New Intermetallic Compounds RE₄Co₂Mg₃ (RE = Pr, Gd, Tb, Dy) – Syntheses, Structure, and Chemical Bonding

Abstract

The magnesium compounds RE 4 Co 2 Mg 3 (RE = Pr, Gd, Tb, Dy) were prepared by induction melting of the elements in sealed tantalum tubes. The samples were studied by powder X-ray diffraction. The structures of the gadolinium and of the terbium compound were refined from single crystal diffractometer data:

Phase equilibria in the Tb-Mg-Co system at 500°C, crystal structure and hydrogenation properties of selected compounds

“…The refined lattice parameters for both Tb 4 Mg 3 Co 2 and Tb 4 MgCo compounds (see Table. 2) are in good agreement with the published data [38,39]. We also confirmed the deviation from a stoichiometric Table 3.…”

“…group P6 3 mc). The crystal structure of the compound ~La 38 Co 55 Mg 7 remains undetermined. The existence of the La 2 Co 17-x Mg x phase was reported and indicates the stabilizing role of magnesium on the formation of the binary phase La 2 Co 17 .…”

Rare earth–transition metal–magnesium compounds—An overview

“…All these Co-Nd distances are close to the sum of the covalent radii of 280 pm, and we can safely assume strong Co-Nd bonding. This was underlined by recent electronic structure calculations [40].…”

“…Instead we observed another intergrowth structure, the Nd 4 Co 2 Mg 3 type [38], space group P2/m, which can be considered as a 1:3 intergrowth variant of distorted AlB 2 and CsCl related slabs of compositions NdCo 2 and NdMg. This monoclinic structure type is formed also with RE ¼ Pr, Sm, Gd, Tb, and Dy [40]. The Co 2 dumb-bells in the neodymium compound have Co-Co distances of 237 pm, somewhat shorter than the average Co-Co distance of 250 pm in hcp cobalt [63].…”

The novel intermetallic phases TbNiMg and Tb4+xNi2Mg3−x (x = 0.2): Synthesis, crystal structure and peculiarities

“…The Tb 4þx Ni 2 Mg 3Àx phase could be assigned to the series of general formula R 0 2mþn X 2n R 00 2m firstly described by Kuz'ma [25], which is composed of two kinds of constituent blocks: AlB 2 -type (whose number is indicated by n in the formula) and CsCl-type cubes (m in the formula). A branch of this series, containing beside the Tb 4þx Ni 2 Mg 3Àx phase also the recently published Nd 4 Co 2 Mg 3 [26] and Nd 11 Pd 4 In 9 [27] intermetallic compounds together with Lu 5 Ni 2 In 4 [28] and Mo 2 FeB 2 [14] structure types, can be individuated as a planar intergrowth set because the two-dimensional segments of the constituent fragments are stacked within a stacking plane (Fig. 5b).…”