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DOE OSTI2020

Materials Data on Sm2Fe17N3 by Materials Project

Sm2Fe17N3 crystallizes in the trigonal R-3m space group. The structure is three-dimensional. Sm is bonded in a trigonal planar geometry to four Fe and three equivalent N atoms. There are one shorter (3.11 Å) and three longer (3.33 Å) Sm–Fe bond lengths. All Sm–N bond lengths are 2.51 Å. There are four inequivalent Fe sites. In the first Fe site, Fe is bonded to two equivalent Sm and ten Fe atoms to form FeSm2Fe10 cuboctahedra that share corners with four equivalent FeSm2Fe10 cuboctahedra, corners with two equivalent NSm2Fe4 octahedra, faces with four equivalent FeSm2Fe10 cuboctahedra, and faces with four equivalent NSm2Fe4 octahedra. The corner-sharing octahedral tilt angles are 44°. There are a spread of Fe–Fe bond distances ranging from 2.46–2.67 Å. In the second Fe site, Fe is bonded in a single-bond geometry to four Fe and one N atom. Both Fe–Fe bond lengths are 2.72 Å. The Fe–N bond length is 1.89 Å. In the third Fe site, Fe is bonded in a single-bond geometry to three Fe and one N atom. The Fe–Fe bond length is 2.66 Å. The Fe–N bond length is 1.92 Å. In the fourth Fe site, Fe is bonded in a 2-coordinate geometry to one Sm and thirteen Fe atoms. The Fe–Fe bond length is 2.36 Å. N is bonded to two equivalent Sm and four Fe atoms to form NSm2Fe4 octahedra that share corners with two equivalent FeSm2Fe10 cuboctahedra, corners with four equivalent NSm2Fe4 octahedra, and faces with four equivalent FeSm2Fe10 cuboctahedra. The corner-sharing octahedral tilt angles are 60°.

36 MATERIALS SCIENCE↗

DOE OSTI2025

Minimizing particle aggregation in Sm 2 Fe 17 N 3 powders: A CaO-assisted reduction-diffusion approach

We report a novel synthesis of Sm 2 Fe 17 N 3 powders using a CaO-assisted reduction-diffusion (RD) approach. CaO plays a crucial role during mechanochemical processing – acting both as a dispersant and a surface coating agent, which helps to prevent agglomeration due to sintering of Sm 2 Fe 17 particles during the RD step. Together with the added dispersant, the CaO by-product formed during RD can be easily removed in the washing step resulting in fewer aggregated Sm 2 Fe 17 N 3 particles and lower oxygen contamination in the final product. The impact of varying CaO amounts was examined, and synthesis conditions were optimized to achieve phase-pure Sm 2 Fe 17 N 3 powders with less aggregation of magnetic particles. The powders synthesized with addition of 1 wt% CaO as dispersant exhibited the highest hard-magnetic properties: a coercivity (H c ) of 10.7 kOe and a maximum energy product ((BH) max ) of 17.3 MGOe. By densifying the Sm 2 Fe 17 N 3 powders using high-pressure spark plasma sintering, a bulk magnet with a (BH) max of 21.1 MGOe with 88 % of theoretical density was produced. In conclusion, reducing aggregation of the Sm 2 Fe 17 N 3 increases coercivity and remanence of these magnets.

36 MATERIALS SCIENCE↗

DOE OSTI2026

Role of washing solvents in defining the magnetic performance of Sm 2 Fe 17 N 3 obtained by reduction diffusion

Calciothermic reduction-diffusion (RD) is one of the leading synthesis methods for Sm 2 Fe 17 N 3 (SmFeN), but sintering of such RD-derived powders is hampered by oxidation and CaO byproducts. Here, we systematically evaluate how post-synthesis washing solvents govern powder chemistry and magnetic performance. RD-synthesized SmFeN powder was washed with several aqueous and non-aqueous solvents using identical washing protocols. This was followed by an assessment of both the as-washed powder as well as after annealing at 425 °C. Phase content was quantified by synchrotron PXRD and Rietveld refinement and SEM/EDS. The oxygen content of the powders was determined via inert gas fusion and the magnetization by DC magnetometry. While all aqueous-based solutions were able to remove CaO, the non-aqueous solutions were only effective with extended washing times. Prior to annealing, the crystalline phases and magnetic properties of the as-washed powders were largely the same regardless of washing solvent. However, differences emerge after annealing, where water-based washing markedly lowers the coercivity (H c ~3.8-4.3 kOe). In contrast, non-aqueous NH 4 Cl-methanol washing protocols were more effective in preserving coercivity (H c ~4.9-5.9 kOe). We attribute this to lower oxygen content in the non-aqueous samples (~9,400 ppm v ~6,400 ppm, respectively) which in turn reduced the formation of α-Fe during annealing. These results highlight the importance of solvent choice in washing RD-synthesized SmFeN and demonstrate that non-aqueous protocols, which better limit oxidation, outperform aqueous solvents despite the need for longer washing times.

36 MATERIALS SCIENCE↗