Phase relationships of the La–Ni–Mg system at 500 °C from 66.7 to 100 at.% Ni

The La–Ni–Mg isothermal section at 500 °C was investigated in the region from 66.7 to 100 at.% Ni by means of scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDXS) and X-ray powder diffraction (XRPD). Phase relations were established in this composition range.The binary boundary phases MgNi2, LaNi5 and La7Ni16 do not dissolve any appreciable amount of the third element. Three solid solutions were found to exist, extending at a constant Ni content. The range of homogeneity (0 < x ≤ 0.60) and crystal structure (cF24-MgCu4Sn) of (La1−xMgx)Ni2 were confirmed. (La1−xMgx)2Ni7 (0 ≤ x ≤ 0.13) derives from the binary La2Ni7 (L.T.), of hexagonal hP36-Ce2Ni7 type structure. (La1−xMgx)Ni3 (0 ≤ x ≤ 0.67) forms from the binary LaNi3, whose structure is trigonal hR36-PuNi3. For x = 0.67 the stoichiometry LaMg2Ni9 is obtained, which was already reported in the literature as a ternary ordered phase with PuNi3 type structure.