A first-principles reassessment of the Fe-N phase diagram in the low-nitrogen limit

Waele, Sam De; Lejaeghere, Kurt; Leunis, Elke; Duprez, Lode; Cottenier, Stefaan

doi:10.1016/j.jallcom.2018.09.356

Cited by 10 publications

(10 citation statements)

References 90 publications

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“…Such a special character of the thermodynamics of γ -Fe 4 N seems to be confirmed by thermodynamic data predicted in a recent work using first-principles calculations [75]. In that work, vibrational thermodynamic and magnetic properties were worked out for P = 0 GPa and T > 0 K for α-Fe, the nitrides α"-Fe 16 N 2 and γ -Fe 4 N where α"-Fe 16 N 2 is found stable against α and γ at T = 0 K. (Note that α"-Fe 16 N 2 is not considered in the present work but it is, in any case, metastable against α+ε , as implied by the data listed in Reference [76], although it was apparently not pointed out explicitly.…”

Section: Discussion Of the P-t-dependent Phase Stabilitysupporting

confidence: 76%

“…This situation changes with increasing temperature, i.e., the Gibbs energy of the reaction α α + γ changes its sign from positive to negative. Comparison of the heat capacity data provided by De Waele et al [75] indeed imply a higher heat capacity at low temperatures, and thus acquisition of higher entropy with increasing temperature for the γ phase as compared to α and α". The special vibrational behaviour of γ -Fe 4 N, which would definitely deserve more detailed attention, also explains the stabilisation of γ against α + ε as encountered experimentally.…”

Section: Discussion Of the P-t-dependent Phase Stabilitymentioning

confidence: 80%

“…A.L. thanks Stefaan Cottenier for providing the original data of Reference [ 75 ]. We thank Marcus Schwarz for assistance during multi-anvil calibration experiments and for providing calibration data of the 18/12 assembly type.…”

Section: Acknowledgmentsmentioning

confidence: 99%

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Phase Stability of Iron Nitride Fe4N at High Pressure—Pressure-Dependent Evolution of Phase Equilibria in the Fe–N System

et al. 2021

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Although the general instability of the iron nitride γ′-Fe4N with respect to other phases at high pressure is well established, the actual type of phase transitions and equilibrium conditions of their occurrence are, as of yet, poorly investigated. In the present study, samples of γ′-Fe4N and mixtures of α Fe and γ′-Fe4N powders have been heat-treated at temperatures between 250 and 1000 °C and pressures between 2 and 8 GPa in a multi-anvil press, in order to investigate phase equilibria involving the γ′ phase. Samples heat-treated at high-pressure conditions, were quenched, subsequently decompressed, and then analysed ex situ. Microstructure analysis is used to derive implications on the phase transformations during the heat treatments. Further, it is confirmed that the Fe–N phases in the target composition range are quenchable. Thus, phase proportions and chemical composition of the phases, determined from ex situ X-ray diffraction data, allowed conclusions about the phase equilibria at high-pressure conditions. Further, evidence for the low-temperature eutectoid decomposition γ′→α+ε′ is presented for the first time. From the observed equilibria, a P–T projection of the univariant equilibria in the Fe-rich portion of the Fe–N system is derived, which features a quadruple point at 5 GPa and 375 °C, above which γ′-Fe4N is thermodynamically unstable. The experimental work is supplemented by ab initio calculations in order to discuss the relative phase stability and energy landscape in the Fe–N system, from the ground state to conditions accessible in the multi-anvil experiments. It is concluded that γ′-Fe4N, which is unstable with respect to other phases at 0 K (at any pressure), has to be entropically stabilised in order to occur as stable phase system. In view of the frequently reported metastable retention of the γ′ phase during room temperature compression experiments, energetic and kinetic aspects of the polymorphic transition γ′⇌ε′ are discussed.

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Section: Discussion Of the P-t-dependent Phase Stabilitysupporting

confidence: 76%

Section: Discussion Of the P-t-dependent Phase Stabilitymentioning

confidence: 80%

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Phase Stability of Iron Nitride Fe4N at High Pressure—Pressure-Dependent Evolution of Phase Equilibria in the Fe–N System

et al. 2021

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“…Similar effects would likely be observed for nitrogen interstitials, as the divergence from a cubic crystal in super-saturated Fe-N is significant at c N = 4.4 at.% [40]. Furthermore, Fe 16 N 2 forms in Fe-N martensites at low temperatures (< 400 K) [41]. This affects the diffusivity of nitrogen in a substantial concentration range (0.05 at.% < c N < 11 at.%).…”

Section: Vacancy-free Diffusionmentioning

confidence: 53%

Nitrogen diffusion in vacancy-rich ferrite and austenite, from first principles to applications

Karimi

Auinger

2021

Acta Materialia

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“…It is worthy pointing out that a systematic evaluation of the thermodynamic properties for magnetic materials dictates accurate Gibbs free energies with significant magnetic contributions, 519 as illustrated for the Fe-N systems. 520 Thus, proper evaluation of the magnetization and magnetic ordering temperature is required.…”

Section: Case Studiesmentioning

confidence: 99%

High-throughput design of magnetic materials

Zhang

2021

Electron. Struct.

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Materials design based on density functional theory (DFT) calculations is an emergent field of great potential to accelerate the development and employment of novel materials. Magnetic materials play an essential role in green energy applications as they provide efficient ways of harvesting, converting, and utilizing energy. In this review, after a brief introduction to the major functionalities of magnetic materials, we demonstrated how the fundamental properties can be tackled via high-throughput DFT calculations, with a particular focus on the current challenges and feasible solutions. Successful case studies are summarized on several classes of magnetic materials, followed by bird-view perspectives.

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A first-principles reassessment of the Fe-N phase diagram in the low-nitrogen limit

Cited by 10 publications

References 90 publications

Phase Stability of Iron Nitride Fe4N at High Pressure—Pressure-Dependent Evolution of Phase Equilibria in the Fe–N System

Phase Stability of Iron Nitride Fe4N at High Pressure—Pressure-Dependent Evolution of Phase Equilibria in the Fe–N System

Nitrogen diffusion in vacancy-rich ferrite and austenite, from first principles to applications

High-throughput design of magnetic materials

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