce6Er6 cuboctahedra, corners with six equivalent Ce(1)Ce9Er3 cuboctahedra, edges with three equivalent Er(1)Ce3Er9 cuboctahedra, edges with six equivalent Er(2)Ce6Er6 cuboctahedra, edges with six equivalent Ce(2)Ce6Er6 cuboctahedra, edges with six equivalent Ce(3)Ce9Er3 cuboctahedra,  a faceface with one Ce(1)Ce9Er3 cuboctahedra, faces with six equivalent Er(2)Ce6Er6 cuboctahedra, faces with six equivalent Ce(2)Ce6Er6 cuboctahedra, and faces with six equivalent Ce(3)Ce9Er3 cuboctahedra. In the fifth Er site, Er(2) is bonded to six equivalent Er(2), three equivalent Ce(2), and three equivalent Ce(3) atoms to form ErCe6Er6 cuboctahedra that share corners with three equivalent Er(1)Ce3Er9 cuboctahedra, corners with six equivalent Er(2)Ce6Er6 cuboctahedra, corners with six equivalent Ce(1)Ce9Er3 cuboctahedra, edges with three equivalent Er(1)Ce3Er9 cuboctahedra, edges with six equivalent Er(2)Ce6Er6 cuboctahedra, edges with six equivalent Ce(2)Ce6Er6 cuboctahedra, edges with six equivalent Ce(3)Ce9Er3 cuboctahedra,  a faceface with one Ce(1)Ce9Er3 cuboctahedra, faces with six equivalent Er(2)Ce6Er6 cuboctahedra, faces with six equivalent Ce(2)Ce6Er6 cuboctahedra, and faces with six equivalent Ce(3)Ce9Er3 cuboctahedra. There are four inequivalent Ce sites. In the first Ce site, Ce(1) is bonded to three equivalent Er(3), three equivalent Ce(3), and six equivalent Ce(1) atoms to form CeCe9Er3 cuboctahedra that share corners with six equivalent Er(1)Ce3Er9 cuboctahedra, corners with six equivalent Er(2)Ce6Er6 cuboctahedra, corners with six equivalent Ce(1)Ce9Er3 cuboctahedra, edges with six equivalent Er(3)Ce3Er9 cuboctahedra, edges with six equivalent Ce(1)Ce9Er3 cuboctahedra, edges with six equivalent Ce(3)Ce9Er3 cuboctahedra,  a faceface with one Er(1)Ce3Er9 cuboctahedra,  a faceface with one Er(2)Ce6Er6 cuboctahedra, faces with six equivalent Er(3)Ce3Er9 cuboctahedra, faces with six equivalent Ce(1)Ce9Er3 cuboctahedra, and faces with six equivalent Ce(3)Ce9Er3 cuboctahedra. In the second Ce site, Ce(2) is bonded to three equivalent Er(1), three equivalent Er(2), and six equivalent Ce(2) atoms to form CeCe6Er6 cuboctahedra that share corners with six equivalent Er(3)Ce3Er9 cuboctahedra, corners with six equivalent Ce(2)Ce6Er6 cuboctahedra, corners with six equivalent Ce(3)Ce9Er3 cuboctahedra, edges with six equivalent Er(1)Ce3Er9 cuboctahedra, edges with six equivalent Er(2)Ce6Er6 cuboctahedra, edges with six equivalent Ce(2)Ce6Er6 cuboctahedra,  a faceface with one Er(3)Ce3Er9 cuboctahedra,  a faceface with one Ce(3)Ce9Er3 cuboctahedra, faces with six equivalent Er(1)Ce3Er9 cuboctahedra, faces with six equivalent Er(2)Ce6Er6 cuboctahedra, and faces with six equivalent Ce(2)Ce6Er6 cuboctahedra. In the third Ce site, Ce(3) is bonded to three equivalent Er(2), three equivalent Ce(1), and six equivalent Ce(3) atoms to form CeCe9Er3 cuboctahedra that share corners with three equivalent Er(3)Ce3Er9 cuboctahedra, corners