Crystallochemistry of the novel two-layer RECuMg4 (RE=La, Tb) ternary compounds

The crystal structures of the new ternary compounds LaCuMg4 and TbCuMg4 were studied by X-ray powder diffraction and single-crystal methods, respectively. Scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDXS) was used for examining microstructure and phase composition. LaCuMg4 crystallizes in the UCoAl4 structure type (space group P6¯2m, Pearson code hP18, a=1.03911(1), c=0.45126(1) nm, Z=3, RF=0.0654), while TbCuMg4 exhibits a new structure (space group Cmmm, Pearson code oS48, a=1.35797(6), b=2.03333(9), c=0.39149(2) nm, Z=8, wR2=0.0426). Both structures represent a family of two-layer compounds. All interatomic distances indicate metallic type bonding. The structural peculiarities of these compounds and their relations are discussed.

Graphical abstractSlightly distorted body centered Mg blocks as structural motifs in the LaCuMg4 and TbCuMg4 compounds.Figure optionsDownload full-size imageDownload as PowerPoint slide