Ce20Mg19Zn81:: a new structure type with a giant cubic cell

Icosacerium nonadecamagnesium henoctacontazinc, Ce(20)Mg(19)Zn(81), synthesized by fritting of the pure elements with subsequent arc melting, crystallizes with an unusually large cubic unit cell [space group F $(4) over bar $ 3m, a = 21.1979 (8) angstrom] and represents a new structure type among the technologically important family of ternary rare earth-transition metal magnesium intermetallics. 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 43m site symmetry, one Mg and three Zn atoms sit in.. m positions, and one Zn atom is in a general position. The Ce(20)Mg(19)Zn(81) structure can be described using the geometric concept of nested polyhedral units, by which it consists of four different polyhedral units, viz. A (Zn+ Zn(4)+ Zn(4)+ Zn(12)+ Ce(6)), B (Mg+ Zn(12)+ Ce(4)+ Zn(24)+ Ce(4)), C (Zn(4)+ Zn(12)+ Mg(6)) and D (Zn(4)+ Zn(4)+ Mg(12)+ Ce(6)), with the outer construction unit being an octahedron or tetrahedron. All interatomic distances in the structure indicate metallic-type bonding.