Ce20Mg19Zn81: A new structure type with a giant cubic cell

Icosa-cerium nona-deca-magnesium henocta-conta-zinc, Ce20Mg19Zn81, synthesized by fritting of the pure elements with subsequent arc melting, crystallizes with an unusually large cubic unit cell [space group F 3m, a = 21.1979 (8) Å] and represents a new structure type among the technologically important family of ternary rare earth-transition metal-magnesium inter-metallics. The majority of atoms (two Ce and five Zn) display.3m site symmetry, two Ce and one Mg atom occupy three 2.mm positions, one Mg and one Zn have 3m site symmetry, one Mg and three Zn atoms sit in..m positions, and one Zn atom is in a general position. The Ce20Mg19Zn81 structure can be described using the geometric concept of nested polyhedral units, by which it consists of four different polyhedral units, viz. A (Zn+Zn4+Zn4+Zn12+Ce6), B (Mg+Zn12+Ce4+Zn24+Ce4), C (Zn4+Zn12+Mg6) and D (Zn4+Zn4+Mg12+Ce6), with the outer construction unit being an octa-hedron or tetra-hedron. All inter-atomic distances in the structure indicate metallic-type bonding. © 2008 International Union of Crystallography