# U system

> U system: 47 accepted literature values (crystal structure 18, phase transition 12, heat capacity / entropy / enthalpy 8, formation 5) and 0 calculated phase diagram(s) from ORCHID, each value with evidence class, source, page and quote.

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

47 accepted literature values from 9 paper(s) (experimental 9, model 23, unspecified 15); 0 calculated phase diagram(s). 15 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/U.json) · [CSV](https://data.orchid-project.org/systems/U.csv) · [interactive explorer](https://orchid-project.org/data-explorer/#U) · [papers (bibliography)](https://data.orchid-project.org/bibliography/pages/systems/U.html) · [Markdown](https://data.orchid-project.org/systems/U.md)

Table: Accepted values by evidence class

| Evidence class | Values |
|---|---:|
| experimental | 9 |
| model | 23 |
| unspecified | 15 |

Table: Accepted values by property group

| Property group | Values |
|---|---:|
| invariant reaction | 4 |
| phase transition | 12 |
| formation | 5 |
| heat capacity / entropy / enthalpy | 8 |
| crystal structure | 18 |

## Invariant reactions (literature)

Table: Invariant reactions reported in the literature for the U system (4)

| T (K) | Reaction / phases | Compositions (mole fraction) | Class | Source | Location | Quote |
|---:|---|---|---|---|---|---|
| 1408.15 | other: L -> γU | L: U 1; γU: U 1 | model | [1] Sheldon 1987 | Table 1, p. 2, row 11; `ORC-NFXOBZI3V2` |  |
| 1049.15 | polymorphic: γU -> βU | γU: U 1 | model | [1] Sheldon 1987 | Table 1, p. 2, row 12; `ORC-N2TQUI24RG` |  |
| 942.15 | polymorphic: βU -> αU | βU: U 1; αU: U 1 | model | [1] Sheldon 1987 | Table 1, p. 2, row 13; `ORC-SHAG3PELZD` |  |
| 916 | (β-U) -> (α-U) + (γ-U) | (β-U): U 0.987; (α-U): U 0.999; (γ-U): U 0.872 | model | [2] Berche 2011 | Table 3, p. 6, row 2; `ORC-75DBJRA2P2` |  |

## 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, U system (5)

| Phase | Compound | Value | T (K) | Class | MP DFT (kJ/mol-atom) | OQMD DFT (kJ/mol-atom) | Source | Location | Quote |
|---|---|---:|---:|---|---:|---:|---|---|---|
| U (g) |  | 533 kJ/mol-atom ± 8 | 298.15 | model |  |  | [3] Guéneau 2002; _cites Grenthe 1992_ | Table 4, p. 9, row 10; `ORC-S2656RJZMQ.32d462` |  |
| U (g) |  | 534.996 kJ/mol-atom | 298.15 | model |  |  | [3] Guéneau 2002 | Table 4, p. 9, row 9; `ORC-IY4HBZTVGD.c76b55` |  |
| α-U |  | 0 kJ/mol-atom | 298.15 | model |  |  | [4] Beneš 2014 | Table 1, p. 2, row 5; `ORC-OVE7SSWF73.4ad540` |  |
| β-U |  | 3.1661 kJ/mol-atom | 298.15 | model |  |  | [4] Beneš 2014 | Table 1, p. 2, row 7; `ORC-LYLLEBPACM.e1d66e` |  |
| γ-U |  | 9.5149 kJ/mol-atom | 298.15 | model |  |  | [4] Beneš 2014 | Table 1, p. 2, row 9; `ORC-7KBNK5YS3T.910025` |  |

