Isolation of the New Cubic Phases RE₄FeGa_12-xGe_x (RE = Sm, Tb; x = 2.5) from Molten Gallium:  Single-Crystal Neutron Diffraction Study of the Ga/Ge Distribution

Abstract

The compounds RE4FeGa(12-x)Ge(x) (RE = Sm, Tb) were discovered in reactions employing molten Ga as a solvent at 850 degrees C. However, the isostructural Y4FeGa(12-x)Ge(x) was prepared from a direct combination reaction. The crystal structure is cubic with space group Imm, Z = 2, and a = 8.657(4) A and 8.5620(9) A for the Sm and Tb analogues, respectively. Structure refinement based on full-matrix least squares on F(o)2 resulted in R1 = 1.47% and wR2 = 4.13% [I > 2(I)] for RE = Sm and R1 = 2.29% and wR2 = 7.12% [I > 2(I)] for RE = Tb. The compounds crystallize in the U4Re7Si6 structure type, where the RE atoms are located on 8c (1/4, 1/4, 1/4) sites and the Fe atoms on 2a (0, 0, 0) sites. The distribution of Ga and Ge in the structure, investigated with single-crystal neutron diffraction on the Tb analogue, revealed that these atoms are disordered over the 12d (1/4, 0, 1/2) and 12e (x, 0, 0) sites. The amount of Ga/Ge occupying the 12d and 12e sites refined to 89(4)/11 and 70(4)/30%, respectively. Transport property measurements indicate that these compounds are metallic conductors. Magnetic susceptibility measurements and Mössbauer spectroscopy performed on the Tb analogue show a nonmagnetic state for Fe, while the Tb atoms carry a magnetic moment corresponding to a mu(eff) of 9.25 mu(B).

The Metal Flux: A Preparative Tool for the Exploration of Intermetallic Compounds

“…Table 3 summarizes some of the ternary and quaternary compounds synthesized or discovered with a gallium flux. The compounds RE 4 FeGa 12− x Ge x 230 were discovered during investigations of reactions in liquid gallium involving RE , T , and Ge, where RE =Y, Ce, Sm, Gd, Tb; and T =Fe, Co, Ni, or Cu. These systems were investigated at various metal ratios and different heating regimes.…”

Crystal growth and properties of Ln2Ag1−xGa10−y (Ln=La, Ce), a disordered variant of the Ce2NiGa10-structure type

“…Here M¼Ag+Ga and the shaded atoms are partially occupied. [10], Ln 2 MGa 9 Ge 2 (Ln ¼Ce, Sm; M¼Ni, Co) [47], Ln 3 Ni 3 Ga 8 Ge 3 (Ln¼lanthanide) [48], LnMGa 3 Ge (Ln ¼lanthanide; M¼Ni, Co) [6,7,48], and Ln 4 FeGa 12 À x Ge x (Ln ¼Sm, Tb; x¼2.5) [49] have been the focus of recent work. The disorder in the CaF 2 -type gallium segment can be rationalized by the tendency of gallium to adopt a coordination of four.…”

Metallische Schmelzen – Reaktionsmedien zur Präparation intermetallischer Verbindungen

“…Tabelle 3 fasst einige ternäre und quaternäre Verbindungen zusammen, die ausgehend von einer Galliumschmelze entdeckt wurden. Die Verbindungen RE 4 FeGa 12− x Ge x 230 wurden im Verlauf von Untersuchungen entdeckt, bei denen in flüssigem Gallium die Komponenten RE , T und Ge ( RE =Y, Ce, Sm, Gd, Tb; T =Fe, Co, Ni, Cu) als Ausgangsstoffe eingesetzt wurden. Die betreffenden Systeme wurden ausgehend von verschiedenen Mischungsverhältnissen der Metalle bei unterschiedlichen Glühbedingungen untersucht.…”