Materials Data on CaMg2 by Materials Project

Abstract

Mg2Ca is Bergman Structure: Mg32(Al,Zn)49 Bergman-derived structured and crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. Ca is bonded to three equivalent Ca and nine Mg atoms to form distorted CaCa3Mg9 cuboctahedra that share corners with six equivalent CaCa3Mg9 cuboctahedra, corners with six equivalent MgCa5Mg7 cuboctahedra, edges with four equivalent CaCa3Mg9 cuboctahedra, edges with five equivalent MgCa5Mg7 cuboctahedra, faces with six equivalent CaCa3Mg9 cuboctahedra, and faces with eight equivalent MgCa5Mg7 cuboctahedra. There are two shorter (3.48 Å) and one longer (3.59 Å) Ca–Ca bond lengths. There are a spread of Ca–Mg bond distances ranging from 3.40–3.58 Å. There are two inequivalent Mg sites. In the first Mg site, Mg is bonded to five equivalent Ca and seven Mg atoms to form distorted MgCa5Mg7 cuboctahedra that share corners with six equivalent CaCa3Mg9 cuboctahedra, corners with six equivalent MgCa5Mg7 cuboctahedra, edges with five equivalent CaCa3Mg9 cuboctahedra, edges with six equivalent MgCa5Mg7 cuboctahedra, faces with five equivalent MgCa5Mg7 cuboctahedra, and faces with eight equivalent CaCa3Mg9 cuboctahedra. There are a spread of Mg–Mg bond distances ranging from 3.20–3.48 Å. In the second Mg site, Mg is bonded in a 11-coordinate geometry to four equivalent Ca and seven Mg atoms. There are two shorter (3.12 Å) and two longer (3.48 Å) Mg–Mg bond lengths.