## Other properties

### Phase transition (12)

Table: Phase transition, U system

| Property | Value | T (K) | Phases / composition | Class | Source | Location | Quote |
|---|---:|---:|---|---|---|---|---|
| Phase transition | 933.85 K | 933.85 | polymorphic: α→β; _alloy: U 1_ | experimental | [5] Mo 2021; _cites Rai 2009_ [doi](https://doi.org/10.1016/j.jnucmat.2008.09.012) | Table 2, p. 6, row 6; `ORC-CMQIULTTQ4` |  |
| Phase transition | 933.85 K | 933.85 | polymorphic: α→β; _alloy: U 1_ | experimental | [5] Mo 2021 | Table 2, p. 6, row 5; `ORC-GNISNLCULD` |  |
| Phase transition | 934.75 K | 934.75 | polymorphic: α→β; _alloy: U 1_ | experimental | [5] Mo 2021; _cites Rai 2009_ [doi](https://doi.org/10.1016/j.jnucmat.2008.09.012) | Table 2, p. 6, row 7; `ORC-ELEVHUSD2X` |  |
| Phase transition | 935.15 K | 935.15 | polymorphic: α→β; _alloy: U 1_ | experimental | [5] Mo 2021; _cites Rai 2009_ [doi](https://doi.org/10.1016/j.jnucmat.2008.09.012) | Table 2, p. 6, row 8; `ORC-3D6OQRFKI3` |  |
| Phase transition | 935.85 K | 935.85 | polymorphic: α→β; _alloy: U 1_ | experimental | [5] Mo 2021; _cites Rai 2009_ [doi](https://doi.org/10.1016/j.jnucmat.2008.09.012) | Table 2, p. 6, row 9; `ORC-YABRTEMI2V` |  |
| Phase transition | 937.65 K | 937.65 | polymorphic: α→β; _alloy: U 1_ | experimental | [5] Mo 2021 | Table 2, p. 6, row 1; `ORC-EB5RUA4EK4` |  |
| Phase transition | 938.05 K | 938.05 | polymorphic: α→β; _alloy: U 1_ | experimental | [5] Mo 2021 | Table 2, p. 6, row 4; `ORC-3CRPHIVNWA` |  |
| Phase transition | 939.15 K | 939.15 | polymorphic: α→β; _alloy: U 1_ | experimental | [5] Mo 2021 | Table 2, p. 6, row 2; `ORC-CVTLEFGSLT` |  |
| Phase transition | 939.85 K | 939.85 | polymorphic: α→β; _alloy: U 1_ | experimental | [5] Mo 2021 | Table 2, p. 6, row 3; `ORC-4PFRZAWKWX` |  |
| Phase transition | 941.15 K | 941.15 | α-U; _alloy: U 1_ | model | [6] Perron 2016; _cites Dinsdale 1991_ [doi](https://doi.org/10.1016/0364-5916%2891%2990030-n) | Table 1, p. 3, row 12; `ORC-GPLL632VXG` |  |
| Phase transition | 1049.15 K | 1049.15 | β-U; _alloy: U 1_ | model | [6] Perron 2016; _cites Dinsdale 1991_ [doi](https://doi.org/10.1016/0364-5916%2891%2990030-n) | Table 1, p. 3, row 13; `ORC-N6IWMYVMFX` |  |
| Phase transition | 1408.15 K | 1408.15 | γ-U; _alloy: U 1_ | model | [6] Perron 2016; _cites Dinsdale 1991_ [doi](https://doi.org/10.1016/0364-5916%2891%2990030-n) | Table 1, p. 3, row 14; `ORC-PFCSOFPJPI` |  |

### Heat capacity / entropy / enthalpy (8)

Table: Heat capacity / entropy / enthalpy, U system

| Property | Value | T (K) | Phases / composition | Class | Source | Location | Quote |
|---|---:|---:|---|---|---|---|---|
| Entropy; _printed: S0 (298 K)_ | 199.8 J/mol-atom/K | 298.15 | U (g); _alloy: U 1_ | model | [3] Guéneau 2002 | Table 4, p. 9, row 9; `ORC-IY4HBZTVGD.5bd667` |  |
| Entropy; _printed: S0 (298 K)_ | 199.8 J/mol-atom/K ± 0.1 | 298.15 | U (g); _alloy: U 1_ | model | [3] Guéneau 2002; _cites Grenthe 1992_ | Table 4, p. 9, row 10; `ORC-S2656RJZMQ.c3efaf` |  |
| Entropy; _printed: S0(298.15)_ | 50.2 J/mol-atom/K | 298.15 | α-U; _alloy: U 1_ | model | [4] Beneš 2014 | Table 1, p. 2, row 5; `ORC-OVE7SSWF73.893e50` |  |
| Entropy; _printed: S0(298.15)_ | 53.385 J/mol-atom/K | 298.15 | β-U; _alloy: U 1_ | model | [4] Beneš 2014 | Table 1, p. 2, row 7; `ORC-LYLLEBPACM.67b3f3` |  |
| Entropy; _printed: S0(298.15)_ | 59.774 J/mol-atom/K | 298.15 | γ-U; _alloy: U 1_ | model | [4] Beneš 2014 | Table 1, p. 2, row 9; `ORC-7KBNK5YS3T.5b2d55` |  |
| Heat capacity; _printed: C0p (298 K)_ | 23.69 J/mol-atom/K | 298.15 | U (g); _alloy: U 1_ | model | [3] Guéneau 2002 | Table 4, p. 9, row 9; `ORC-IY4HBZTVGD.24eed0` |  |
| Heat capacity; _printed: Cp0 (298 K)_ | 23.69 per mol-atom ± 0.04 | 298.15 | U (g); _alloy: U 1_ | model | [3] Guéneau 2002; _cites Grenthe 1992_ | Table 4, p. 9, row 10; `ORC-S2656RJZMQ.041b44` |  |
| Heat capacity; _printed: C0p (298 K)_ | 23.69 J/mol-atom/K ± 0.04 | 298.15 | U (g); _alloy: U 1_ | model | [3] Guéneau 2002; _cites Grenthe 1992_ | Table 4, p. 9, row 10; `ORC-S2656RJZMQ.8e04e9` |  |

