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5 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Thin-Film Stabilization and Magnetism of η -Carbide-Type Iron Nitrides

Transition-metal nitrides in ..eta..-carbide-type structures exhibit unusual bonding motifs and proximity to magnetic instabilities. Yet they remain unexplored in thin-film form due to the difficulty of stabilizing nitrogen-poor ternaries among competing phases. Here, we report the thin-film synthesis and phase-stability mapping of the ..eta..-nitride systems Fe-W-N and Fe-Mo-N. Amorphous Fe-M-N (M = W, Mo) combinatorial libraries deposited by reactive cosputtering crystallize upon rapid thermal annealing, enabling systematic identification of synthesis windows as a function of composition and annealing temperature. Using laboratory powder X-ray diffraction and synchrotron grazing incidence wide-angle X-ray scattering, we establish that Fe 3 Mo 3 N-based ..eta..-carbide phases form over a substantially broader compositional and thermal range than W-based compositions, where ..eta.. structures are stabilized only when the films are Fe-rich. These trends are rationalized using mixed chemical-potential vs composition phase diagrams that capture the narrow nitrogen chemical-potential stability of ..eta..-nitrides. Magnetic measurements reveal that ferromagnetism is induced in Fe-rich Fe 3.54 Mo 2.46 N with a small exchange-bias-like response that is absent in Fe 3 W 3 N-based compositions, highlighting the sensitivity of magnetic behavior to modest deviations from stoichiometry. This work establishes practical thin-film synthesis routes for ..eta..-nitride materials and demonstrates how composition can be tuned to access emergent magnetic phenomena in these complex nitrides.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Fe3Mo3N by Materials Project

Fe3Mo3N crystallizes in the cubic Fd-3m space group. The structure is three-dimensional. Mo is bonded in a 2-coordinate geometry to six Fe and two equivalent N atoms. There are four shorter (2.72 Å) and two longer (2.73 Å) Mo–Fe bond lengths. Both Mo–N bond lengths are 2.13 Å. There are two inequivalent Fe sites. In the first Fe site, Fe is bonded to six equivalent Mo and six equivalent Fe atoms to form FeFe6Mo6 cuboctahedra that share edges with six equivalent NMo6 octahedra and faces with six equivalent FeFe6Mo6 cuboctahedra. All Fe–Fe bond lengths are 2.35 Å. In the second Fe site, Fe is bonded in a distorted q6 geometry to six equivalent Mo and six Fe atoms. All Fe–Fe bond lengths are 2.40 Å. N is bonded to six equivalent Mo atoms to form NMo6 octahedra that share corners with six equivalent NMo6 octahedra and edges with six equivalent FeFe6Mo6 cuboctahedra. The corner-sharing octahedral tilt angles are 47°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Fe2Mo4N by Materials Project

Fe2Mo4N crystallizes in the cubic Fd-3m space group. The structure is three-dimensional. there are two inequivalent Mo sites. In the first Mo site, Mo is bonded in a 6-coordinate geometry to six equivalent Fe atoms. All Mo–Fe bond lengths are 2.42 Å. In the second Mo site, Mo is bonded in a 2-coordinate geometry to four equivalent Fe and two equivalent N atoms. There are two shorter (2.71 Å) and two longer (2.86 Å) Mo–Fe bond lengths. Both Mo–N bond lengths are 2.13 Å. Fe is bonded in a 12-coordinate geometry to nine Mo and three equivalent Fe atoms. All Fe–Fe bond lengths are 2.57 Å. N is bonded to six equivalent Mo atoms to form corner-sharing NMo6 octahedra. The corner-sharing octahedral tilt angles are 42°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Fe4Mo2N by Materials Project

