# Fe–Hf system

> Fe–Hf system: 32 accepted literature values (invariant reaction 14, formation 12, phase transition 5, heat capacity / entropy / enthalpy 1) and 1 calculated phase diagram(s) from ORCHID, each value with evidence class, source, page and quote.

HTML: https://data.orchid-project.org/systems/FE-HF.html · Markdown: https://data.orchid-project.org/systems/FE-HF.md

32 accepted literature values from 1 paper(s) (experimental 13, model 19); 1 calculated phase diagram(s). 2 further extracted value(s) not accepted by the reader-agreement checks are only in the JSON/CSV.

Data: [JSON](https://data.orchid-project.org/literature/systems/FE-HF.json) · [CSV](https://data.orchid-project.org/systems/FE-HF.csv) · [interactive explorer](https://orchid-project.org/data-explorer/#FE-HF) · [interactive phase diagram](https://orchid-project.org/phase-diagrams/#FE-HF/FeHf-08Idb.json) · [phases (8)](https://data.orchid-project.org/phases/pages/FE-HF.html) · [papers (bibliography)](https://data.orchid-project.org/bibliography/pages/systems/FE-HF.html) · [Markdown](https://data.orchid-project.org/systems/FE-HF.md)

Table: Accepted values by evidence class

| Evidence class | Values |
|---|---:|
| experimental | 13 |
| model | 19 |

Table: Accepted values by property group

| Property group | Values |
|---|---:|
| invariant reaction | 14 |
| phase transition | 5 |
| formation | 12 |
| heat capacity / entropy / enthalpy | 1 |

## Calculated phase diagrams

Binary phase diagrams calculated with pycalphad 0.11.2 from the SGTE binary collection (Hallstedt 2025, CC BY 4.0). Evidence class: model.

Table: Assessments with a calculated phase diagram

| TDB file | Assessment | SHA-256 | Links |
|---|---|---|---|
| FeHf-08Idb.tdb | M. Idbenali, N. Selhaoui, L. Bouirden, C. Servant, J. Alloys Compd., 456, 151-58(2008). [doi:10.1016/j.jallcom.2007.02.036](https://doi.org/10.1016/j.jallcom.2007.02.036) | `2a85ddea9bbae84b610150905ff4dcd238fbf61cba0fab193be31db3d1d84dbd` | [viewer](https://orchid-project.org/phase-diagrams/#FE-HF/FeHf-08Idb.json) · [TDB](https://orchid-project.org/data/databases/sgte-binary/FeHf-08Idb.tdb) · [JSON](https://data.orchid-project.org/phase-diagrams/sgte/FeHf-08Idb.json) |

Table: Calculated three-phase invariants (model, mole fraction of the second component)

