Location of Zn within the Mg12(LaxCe1−x) lattice by X-ray incoherent channelling patterns

Systematic electron diffraction studies on intermetallic precipitates formed within a lightweight Mg–RE–Zn alloy (RE = La or Ce) identify these to be of structural type Mn12Th (space group I4/mmm). Analytical electron microscopy yields an overall composition of Mg12(LaxCe1−x) with x ~ 0.43, with 1 at.% Zn incorporated within the lattice. Variations in characteristic X-ray emission rates, as an electron beam is rocked near zone-axis orientations, are used to form two-dimensional channelling patterns, termed X-ray incoherent channelling patterns. This channelling contrast enables a specific sublattice site that is occupied by Zn to be unambiguously identified within the Mg12RE lattice. The particular sublattice site is denoted by the Wyckoff letter f, and is one of the three different Mg sublattice sites f, i and j. Of these three sites, the Wigner–Seitz cell that is centred on the f sublattice site has the largest Mg–RE interatomic distance, and therefore the f site is expected to be favoured for accommodating the substitution of a larger Zn atom.