with six equivalent Ce(2)Ce6Er6 cuboctahedra, corners with six equivalent Ce(3)Ce9Er3 cuboctahedra, edges with three equivalent Er(3)Ce3Er9 cuboctahedra, edges with six equivalent Er(2)Ce6Er6 cuboctahedra, edges with six equivalent Ce(1)Ce9Er3 cuboctahedra, edges with six equivalent Ce(3)Ce9Er3 cuboctahedra,  a faceface with one Ce(2)Ce6Er6 cuboctahedra, faces with six equivalent Er(2)Ce6Er6 cuboctahedra, faces with six equivalent Ce(1)Ce9Er3 cuboctahedra, and faces with six equivalent Ce(3)Ce9Er3 cuboctahedra. In the fourth Ce site, Ce(2) is bonded to three equivalent Er(1), three equivalent Er(2), and six equivalent Ce(2) atoms to form CeCe6Er6 cuboctahedra that share corners with six equivalent Er(3)Ce3Er9 cuboctahedra, corners with six equivalent Ce(2)Ce6Er6 cuboctahedra, corners with six equivalent Ce(3)Ce9Er3 cuboctahedra, edges with six equivalent Er(1)Ce3Er9 cuboctahedra, edges with six equivalent Er(2)Ce6Er6 cuboctahedra, edges with six equivalent Ce(2)Ce6Er6 cuboctahedra,  a faceface with one Er(3)Ce3Er9 cuboctahedra,  a faceface with one Ce(3)Ce9Er3 cuboctahedra, faces with six equivalent Er(1)Ce3Er9 cuboctahedra, faces with six equivalent Er(2)Ce6Er6 cuboctahedra, and faces with six equivalent Ce(2)Ce6Er6 cuboctahedra.
ErCe is beta-derived structured and crystallizes in the trigonal R3m space group. There are five inequivalent Er sites. In the first Er site, Er(1) is bonded to three equivalent Er(3), six equivalent Er(1), and three equivalent Ce(2) atoms to form ErCe3Er9 cuboctahedra that share corners with three equivalent Er(2)Ce6Er6 cuboctahedra, corners with six equivalent Er(1)Ce3Er9 cuboctahedra, corners with six equivalent Ce(1)Ce9Er3 cuboctahedra, edges with three equivalent Er(2)Ce6Er6 cuboctahedra, edges with six equivalent Er(1)Ce3Er9 cuboctahedra, edges with six equivalent Er(3)Ce3Er9 cuboctahedra, edges with six equivalent Ce(2)Ce6Er6 cuboctahedra,  a faceface with one Ce(1)Ce9Er3 cuboctahedra, faces with six equivalent Er(1)Ce3Er9 cuboctahedra, faces with six equivalent Er(3)Ce3Er9 cuboctahedra, and faces with six equivalent Ce(2)Ce6Er6 cuboctahedra. All Er(1)-Er(3) bond lengths are 3.48 Å. All Er(1)-Er(1) bond lengths are 3.55 Å. All Er(1)-Ce(2) bond lengths are 3.46 Å. In the second Er site, Er(2) is bonded to six equivalent Er(2), three equivalent Ce(2), and three equivalent Ce(3) atoms to form ErCe6Er6 cuboctahedra that share corners with three equivalent Er(1)Ce3Er9 cuboctahedra, corners with six equivalent Er(2)Ce6Er6 cuboctahedra, corners with six equivalent Ce(1)Ce9Er3 cuboctahedra, edges with three equivalent Er(1)Ce3Er9 cuboctahedra, edges with six equivalent Er(2)Ce6Er6 cuboctahedra, edges with six equivalent Ce(2)Ce6Er6 cuboctahedra, edges with six equivalent Ce(3)Ce9Er3 cuboctahedra,  a faceface with one Ce(1)Ce9Er3 cuboctahedra, faces with six equivalent Er(2)Ce6Er6 cuboctahedra, faces with six equivalent Ce(2)Ce6Er6 cuboctahedra, and faces with six equivalent Ce(3)Ce9Er3 