| TDB file | T (K) | Phases at the invariant |
|---|---:|---|
| FeHf-08Idb.tdb | 1933.37 | FE2HF_C14 (x(Hf) 0.31962) + FE2HF_C36 (x(Hf) 0.33333) + LIQUID (x(Hf) 0.4884) |
| FeHf-08Idb.tdb | 1933.37 | FE2HF_C14 (x(Hf) 0.31961) + FE2HF_C36 (x(Hf) 0.33333) + LIQUID (x(Hf) 0.48833) |
| FeHf-08Idb.tdb | 1661.09 | BCC_A2 (x(Hf) 0.0029) + LIQUID (x(Hf) 0.06067) + FE2HF_C14 (x(Hf) 0.24546) |
| FeHf-08Idb.tdb | 1607.59 | FCC_A1 (x(Hf) 1.800e-4) + BCC_A2 (x(Hf) 0.00221) + FE2HF_C14 (x(Hf) 0.24504) |
| FeHf-08Idb.tdb | 1607.59 | FCC_A1 (x(Hf) 1.800e-4) + BCC_A2 (x(Hf) 0.00221) + FE2HF_C14 (x(Hf) 0.24504) |
| FeHf-08Idb.tdb | 1573.55 | FE2HF_C36 (x(Hf) 0.33333) + LIQUID (x(Hf) 0.64718) + BCC_A2 (x(Hf) 0.87781) |
| FeHf-08Idb.tdb | 1573.55 | FE2HF_C36 (x(Hf) 0.33333) + LIQUID (x(Hf) 0.6472) + BCC_A2 (x(Hf) 0.87783) |
| FeHf-08Idb.tdb | 1531.26 | FE2HF_C36 (x(Hf) 0.33333) + FEHF2 (x(Hf) 0.66667) + BCC_A2 (x(Hf) 0.87902) |
| FeHf-08Idb.tdb | 1531.26 | FE2HF_C36 (x(Hf) 0.33333) + FEHF2 (x(Hf) 0.66667) + BCC_A2 (x(Hf) 0.879) |
| FeHf-08Idb.tdb | 1531.26 | FE2HF_C36 (x(Hf) 0.33333) + FEHF2 (x(Hf) 0.66667) + BCC_A2 (x(Hf) 0.87901) |
| FeHf-08Idb.tdb | 1508.56 | FEHF2 (x(Hf) 0.66667) + BCC_A2 (x(Hf) 0.88276) + HCP_A3 (x(Hf) 1) |
| FeHf-08Idb.tdb | 1508.56 | FEHF2 (x(Hf) 0.66667) + BCC_A2 (x(Hf) 0.88282) + HCP_A3 (x(Hf) 1) |
| FeHf-08Idb.tdb | 1508.56 | FEHF2 (x(Hf) 0.66667) + BCC_A2 (x(Hf) 0.88283) + HCP_A3 (x(Hf) 1) |
| FeHf-08Idb.tdb | 1474.54 | FE2HF_C36 (x(Hf) 0.33333) + FE2HF_C15 (x(Hf) 0.33333) + FEHF2 (x(Hf) 0.66667) |
| FeHf-08Idb.tdb | 1474.54 | FE2HF_C14 (x(Hf) 0.31727) + FE2HF_C15 (x(Hf) 0.33333) + FE2HF_C36 (x(Hf) 0.33333) |
| FeHf-08Idb.tdb | 1474.54 | FE2HF_C14 (x(Hf) 0.31727) + FE2HF_C36 (x(Hf) 0.33333) + FE2HF_C15 (x(Hf) 0.33333) |
| FeHf-08Idb.tdb | 1185.91 | FCC_A1 (x(Hf) 1.000e-5) + BCC_A2 (x(Hf) 1.100e-4) + FE2HF_C14 (x(Hf) 0.243) |
| FeHf-08Idb.tdb | 1185.91 | FCC_A1 (x(Hf) 1.000e-5) + BCC_A2 (x(Hf) 1.100e-4) + FE2HF_C14 (x(Hf) 0.243) |

Convex hulls: [Materials Project DFT hull](https://data.orchid-project.org/hulls/dft-mp/FE/FE-HF.json) · [OQMD DFT hull](https://data.orchid-project.org/hulls/dft-oqmd/FE/FE-HF.json)

## Invariant reactions (literature)

Table: Invariant reactions reported in the literature for the Fe–Hf system (14)

