Rare earth–copper–magnesium compounds RECu9Mg2 (RE=Y, La–Nd, Sm–Ho, Yb) with ordered CeNi3-type structure

A series of ternary compounds RECu9Mg2 (RE=Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Yb) have been synthesized via induction melting of elemental metal ingots followed by annealing at 400 °C for 4 weeks. Scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDXS) was used for examining microstructure and phase composition. These phases crystallize with an ordered version of the binary hexagonal structure type first reported for CeNi3. The crystal structure was solved for TbCu9Mg2 from single crystal X-ray counter data (TbCu9Mg2-structure type, P63/mmc–space group, hP24–Pearson symbol, a=0.49886 (7) nm, c=1.61646 (3) nm, RF=0.0474 for 190 unique reflections). The Rietveld refinement of the X-ray powder diffraction patterns of RECu9Mg2 confirmed the same crystal structure for the reported rare earth metals. The unit cell volumes for RECu9Mg2 smoothly follow the lanthanide contraction. The existence of a RECu9Mg2 phase was excluded for RE=Er and Tm under the investigated experimental conditions.