Rare Earth (RE) Gallides with Closely Related Compositions: REIrGa and RE₆Ir₅Ga₇

Abstract

The ternary rare‐earth iridium gallides RE6Ir5Ga7 (RE = Sc, Y, Nd, Sm, Gd – Tm, and Lu) were synthesized from the elements by arc‐melting or by induction melting in sealed niobium ampoules. The samples were structurally characterized by X‐ray powder diffraction. The structure of Sc6Ir5Ga7 was refined from single‐crystal X‐ray diffractometer data: Yb6Ir5Ga7 (Nb6.4Ir4Al7.6) type, P63/mcm, a = 912.84(7), c = 828.07(6) pm, wR2 = 0.0362, 504 F2 values and 22 variables. The RE6Ir5Ga7 gallides crystallize with a fully ordered superstructure of the hexagonal Laves phase MgZn2. The zinc substructure consists of ordered and condensed Ir3Ga and IrGa3 tetrahedra. Further phase analytical studies in the RE‐Ir‐Ga systems led to the new equiatomic gallides SmIrGa and LuIrGa with the orthorhombic, TiNiSi type structure, space group Pnma. The samarium compound shows a pronounced solid solution SmIr1–xGa1+x, which was confirmed by single crystal structure refinements for SmIr0.95Ga1.05, SmIr0.69Ga1.31 and SmIr0.55Ga1.45. The RE6Ir5Ga7 and REIrGa gallides show pronounced covalent Ir–Ga bonding.

Laves phases: superstructures induced by coloring and distortions

“…[64] Yb 6 Ir 5 Ga 7 [122] was the first example of that superstructure variant with a complete ordering on the tetrahedral substructure. This was meanwhile also observed for the rare earth-based series RE 6 Ir 5 Ga 7 [127] and RE 6 T 5 Al 7 (T = Ru, Ir). [92] The reason for superstructure formation is the different coloring within the rows of face-and corner-sharing tetrahedra.…”

On the Ytterbium Valence and the Physical Properties in Selected Intermetallic Phases

“…The superstructure formation leads to a small deviation. The correct model was solved for Yb 6 Ir 5 Ga 7 (space group P 6 3 / mcm ) and the series of gallides RE 6 Ir 5 Ga 7 . , Shortly later, also the aluminum containing RE 6 T 5 Al 7 phases ( RE = Sc, Y, Ce–Nd, Sm, Gd–Lu; T = Ru, Ir) have been structurally characterized. With respect to the physical properties, one must differentiate between the fully ordered 6–5–7 phases and solid solutions where mixed occupied sites occur.…”

On the RE2TiAl3 (RE = Y, Gd–Tm, Lu) Series—The First Aluminum Representatives of the Rhombohedral Mg2Ni3Si Type Structure

“…Furthermore, Yb 6 Ir 5 Ga 7 [36] represents a √ 3 × √ 3 superstructure of the hexagonal MgZn 2 -type structure, allowing for a coloration of the tetrahedral strands of the prototype. To date, the iridium gallides RE 6 Ir 5 Ga 7 (RE = Sc, Y, Nd, Sm, Gd-Lu) [36,37] and the RE 6 T 5 Al 7 series (RE = Sc, Y, Ce-Nd, Sm, Gd-Lu, T = Ru, Ir) [38] have been reported. Finally, a rhombohedral ordered variant of the MgCu 2 type is observed for the Mg 2 Ni 3 Si (R3m) type structure [39], realized, e.g., for the gallides RE 2 Rh 3 Ga (RE = Y, La-Nd, Sm, Gd-Er) [40], the silicides RE 2 Rh 3 Si (RE = Ce, Pr, Er) [41][42][43] and U 2 Ru 3 Si [44], or the germanides RE 2 T 3 Ge (RE = Y, Pr, Sm, Er) [41,45], U 2 Ru 3 Ge [44], and Ca 2 Pd 3 Ge [46].…”