| T (K) | Reaction / phases | Compositions (mole fraction) | Class | Source | Location | Quote |
|---:|---|---|---|---|---|---|
| 1914.15 | Liq + λ -> βFe2Hf | Liq: Hf 0.5016; λ: Hf 0.3209 | model | [1] Idbenali 2008 | Table 4, p. 5, row 14; `ORC-FLVU3Q5RFZ` |  |
| 1913.15 | Liq + λ -> βFe2Hf | Liq: Hf 0.482; λ: Hf 0.0327 | experimental | [1] Idbenali 2008; _cites Svechnikov 1961_ | Table 4, p. 5, row 13; `ORC-TMGCFDBQMW` |  |
| 1663.15 | eutectic: Liq -> (δFe) + λ | Liq: Hf 0.079; (δFe): Hf 0.0145; λ: Hf 0.251 | experimental | [1] Idbenali 2008; _cites Svechnikov 1961_ | Table 4, p. 5, row 11; `ORC-PX5CNIW4RK` |  |
| 1662.15 | eutectic: Liq -> (δFe) + λ | Liq: Hf 0.0604; (δFe): Hf 0.00288; λ: Hf 0.2454 | model | [1] Idbenali 2008 | Table 4, p. 5, row 12; `ORC-DZXILFULF7` |  |
| 1608.15 | (γFe) -> (δFe) + λ | (γFe): Hf 0.0022; (δFe): Hf 1.800e-4; λ: Hf 0.245 | model | [1] Idbenali 2008 | Table 4, p. 5, row 10; `ORC-QNNBNFBJY7` |  |
| 1603.15 | (γFe) -> (δFe) + λ | (γFe): Hf 0.00835; (δFe): Hf 0.0051; λ: Hf 0.257 | experimental | [1] Idbenali 2008; _cites Svechnikov 1961_ | Table 4, p. 5, row 9; `ORC-I6AKBQRSUR` |  |
| 1574.15 | eutectic: Liq -> (βHf) + βFe2Hf | Liq: Hf 0.6472; (βHf): Hf 0.8788 | model | [1] Idbenali 2008 | Table 4, p. 5, row 8; `ORC-OARPXQ2EGY` |  |
| 1573.15 | eutectic: Liq -> (βHf) + βFe2Hf | Liq: Hf 0.639; (βHf): Hf 0.955 | experimental | [1] Idbenali 2008; _cites Svechnikov 1961_ | Table 4, p. 5, row 7; `ORC-6BAA5VZO2O` |  |
| 1533.15 | (βHf) + βFe2Hf -> FeHF2 | (βHf): Hf 0.964 | experimental | [1] Idbenali 2008; _cites Svechnikov 1961_ | Table 4, p. 5, row 5; `ORC-FHRPCPEV3R` |  |
| 1533.15 | (βHf) + βFe2Hf -> FeHF2 | (βHf): Hf 0.879 | model | [1] Idbenali 2008 | Table 4, p. 5, row 6; `ORC-YCEM5ZHRTD` |  |
| 1509.15 | (βHf) -> (αHf) + FeHF2 | (βHf): Hf 0.8828; (αHf): Hf 1 | model | [1] Idbenali 2008 | Table 4, p. 5, row 4; `ORC-4H57ZGOV4R` |  |
| 1508.15 | (βHf) -> (αHf) + FeHF2 | (βHf): Hf 0.97; (αHf): Hf 0.99 | experimental | [1] Idbenali 2008; _cites Svechnikov 1961_ | Table 4, p. 5, row 3; `ORC-GJD7GPBUGR` |  |
| 1186.15 | (αFe) -> (γFe) + λ | (αFe): Hf 1.060e-4; (γFe): Hf 1.300e-5; λ: Hf 0.243 | model | [1] Idbenali 2008 | Table 4, p. 5, row 18; `ORC-Q4FAAPKGEL` |  |
| 1185.15 | (αFe) -> (γFe) + λ | (αFe): Hf 0.00196; λ: Hf 0.281 | experimental | [1] Idbenali 2008; _cites Svechnikov 1961_ | Table 4, p. 5, row 17; `ORC-EGQLXXAQN6` |  |

## Formation enthalpies

Literature values in kJ/mol-atom where the per-atom basis is known. DFT columns: the lowest-energy entry at the same composition (Materials Project 2026.04.13, OQMD v1.8; different energy references, never averaged), from [dft_parity.json](https://data.orchid-project.org/literature/dft_parity.json).

Table: Enthalpies of formation, Fe–Hf system (12)

