Er6Al3Si crystallizes in the tetragonal I4/mcm space group. There are three inequivalent Er sites. In the first Er site, Er(1) is bonded to two equivalent Al(2) and three equivalent Al(1) atoms to form a mixture of distorted corner and edge-sharing ErAl5 trigonal bipyramids. In the second Er site, Er(2) is bonded in a 6-coordinate geometry to one Al(1), three equivalent Al(2), one Si(1), and one Si(2) atom. In the third Er site, Er(3) is bonded in a 4-coordinate geometry to two equivalent Al(1) and four equivalent Al(2) atoms. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded in a 9-coordinate geometry to two equivalent Er(3), three equivalent Er(1), and four equivalent Er(2) atoms. In the second Al site, Al(2) is bonded in a 10-coordinate geometry to one Er(1), two equivalent Er(3), six equivalent Er(2), and one Al(2) atom. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded in a body-centered cubic geometry to eight equivalent Er(2) atoms. In the second Si site, Si(2) is bonded in a 8-coordinate geometry to eight equivalent Er(2) atoms.
Er6Al3Si crystallizes in the tetragonal I4/mcm space group. There are three inequivalent Er sites. In the first Er site, Er(1) is bonded to two equivalent Al(2) and three equivalent Al(1) atoms to form a mixture of distorted corner and edge-sharing ErAl5 trigonal bipyramids. Both Er(1)-Al(2) bond lengths are 3.11 Å. There are two shorter (3.37 Å) and one longer (3.39 Å) Er(1)-Al(1) bond length. In the second Er site, Er(2) is bonded in a 6-coordinate geometry to one Al(1), three equivalent Al(2), one Si(1), and one Si(2) atom. The Er(2)-Al(1) bond length is 2.98 Å. There are a spread of Er(2)-Al(2) bond distances ranging from 3.11-3.30 Å. The Er(2)-Si(1) bond length is 3.13 Å. The Er(2)-Si(2) bond length is 2.95 Å. In the third Er site, Er(3) is bonded in a 4-coordinate geometry to two equivalent Al(1) and four equivalent Al(2) atoms. Both Er(3)-Al(1) bond lengths are 2.98 Å. There are two shorter (3.00 Å) and two longer (3.65 Å) Er(3)-Al(2) bond lengths. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded in a 9-coordinate geometry to two equivalent Er(3), three equivalent Er(1), and four equivalent Er(2) atoms. In the second Al site, Al(2) is bonded in a 10-coordinate geometry to one Er(1), two equivalent Er(3), six equivalent Er(2), and one Al(2) atom. The Al(2)-Al(2) bond length is 2.74 Å. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded in a body-centered cubic geometry to eight equivalent Er(2) atoms. In the second Si site, Si(2) is bonded in a 8-coordinate geometry to eight equivalent Er(2) atoms.