cuboctahedra. All Er(2)-Er(2) bond lengths are 3.55 Å. All Er(2)-Ce(2) bond lengths are 3.44 Å. All Er(2)-Ce(3) bond lengths are 3.50 Å. In the third Er site, Er(3) is bonded to three equivalent Er(1), six equivalent Er(3), and three equivalent Ce(1) atoms to form ErCe3Er9 cuboctahedra that share corners with three equivalent Ce(3)Ce9Er3 cuboctahedra, corners with six equivalent Er(3)Ce3Er9 cuboctahedra, corners with six equivalent Ce(2)Ce6Er6 cuboctahedra, edges with three equivalent Ce(3)Ce9Er3 cuboctahedra, edges with six equivalent Er(1)Ce3Er9 cuboctahedra, edges with six equivalent Er(3)Ce3Er9 cuboctahedra, edges with six equivalent Ce(1)Ce9Er3 cuboctahedra,  a faceface with one Ce(2)Ce6Er6 cuboctahedra, faces with six equivalent Er(1)Ce3Er9 cuboctahedra, faces with six equivalent Er(3)Ce3Er9 cuboctahedra, and faces with six equivalent Ce(1)Ce9Er3 cuboctahedra. All Er(3)-Er(3) bond lengths are 3.55 Å. All Er(3)-Ce(1) bond lengths are 3.46 Å. In the fourth Er site, Er(2) is bonded to six equivalent Er(2), three equivalent Ce(2), and three equivalent Ce(3) atoms to form ErCe6Er6 cuboctahedra that share corners with three equivalent Er(1)Ce3Er9 cuboctahedra, corners with six equivalent Er(2)Ce6Er6 cuboctahedra, corners with six equivalent Ce(1)Ce9Er3 cuboctahedra, edges with three equivalent Er(1)Ce3Er9 cuboctahedra, edges with six equivalent Er(2)Ce6Er6 cuboctahedra, edges with six equivalent Ce(2)Ce6Er6 cuboctahedra, edges with six equivalent Ce(3)Ce9Er3 cuboctahedra,  a faceface with one Ce(1)Ce9Er3 cuboctahedra, faces with six equivalent Er(2)Ce6Er6 cuboctahedra, faces with six equivalent Ce(2)Ce6Er6 cuboctahedra, and faces with six equivalent Ce(3)Ce9Er3 cuboctahedra. All Er(2)-Er(2) bond lengths are 3.55 Å. All Er(2)-Ce(2) bond lengths are 3.44 Å. All Er(2)-Ce(3) bond lengths are 3.50 Å. In the fifth Er site, Er(2) is bonded to six equivalent Er(2), three equivalent Ce(2), and three equivalent Ce(3) atoms to form ErCe6Er6 cuboctahedra that share corners with three equivalent Er(1)Ce3Er9 cuboctahedra, corners with six equivalent Er(2)Ce6Er6 cuboctahedra, corners with six equivalent Ce(1)Ce9Er3 cuboctahedra, edges with three equivalent Er(1)Ce3Er9 cuboctahedra, edges with six equivalent Er(2)Ce6Er6 cuboctahedra, edges with six equivalent Ce(2)Ce6Er6 cuboctahedra, edges with six equivalent Ce(3)Ce9Er3 cuboctahedra,  a faceface with one Ce(1)Ce9Er3 cuboctahedra, faces with six equivalent Er(2)Ce6Er6 cuboctahedra, faces with six equivalent Ce(2)Ce6Er6 cuboctahedra, and faces with six equivalent Ce(3)Ce9Er3 cuboctahedra. All Er(2)-Er(2) bond lengths are 3.55 Å. All Er(2)-Ce(2) bond lengths are 3.44 Å. All Er(2)-Ce(3) bond lengths are 3.50 Å. There are four inequivalent Ce sites. In the first Ce site, Ce(1) is bonded to three equivalent Er(3), three equivalent Ce(3), and six equivalent Ce(1) atoms to form CeCe9Er3 cuboctahedra that share corners with six equivalent Er(1)Ce3Er9 cuboctahedra, corners with