Crystal structure of a new quaternary Mg–Zn–Ca–Li phase

In course of a study of high strength, ductile alloys based on the Mg–Li system, we have identified a new quaternary phase with a composition of Mg31Zn26Ca13Li8. The structure of this phase was investigated by Transmission Electron Microscopy (TEM) using the Convergent Beam Electron Diffraction (CBED) technique. Full atomic model is proposed using direct methods applied to powder X-ray diffraction data. The phase has a cubic primitive unit cell with lattice parameter a   = 9.386(8)Å and its crystal symmetry belongs to the Pm3¯ (No. 200) space group. The unit cell of the new phase exhibits a new structure type, which is a variant of the Mg2Zn11 structure. The reliability factors characterizing the Rietveld refinement procedure are: Rp = 8.6%, Rwp = 12.4%, RB = 6.9% and Rf = 4.4%.

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► The structure a quaternary phase Mg–Zn–Ca–Li was determined by a combination of electron crystallography and X-ray powder diffraction methods.
► Unit cell geometry was identified by electron diffraction methods.
► The general symmetry and point group was determined by CBED.
► Space group was determined combining X-ray powder diffraction and electron diffraction data.
► Full atomic model is proposed based on direct methods applied to X-ray powder diffraction data.