| Phase | Compound | Value | T (K) | Class | MP DFT (kJ/mol-atom) | OQMD DFT (kJ/mol-atom) | Source | Location | Quote |
|---|---|---:|---:|---|---:|---:|---|---|---|
| Fe2Hf-HT | [Fe2Hf](https://data.orchid-project.org/compounds/Fe2Hf.html) | -40.33 kJ/mol-atom | 1723 | model | -33.396 (mp-aaaaaamv) | -33.317 (oqmd-30206) | [1] Idbenali 2008 | Table 2, p. 3, row 5; `ORC-33R32KVOQ6` |  |
| Fe2Hf-HT | [Fe2Hf](https://data.orchid-project.org/compounds/Fe2Hf.html) | -39.4 kJ/mol-atom ± 4.3 | 1723 | experimental | -33.396 (mp-aaaaaamv) | -33.317 (oqmd-30206) | [1] Idbenali 2008; _cites Gachon 1992_ [doi](https://doi.org/10.1007/bf02665763) | Table 2, p. 3, row 1; `ORC-U33KIRTKYB` |  |
| Fe2Hf-HT | [Fe2Hf](https://data.orchid-project.org/compounds/Fe2Hf.html) | -28 kJ/mol-atom | 298.15 | model | -33.396 (mp-aaaaaamv) | -33.317 (oqmd-30206) | [1] Idbenali 2008; _cites Niessen 1983_ [doi](https://doi.org/10.1016/0364-5916%2883%2990030-5) | Table 2, p. 3, row 3; `ORC-P4EXKTIHXS` |  |
| Fe2Hf-HT | [Fe2Hf](https://data.orchid-project.org/compounds/Fe2Hf.html) | -25 kJ/mol-atom |  | model | -33.396 (mp-aaaaaamv) | -33.317 (oqmd-30206) | [1] Idbenali 2008; _cites Colinet 1985_ [doi](https://doi.org/10.1016/0364-5916%2885%2990032-x) | Table 2, p. 3, row 2; `ORC-TNJW5QELWK` |  |
| Fe2Hf-HT | [Fe2Hf](https://data.orchid-project.org/compounds/Fe2Hf.html) | -12.3 kJ/mol-atom ± 1.1 | 1373 | experimental | -33.396 (mp-aaaaaamv) | -33.317 (oqmd-30206) | [1] Idbenali 2008; _cites Meschel 2006_ [doi](https://doi.org/10.1016/j.jallcom.2005.08.006) | Table 2, p. 3, row 4; `ORC-QJ56PUEUMY` |  |
| Fe2Hf-LT | [Fe2Hf](https://data.orchid-project.org/compounds/Fe2Hf.html) | -39.86 kJ/mol-atom | 1460 | model | -33.396 (mp-aaaaaamv) | -33.317 (oqmd-30206) | [1] Idbenali 2008 | Table 2, p. 3, row 7; `ORC-2635SW7ZRV` |  |
| Fe2Hf-LT | [Fe2Hf](https://data.orchid-project.org/compounds/Fe2Hf.html) | -39.847 kJ/mol-atom | 1480 | model | -33.396 (mp-aaaaaamv) | -33.317 (oqmd-30206) | [1] Idbenali 2008 | Table 2, p. 3, row 6; `ORC-PKTL5ELOYF` |  |
| Fe2Hf-LT | [Fe2Hf](https://data.orchid-project.org/compounds/Fe2Hf.html) | -34.525 kJ/mol-atom | 298.15 | model | -33.396 (mp-aaaaaamv) | -33.317 (oqmd-30206) | [1] Idbenali 2008 | Table 2, p. 3, row 8; `ORC-VV7IHGPMSC` |  |
| FeHf2 | [FeHf2](https://data.orchid-project.org/compounds/FeHf2.html) | -24 kJ/mol-atom ± 3.5 | 1493 | experimental | -17.607 (mp-aaaaaeby) | -17.862 (oqmd-18331) | [1] Idbenali 2008; _cites Gachon 1992_ [doi](https://doi.org/10.1007/bf02665763) | Table 2, p. 3, row 9; `ORC-SZSL3Q5JC4` |  |
| FeHf2 | [FeHf2](https://data.orchid-project.org/compounds/FeHf2.html) | -23.9 kJ/mol-atom | 1493 | model | -17.607 (mp-aaaaaeby) | -17.862 (oqmd-18331) | [1] Idbenali 2008 | Table 2, p. 3, row 12; `ORC-C6YLJ6N5BU` |  |
| FeHf2 | [FeHf2](https://data.orchid-project.org/compounds/FeHf2.html) | -23 kJ/mol-atom | 298.15 | model | -17.607 (mp-aaaaaeby) | -17.862 (oqmd-18331) | [1] Idbenali 2008; _cites Niessen 1983_ [doi](https://doi.org/10.1016/0364-5916%2883%2990030-5) | Table 2, p. 3, row 11; `ORC-DCOLHL4X65` |  |
| FeHf2 | [FeHf2](https://data.orchid-project.org/compounds/FeHf2.html) | -22 kJ/mol-atom |  | model | -17.607 (mp-aaaaaeby) | -17.862 (oqmd-18331) | [1] Idbenali 2008; _cites Yu 1973_ | Table 2, p. 3, row 10; `ORC-P2Z2XXT6AU` |  |

