Osmium and magnesium: structural segregation in the rare earth-rich intermetallics RE ₄OsMg (RE=La–Nd, Sm) and RE ₉ TMg₄ (RE=Gd, Tb)

Abstract

Ternary rare earth metal-rich intermetallic phases containing osmium and magnesium were obtained by induction melting of the elements in sealed niobium ampoules under argon followed by annealing in muffle furnaces. The large rare earth elements form the series of Gd4RhIn-type (F4̅3m) intermetallics RE4OsMg with RE = La–Nd and Sm, while the smaller rare earth metals gadolinium and terbium form the Y9CoMg4-type (P63/mmc) phases Gd9OsMg4 and Tb9OsMg4. All samples were characterized by X-ray powder diffraction (Guinier technique). The structures of Ce4Os0.973Mg1.027 (a = 1406.54(7) pm, wR2 = 0.0478), Nd4Os0.978Mg1.022 (a = 1402.00(7) pm, wR2 = 0.0463), Sm4Os0.920Mg1.080 (a = 1387.33(5) pm, wR2 = 0.0378) and Gd9OsMg4 (a = 971.01(5), c = 980.43(5) pm, wR2 = 0.0494) were refined from single-crystal X-ray diffractometer data. The three RE4OsMg phases show small degrees of Os/Mg mixing, as is frequently observed for Rh/In in Gd4RhIn-type intermetallics. The basic building units in both structures are osmium-centered RE6 trigonal prisms that are condensed with empty RE6 octahedra. The magnesium atoms in both types build Mg4 tetrahedra. The latter are isolated (312 pm Mg–Mg in Ce4OsMg) and incorporated within the three-dimensional network of prisms and octahedra in the RE4OsMg phases while one observes rows of corner- and face-sharing tetrahedra in Gd9OsMg4 (305 and 314 pm Mg–Mg). In both structure types direct Os–Mg bonding is not observed.

(Ca, Eu, Yb)₂₃Cu₇Mg₄ as a Step towards the Structural Generalization of Rare Earth-Rich Intermetallics

“…Slabs of each parent type are alternatively stacked along the c-direction, fulfilling the crystal space with no gaps neither need of "gluing" atoms (see Figure 6a). Slabs, possessing the same p3m1 layer symmetry, are joined by a common corrugated layer composed exclusively by R atoms, showing two types of nodes represented by (3 6 ) 1 ;(3 2 434) 6 Schläfli notation (see Figure 6b).…”

{Ca, Eu, Yb}23Cu7Mg4 as a Step towards the Structural Generalization of Rare Earth-Rich Intermetallics

“…The component interaction in RTX intermetallic systems (R = rare earth metal; T = transition metal; X = other metal) results in many ternary compounds with recurrent stoichiometries in different concentration ranges. These compounds have been widely studied both for their applicative and fundamental properties [1][2][3][4][5][6][7][8][9][10][11][12], and they represent an ever-growing database for studying structural relationships, aiming for simplified descriptions and rational generalizations.…”

Formation of the Sub-oxide Sc4Au2O1–x and the Drastically Negative 27Al NMR Shift in Sc2Al

“…Of the latter, over 200 compounds were reported for different combinations of rare-earth and transition metals. Besides the respective aluminum compounds, ,− the isostructural indium, ,, cadmium ,,− and magnesium ,− representatives have also been reported. Of these, e.g., Eu 4 PdMg exhibits exceptional good magnetocaloric properties in a large temperature window .…”