Neutron powder diffraction and first-principles computational studies of CuLi xMg 2−x ( x≅0.08), CuMg 2, and Cu 2Mg

Abstract

A small addition of Li changes the orthorhombic structure of CuMg 2 to hexagonal CuLi x Mg 2− x ( x=0.08). Determining the Li content of the ternary phase and Li atomic positions was our main objective for this work. For this reason we performed neutron diffraction at several different temperatures below and above room temperature. The results obtained on two neutron powder diffractometers were compared with X-ray diffraction (XRD) data, and with first-principles calculations. The first-principles calculations are in good agreement with Rietveld-refined data from neutron diffraction, but do not show a marked preference for one of several possible Li sites. The pair distribution function (PDF) fitting is consistent with Li substituting only Mg1 (1/2, 0, z). Interstitial spaces in the structure of CuMg 2 and of CuLi x Mg 2− x were also considered, but are unlikely to be occupied by Li. Neutron diffraction data for binary CuMg 2 and Cu 2Mg were also obtained.