### Crystal structure (18)

Table: Crystal structure, U system

| Property | Value | T (K) | Phases / composition | Class | Source | Location | Quote |
|---|---:|---:|---|---|---|---|---|
| Lattice a | 10.59 Å |  | βU; _alloy: U 1_ | model | [7] Moussa 2018; _cites Massalski 1990_ | Table 1, p. 3, row 2; `ORC-YWJNN2EPX3.0ba146` |  |
| Lattice a | 2.8537 Å | 298.15 | (αU); _(αU): U 1_ | unspecified | [1] Sheldon 1987 | Table 3, p. 3, row 8; `ORC-5ORGQUIIJS.557ccc` |  |
| Lattice a | 2.8537 Å | 298.15 | αU; _alloy: U 1_ | unspecified | [8] Chatain 2003; _cites David_ | Table 2, p. 3, row 6; `ORC-2WO72MP3ZM.18b681` |  |
| Lattice a | 10.759 Å | 298.15 | βU; _alloy: U 1_ | unspecified | [8] Chatain 2003; _cites David_ | Table 2, p. 3, row 7; `ORC-IGMIWLBC3Y.fd4681` |  |
| Lattice a | 3.524 Å | 298.15 | γU; _alloy: U 1_ | unspecified | [8] Chatain 2003; _cites David_ | Table 2, p. 3, row 8; `ORC-Y34BYAOUZJ` |  |
| Lattice a | 10.759 Å | 993.15 | (βU); _(βU): U 1_ | unspecified | [1] Sheldon 1987 | Table 3, p. 3, row 7; `ORC-5GSB332LSZ.e1a647` |  |
| Lattice a | 3.524 Å | 1078.15 | (γU); _(γU): U 1_ | unspecified | [1] Sheldon 1987 | Table 3, p. 3, row 6; `ORC-B7NKN5GG24` |  |
| Lattice b | 10.59 Å |  | βU; _alloy: U 1_ | model | [7] Moussa 2018; _cites Massalski 1990_ | Table 1, p. 3, row 2; `ORC-YWJNN2EPX3.88d42f` |  |
| Lattice b | 5.8695 Å | 298.15 | (αU); _(αU): U 1_ | unspecified | [1] Sheldon 1987 | Table 3, p. 3, row 8; `ORC-5ORGQUIIJS.c8ec86` |  |
| Lattice b | 5.8695 Å | 298.15 | αU; _alloy: U 1_ | unspecified | [8] Chatain 2003; _cites David_ | Table 2, p. 3, row 6; `ORC-2WO72MP3ZM.a32e51` |  |
| Lattice c | 5.634 Å |  | βU; _alloy: U 1_ | model | [7] Moussa 2018; _cites Massalski 1990_ | Table 1, p. 3, row 2; `ORC-YWJNN2EPX3.c7f6fc` |  |
| Lattice c | 4.9548 Å | 298.15 | (αU); _(αU): U 1_ | unspecified | [1] Sheldon 1987 | Table 3, p. 3, row 8; `ORC-5ORGQUIIJS.3a2289` |  |
| Lattice c | 4.9548 Å | 298.15 | αU; _alloy: U 1_ | unspecified | [8] Chatain 2003; _cites David_ | Table 2, p. 3, row 6; `ORC-2WO72MP3ZM.0b21f0` |  |
| Lattice c | 5.656 Å | 298.15 | βU; _alloy: U 1_ | unspecified | [8] Chatain 2003; _cites David_ | Table 2, p. 3, row 7; `ORC-IGMIWLBC3Y.90e439` |  |
| Lattice c | 5.656 Å | 993.15 | (βU); _(βU): U 1_ | unspecified | [1] Sheldon 1987 | Table 3, p. 3, row 7; `ORC-5GSB332LSZ.8780e8` |  |
| Molar volume; _printed: V_ | 12.65 cm^3 mol^-1 |  | B.c.c.; _alloy: U 1_ | unspecified | [9] Ogawa 1993 | Table 1, p. 2, row 2; `ORC-VOUEJVQBO3` |  |
| Molar volume; _printed: V_ | 12.65 cm^3 mol^-1 |  | F.c.c.; _alloy: U 1_ | unspecified | [9] Ogawa 1993 | Table 1, p. 2, row 3; `ORC-NC3RBKO56A` |  |
| Molar volume; _printed: V_ | 13.78 cm^3 mol^-1 |  | Liquid; _alloy: U 1_ | unspecified | [9] Ogawa 1993 | Table 1, p. 2, row 1; `ORC-ABKLGE4FGP` |  |

