Novel ternary iron-rich, rare-earth iron silicides: R3(Fe1−x Si x )22 (x ∼ 0.16)

Abstract

In our search for new ternary rare-earth (R) iron silicon intermetallic compounds, a novel ternary phase with the chemical formula R3Fe18.5Si3.5 has been identified with the R∶Fe∶Si ratio in the range of 12–15∶74–78∶10–12. We have studied compounds with R=Gd, Tb, Dy, Ho, Er, Tm and Lu. All of the samples, except for R=Lu, form the new ternary phase3–22. X-ray diffraction data suggest that for R=Gd and Tb, the crystal structure is the rhombohedral Th2Zn17-type structure and for R=Dy, Ho, Er and Tm, the hexagonal Th2Ni17-type structure. We suggest that a 1/4 replacement of the “R” sites by Fe(Si) dumbbells in the CaCu5-type structure leads to the new3–22 phase, which is an ordered version of the TbCu7-type structure.57Fe Mossbauer spectroscopy has been used to determine the hyperfine parameters of the57Fe nuclei in the3–22 compounds. At 295 K, the average hyperfine field of the new3–22 phase ranges from 19.8 T (R=Ho) to 22.2 T (R=Gd). Thermogravimetric analysis (TGA) of these compounds gives Curie temperatures in the range 467 K (Tm)–549 K (Gd). Furthermore, our Mossbauer analysis enables us to investigate the preferential site occupancy shown by Si in these structures.