## Other properties

### Phase transition (5)

Table: Phase transition, Fe–Hf system

| Property | Value | T (K) | Phases / composition | Class | Source | Location | Quote |
|---|---:|---:|---|---|---|---|---|
| Phase transition | 1473 K | 1473 | Fe2Hf LT + Fe2Hf HT | model | [1] Idbenali 2008; _cites Okamoto 2000_ | p. 1; `ORC-W2XX4IJVLR` | “According to the evaluation by Okamoto \[4\], the stoichiometric Fe2 Hf phase presents a crystalline transition at 1473 K from C15 (noted as ␣Fe2 Hf or Fe2 Hf cub or Fe2 Hf LT (low temperature), Cu2 Mg type) to C36 type (␤Fe2 Hf or Fe2 Hf hex2 or Fe2 Hf HT (high temperature), Ni2 Mg type).” |
| Phase transition | 1473.15 K | 1473.15 | Fe2Hf-LT -> Fe2Hf-HT; _Fe2Hf-LT: Hf 0.3333_ | experimental | [1] Idbenali 2008; _cites Svechnikov 1961_ | Table 4, p. 5, row 1; `ORC-NTG4DX7LBA` |  |
| Phase transition | 1473.15 K | 1473.15 | Fe2Hf-LT -> Fe2Hf-HT; _Fe2Hf-LT: Hf 0.3333_ | model | [1] Idbenali 2008 | Table 4, p. 5, row 2; `ORC-Y66VLDRW44` |  |
| Phase transition | 2093.15 K | 2093.15 | (Liq -> λ; _Liq: Hf 0.298_ | experimental | [1] Idbenali 2008; _cites Svechnikov 1961_ | Table 4, p. 5, row 15; `ORC-JZ4QETKMLT` |  |
| Phase transition | 2094.15 K | 2094.15 | (Liq -> λ; _Liq: Hf 0.3_ | model | [1] Idbenali 2008 | Table 4, p. 5, row 16; `ORC-F5BHTO36OM` |  |

### Heat capacity / entropy / enthalpy (1)

Table: Heat capacity / entropy / enthalpy, Fe–Hf system

| Property | Value | T (K) | Phases / composition | Class | Source | Location | Quote |
|---|---:|---:|---|---|---|---|---|
| Heat capacity; _printed: cp_ | 56 J mol-1 K-1 | 650 |  | experimental | [1] Idbenali 2008; _cites Ivanovic 1995_ [doi](https://doi.org/10.1007/bf00349909) | p. 1; `ORC-NTVMJHCVAW` | “Its specific heat has been determined in the 300-800 K temperature range by \[16\]. It first increases from 78 to 88 J mol-1 K-1 , then a pronounced drop starts around 470 K up to about 650 K (cp = 56 J mol-1 K-1 ), then the specific heat increases again from 700 K.” |

## Sources

Reporting papers the values were read from (a value cited from another work names that work in its row).

1. M. Idbenali, N. Selhaoui, L. Bouirden, C. Servant, Thermodynamic assessment of the Fe–Hf binary system, Journal of Alloys and Compounds 456, 151-158 (2008). [doi:10.1016/j.jallcom.2007.02.036](https://doi.org/10.1016/j.jallcom.2007.02.036)

## Please cite

- R. Arróyave, J. Saal, D. Shin, ORCHID-Values: thermodynamic and phase-equilibrium values read from the literature (version 2026.10; Version 1, machine-extracted), Zenodo (2026). https://doi.org/10.5281/zenodo.23735569
- R. Arróyave, J. Saal, D. Shin, ORCHID-Diagrams: calculated binary phase diagrams (version 2026.10), Zenodo (2026). https://doi.org/10.5281/zenodo.23735859
- R. Arróyave, J. Saal, D. Shin, ORCHID-Hulls: binary convex hulls (Materials Project, OQMD, assessed CALPHAD) (version 2026.10), Zenodo (2026). https://doi.org/10.5281/zenodo.23735891
- R. Arróyave, J. Saal, D. Shin, ORCHID data: umbrella record of the ORCHID datasets (version 2026.10; Version 1, machine-extracted), Zenodo (2026). https://doi.org/10.5281/zenodo.23736065