## Sources

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

1. R. I. Sheldon, E. M. Foltyn, D. E. Peterson, The Sn-U (Tin-Uranium) system, Bulletin of Alloy Phase Diagrams 8, 347-352 (1987). [doi:10.1007/bf02869271](https://doi.org/10.1007/bf02869271)
2. A. Berche, N. Dupin, C. Guéneau, C. Rado, B. Sundman, J.C. Dumas, Calphad thermodynamic description of some binary systems involving U, Journal of Nuclear Materials 411, 131-143 (2011). [doi:10.1016/j.jnucmat.2011.01.043](https://doi.org/10.1016/j.jnucmat.2011.01.043)
3. C. Guéneau, M. Baichi, D. Labroche, C. Chatillon, B. Sundman, Thermodynamic assessment of the uranium–oxygen system, Journal of Nuclear Materials 304, 161-175 (2002). [doi:10.1016/s0022-3115(02)00878-4](https://doi.org/10.1016/s0022-3115%2802%2900878-4)
4. O. Beneš, D. Manara, R.J.M. Konings, Thermodynamic assessment of the Th–U–Pu system, Journal of Nuclear Materials 449, 15-22 (2014). [doi:10.1016/j.jnucmat.2014.02.001](https://doi.org/10.1016/j.jnucmat.2014.02.001)
5. Chuan Mo, Wenlin Mo, Baixue Bian, Peng Zhou, Yong Du, Tao Fa et al., Experimental investigation of the U-rich region and thermodynamic re-assessment of the U–Ti system, Journal of Nuclear Materials 557, 153317 (2021). [doi:10.1016/j.jnucmat.2021.153317](https://doi.org/10.1016/j.jnucmat.2021.153317)
6. A. Perron, P.E.A. Turchi, A. Landa, B. Oudot, B. Ravat, F. Delaunay, Thermodynamic assessments and inter-relationships between systems involving Al, Am, Ga, Pu, and U, Journal of Nuclear Materials 482, 187-200 (2016). [doi:10.1016/j.jnucmat.2016.09.012](https://doi.org/10.1016/j.jnucmat.2016.09.012)
7. Chantal Moussa, Alexandre Berche, José Barbosa, Mathieu Pasturel, Bertrand Stepnik, Olivier Tougait, Experimental investigation of the phase equilibria and thermodynamic assessment in the U-Ga and U-Al-Ga systems, Journal of Nuclear Materials 499, 361-371 (2018). [doi:10.1016/j.jnucmat.2017.11.037](https://doi.org/10.1016/j.jnucmat.2017.11.037)
8. S. Chatain, C. Guéneau, D. Labroche, O. Dugne, J. Rogez, Thermodynamic assessment of the Fe-U binary system, JPE 24, 122-131 (2003). [doi:10.1361/105497103770330730](https://doi.org/10.1361/105497103770330730)
9. Toru Ogawa, Alloying behaviour among U, Np, Pu and Am predicted with the Brewer valence bond model, Journal of Alloys and Compounds 194, 1-7 (1993). [doi:10.1016/0925-8388(93)90636-2](https://doi.org/10.1016/0925-8388%2893%2990636-2)

## 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 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_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/).