Materials Data on Mg3(Al9Cr)2 by Materials Project

Abstract

Al18Cr2Mg3 is beta-derived structured and crystallizes in the cubic Fd-3m space group. The structure is three-dimensional. there are two inequivalent Mg sites. In the first Mg site, Mg is bonded in a 12-coordinate geometry to two equivalent Mg and twelve equivalent Al atoms. Both Mg–Mg bond lengths are 3.14 Å. All Mg–Al bond lengths are 3.10 Å. In the second Mg site, Mg is bonded in a 12-coordinate geometry to four equivalent Mg and twelve equivalent Al atoms. All Mg–Al bond lengths are 3.21 Å. Cr is bonded to twelve Al atoms to form CrAl12 cuboctahedra that share corners with six equivalent CrAl12 cuboctahedra, edges with eighteen equivalent AlMg3Al8Cr cuboctahedra, and faces with six equivalent AlMg3Al8Cr cuboctahedra. There are six shorter (2.57 Å) and six longer (2.80 Å) Cr–Al bond lengths. There are two inequivalent Al sites. In the first Al site, Al is bonded to three Mg, one Cr, and eight Al atoms to form AlMg3Al8Cr cuboctahedra that share corners with fifteen equivalent AlMg3Al8Cr cuboctahedra, edges with two equivalent AlMg3Al8Cr cuboctahedra, edges with three equivalent CrAl12 cuboctahedra, a faceface with one CrAl12 cuboctahedra, and faces with fifteen equivalent AlMg3Al8Cr cuboctahedra. There are a spread of Al–Al bond distances ranging from 2.69–2.92 Å. In the second Al site, Al is bonded in a 12-coordinate geometry to two equivalent Cr and ten Al atoms. All Al–Al bond lengths are 2.86 Å.