Mo2Fe4N crystallizes in the tetragonal I-4m2 space group. The structure is three-dimensional. there are three inequivalent Mo sites. In the first Mo site, Mo is bonded in a 2-coordinate geometry to six Fe and two equivalent N atoms. There are a spread of Mo–Fe bond distances ranging from 2.61–2.75 Å. Both Mo–N bond lengths are 2.08 Å. In the second Mo site, Mo is bonded in a 2-coordinate geometry to six Fe and two equivalent N atoms. There are a spread of Mo–Fe bond distances ranging from 2.62–2.73 Å. Both Mo–N bond lengths are 2.14 Å. In the third Mo site, Mo is bonded in a distorted bent 150 degrees geometry to six Fe and two equivalent N atoms. There are a spread of Mo–Fe bond distances ranging from 2.63–2.73 Å. Both Mo–N bond lengths are 2.08 Å. There are four inequivalent Fe sites. In the first Fe site, Fe is bonded to four Mo and eight Fe atoms to form distorted FeFe8Mo4 cuboctahedra that share edges with six equivalent NFe2Mo4 octahedra and faces with six equivalent FeFe8Mo4 cuboctahedra. There are a spread of Fe–Fe bond distances ranging from 2.31–2.75 Å. In the second Fe site, Fe is bonded in a 12-coordinate geometry to four Mo and eight Fe atoms. There are a spread of Fe–Fe bond distances ranging from 2.50–2.75 Å. In the third Fe site, Fe is bonded in a 12-coordinate geometry to four Mo and eight Fe atoms. There are a spread of Fe–Fe bond distances ranging from 2.55–2.58 Å. In the fourth Fe site, Fe is bonded in a distorted bent 120 degrees geometry to six Fe and two equivalent N atoms. Both Fe–N bond lengths are 2.02 Å. N is bonded to four Mo and two equivalent Fe atoms to form NFe2Mo4 octahedra that share corners with six equivalent NFe2Mo4 octahedra and edges with six equivalent FeFe8Mo4 cuboctahedra. The corner-sharing octahedra tilt angles range from 40–46°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Fe3Mo5N8 by Materials Project

Mo5Fe3N8 is Caswellsilverite-like structured and crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are three inequivalent Mo3+ sites. In the first Mo3+ site, Mo3+ is bonded to six N3- atoms to form distorted MoN6 pentagonal pyramids that share corners with four equivalent MoN6 octahedra, corners with eight FeN6 octahedra, edges with six MoN6 pentagonal pyramids, and faces with two FeN6 octahedra. The corner-sharing octahedra tilt angles range from 45–46°. There are a spread of Mo–N bond distances ranging from 2.12–2.15 Å. In the second Mo3+ site, Mo3+ is bonded to six N3- atoms to form distorted MoN6 pentagonal pyramids that share corners with two equivalent MoN6 octahedra, corners with ten FeN6 octahedra, edges with six MoN6 pentagonal pyramids, a faceface with one MoN6 octahedra, and a faceface with one FeN6 octahedra. The corner-sharing octahedra tilt angles range from 44–47°. There are a spread of Mo–N bond distances ranging from 2.11–2.14 Å. In the third Mo3+ site, Mo3+ is bonded to six N3- atoms to form MoN6 octahedra that share corners with twelve MoN6 pentagonal pyramids, edges with two equivalent MoN6 octahedra, edges with four equivalent FeN6 octahedra, and faces with two equivalent MoN6 pentagonal pyramids. There are two shorter (2.18 Å) and four longer (2.21 Å) Mo–N bond lengths. There are two inequivalent Fe3+ sites. In the first Fe3+ site, Fe3+ is bonded to six N3- atoms to form FeN6 octahedra that share corners with twelve MoN6 pentagonal pyramids, edges with two equivalent FeN6 octahedra, edges with four equivalent MoN6 octahedra, and faces with two equivalent MoN6 pentagonal pyramids. There are two shorter (2.20 Å) and four longer (2.22 Å) Fe–N bond lengths. In the second Fe3+ site, Fe3+ is bonded to six N3- atoms to form FeN6 octahedra that share corners with twelve MoN6 pentagonal pyramids, edges with six equivalent FeN6 octahedra, and faces with two MoN6 pentagonal pyramids. There are a spread of Fe–N bond distances ranging from 2.09–2.14 Å. There are four inequivalent N3- sites. In the first N3- site, N3- is bonded to four Mo3+ and two equivalent Fe3+ atoms to form distorted NFe2Mo4 pentagonal pyramids that share corners with nine NFe2Mo4 pentagonal pyramids, edges with nine NFe2Mo4 pentagonal pyramids, and a faceface with one NFe3Mo3 pentagonal pyramid. In the second N3- site, N3- is bonded to five Mo3+ and one Fe3+ atom to form distorted NFeMo5 pentagonal pyramids that share corners with nine NFeMo5 pentagonal pyramids, edges with nine NFe2Mo4 pentagonal pyramids, and a faceface with one NFe3Mo3 pentagonal pyramid. In the third N3- site, N3- is bonded to three Mo3+ and three equivalent Fe3+ atoms to form distorted NFe3Mo3 pentagonal pyramids that share corners with nine NFe2Mo4 pentagonal pyramids, edges with nine NFe3Mo3 pentagonal pyramids, and a faceface with one NFeMo5 pentagonal pyramid. In the fourth N3- site, N3- is bonded to three Mo3+ and three equivalent Fe3+ atoms to form distorted NFe3Mo3 pentagonal pyramids that share corners with nine NFe2Mo4 pentagonal pyramids, edges with nine NFe3Mo3 pentagonal pyramids, and a faceface with one NFe2Mo4 pentagonal pyramid.

36 MATERIALS SCIENCE↗