six equivalent Er(2)Ce6Er6 cuboctahedra, corners with six equivalent Ce(1)Ce9Er3 cuboctahedra, edges with six equivalent Er(3)Ce3Er9 cuboctahedra, edges with six equivalent Ce(1)Ce9Er3 cuboctahedra, edges with six equivalent Ce(3)Ce9Er3 cuboctahedra,  a faceface with one Er(1)Ce3Er9 cuboctahedra,  a faceface with one Er(2)Ce6Er6 cuboctahedra, faces with six equivalent Er(3)Ce3Er9 cuboctahedra, faces with six equivalent Ce(1)Ce9Er3 cuboctahedra, and faces with six equivalent Ce(3)Ce9Er3 cuboctahedra. All Ce(1)-Ce(3) bond lengths are 3.42 Å. All Ce(1)-Ce(1) bond lengths are 3.55 Å. In the second Ce site, Ce(2) is bonded to three equivalent Er(1), three equivalent Er(2), and six equivalent Ce(2) atoms to form CeCe6Er6 cuboctahedra that share corners with six equivalent Er(3)Ce3Er9 cuboctahedra, corners with six equivalent Ce(2)Ce6Er6 cuboctahedra, corners with six equivalent Ce(3)Ce9Er3 cuboctahedra, edges with six equivalent Er(1)Ce3Er9 cuboctahedra, edges with six equivalent Er(2)Ce6Er6 cuboctahedra, edges with six equivalent Ce(2)Ce6Er6 cuboctahedra,  a faceface with one Er(3)Ce3Er9 cuboctahedra,  a faceface with one Ce(3)Ce9Er3 cuboctahedra, faces with six equivalent Er(1)Ce3Er9 cuboctahedra, faces with six equivalent Er(2)Ce6Er6 cuboctahedra, and faces with six equivalent Ce(2)Ce6Er6 cuboctahedra. All Ce(2)-Ce(2) bond lengths are 3.55 Å. In the third Ce site, Ce(3) is bonded to three equivalent Er(2), three equivalent Ce(1), and six equivalent Ce(3) atoms to form CeCe9Er3 cuboctahedra that share corners with three equivalent Er(3)Ce3Er9 cuboctahedra, corners with six equivalent Ce(2)Ce6Er6 cuboctahedra, corners with six equivalent Ce(3)Ce9Er3 cuboctahedra, edges with three equivalent Er(3)Ce3Er9 cuboctahedra, edges with six equivalent Er(2)Ce6Er6 cuboctahedra, edges with six equivalent Ce(1)Ce9Er3 cuboctahedra, edges with six equivalent Ce(3)Ce9Er3 cuboctahedra,  a faceface with one Ce(2)Ce6Er6 cuboctahedra, faces with six equivalent Er(2)Ce6Er6 cuboctahedra, faces with six equivalent Ce(1)Ce9Er3 cuboctahedra, and faces with six equivalent Ce(3)Ce9Er3 cuboctahedra. All Ce(3)-Ce(3) bond lengths are 3.55 Å. In the fourth Ce site, Ce(2) is bonded to three equivalent Er(1), three equivalent Er(2), and six equivalent Ce(2) atoms to form CeCe6Er6 cuboctahedra that share corners with six equivalent Er(3)Ce3Er9 cuboctahedra, corners with six equivalent Ce(2)Ce6Er6 cuboctahedra, corners with six equivalent Ce(3)Ce9Er3 cuboctahedra, edges with six equivalent Er(1)Ce3Er9 cuboctahedra, edges with six equivalent Er(2)Ce6Er6 cuboctahedra, edges with six equivalent Ce(2)Ce6Er6 cuboctahedra,  a faceface with one Er(3)Ce3Er9 cuboctahedra,  a faceface with one Ce(3)Ce9Er3 cuboctahedra, faces with six equivalent Er(1)Ce3Er9 cuboctahedra, faces with six equivalent Er(2)Ce6Er6 cuboctahedra, and faces with six equivalent Ce(2)Ce6Er6 cuboctahedra. All Ce(2)-Er(1) bond lengths are 3.46 Å. All Ce(2)-Ce(2) bond lengths are 3.55 Å.