Also cite the original source of every value you use (paper_citation / paper_doi, and cited_dois for values the paper cites from earlier work); B. Hallstedt, The SGTE collection of binary datasets, Calphad 89 (2025) 102833, https://doi.org/10.1016/j.calphad.2025.102833 (CC BY 4.0), and the original assessment named in each file; A. Jain et al., The Materials Project: A materials genome approach to accelerating materials innovation, APL Materials 1 (2013) 011002, https://doi.org/10.1063/1.4812323 (CC BY 4.0); J. E. Saal et al., JOM 65 (2013) 1501, https://doi.org/10.1007/s11837-013-0755-4 and S. Kirklin et al., npj Comput. Mater. 1 (2015) 15010, https://doi.org/10.1038/npjcompumats.2015.10 (CC BY 4.0).

Version 1, machine-extracted: values were read by language-model readers constrained to quote their source and checked automatically, and the release was then audited on the printed pages by adversarial audits, an independent second review of fit-facing records and a preliminary human review of a frozen sample. Flags such as accepted and ESPEI-ready record screening results, not certification; known issues are listed in the release notes.

```bibtex
@misc{orchid_literature_2026,
  author    = {Arr{\'o}yave, Raymundo and Saal, James and Shin, Dongwon},
  title     = {{ORCHID-Values: thermodynamic and phase-equilibrium values read from the literature}},
  version   = {2026.10},
  publisher = {Zenodo},
  year      = {2026},
  doi       = {10.5281/zenodo.23735569},
  url       = {https://doi.org/10.5281/zenodo.23735569},
  note      = {Version 1, machine-extracted}
}

@misc{orchid_phase_diagrams_2026,
  author    = {Arr{\'o}yave, Raymundo and Saal, James and Shin, Dongwon},
  title     = {{ORCHID-Diagrams: calculated binary phase diagrams}},
  version   = {2026.10},
  publisher = {Zenodo},
  year      = {2026},
  doi       = {10.5281/zenodo.23735859},
  url       = {https://doi.org/10.5281/zenodo.23735859}
}

@misc{orchid_hulls_2026,
  author    = {Arr{\'o}yave, Raymundo and Saal, James and Shin, Dongwon},
  title     = {{ORCHID-Hulls: binary convex hulls (Materials Project, OQMD, assessed CALPHAD)}},
  version   = {2026.10},
  publisher = {Zenodo},
  year      = {2026},
  doi       = {10.5281/zenodo.23735891},
  url       = {https://doi.org/10.5281/zenodo.23735891}
}

@misc{orchid_data_2026,
  author    = {Arr{\'o}yave, Raymundo and Saal, James and Shin, Dongwon},
  title     = {{ORCHID data: umbrella record of the ORCHID datasets}},
  version   = {2026.10},
  publisher = {Zenodo},
  year      = {2026},
  doi       = {10.5281/zenodo.23736065},
  url       = {https://doi.org/10.5281/zenodo.23736065},
  note      = {Version 1, machine-extracted}
}
```

---

Derived data CC BY 4.0 ([licence](https://creativecommons.org/licenses/by/4.0/)): cite ORCHID ([CITATION.cff](https://data.orchid-project.org/CITATION.cff)) and the original sources. Quotes are short excerpts kept so that each value can be checked; they remain under the publishers' copyright and are not relicensed. Source papers, page images and full text are not redistributed. Field reference: [SCHEMA.md](https://data.orchid-project.org/literature/SCHEMA.md). Machine-readable guide: [llms.txt](https://data.orchid-project.org/llms.txt). Found an error? The report link of a value (Markdown: its id, ORC-..., in the Location column) opens a pre-filled GitHub issue, https://github.com/orchid-calphad/orchid-data/issues/new?template=report-value-error.yml&record_id=\<id>, carrying only the record id, source and value; [how to contribute](https://orchid-project.org/contribute/).