# UO2: enthalpy of formation > Enthalpy of formation of UO2: 7 literature value(s) with sources, pages and quotes and DFT values (Materials Project / OQMD), from ORCHID. HTML: https://data.orchid-project.org/compounds/UO2.html · Markdown: https://data.orchid-project.org/compounds/UO2.md 7 accepted literature formation-enthalpy value(s) (experimental 4, model 3); experimental median -361.637 kJ/mol-atom (n = 4); Materials Project -361.862 kJ/mol-atom (mp-aaaaacjl); OQMD -368.505 kJ/mol-atom (oqmd-20358). Systems: [O–U](https://data.orchid-project.org/systems/O-U.html) ## Literature values Table: Enthalpy of formation of UO2 reported in the literature (7) | Value | Phase as printed | T (K) | Class | Method | System | Source | Location | Quote | |---:|---|---:|---|---|---|---|---|---| | -361.637 kJ/mol-atom ± 0.278933 | UO2 | 298.15 | experimental | | [O–U](https://data.orchid-project.org/systems/O-U.html) | [1] Chevalier 2002; _cites Rand 1978_ | Table 10, p. 8, row 3; `ORC-RWSO6GJ6PB.39ba8c` | | | -361.637 kJ/mol-atom | UO2 | 298.15 | experimental | | [O–U](https://data.orchid-project.org/systems/O-U.html) | [1] Chevalier 2002; _cites Cordfunke 1988_ | Table 10, p. 8, row 4; `ORC-T4WJT4BQP5.4c7213` | | | -361.637 kJ/mol-atom ± 0.278933 | UO2 | 298.15 | experimental | | [O–U](https://data.orchid-project.org/systems/O-U.html) | [1] Chevalier 2002; _cites Huber 1969_ [doi](https://doi.org/10.1016/0021-9614%2869%2990046-9) | Table 10, p. 8, row 1; `ORC-XB7LFM5ZC5` | | | -361.219 kJ/mol-atom ± 0.8368 | UO2 | 298.15 | experimental | | [O–U](https://data.orchid-project.org/systems/O-U.html) | [1] Chevalier 2002; _cites Rand 1963_ | Table 10, p. 8, row 2; `ORC-R46T3CX36D` | | | -361.667 kJ/mol-atom ± 0.333 | UO2 (s) | 298.15 | model | | [O–U](https://data.orchid-project.org/systems/O-U.html) | [2] Guéneau 2002; _cites Grenthe 1992_ | Table 4, p. 9, row 2; `ORC-KGDWLXXJ7L.b8eb71` | | | -361.637 kJ/mol-atom | UO2 | 298.15 | model | | [O–U](https://data.orchid-project.org/systems/O-U.html) | [1] Chevalier 2002 | Table 10, p. 8, row 5; `ORC-E4WJ4DM2JX.eeaeb6` | | | -361.374 kJ/mol-atom | UO2 (s) | 298.15 | model | | [O–U](https://data.orchid-project.org/systems/O-U.html) | [2] Guéneau 2002 | Table 4, p. 9, row 1; `ORC-WJS56OFWF2.db26d2` | | ### Uncertainty budget Components kept separate, in the value's unit (literature [SCHEMA.md](https://data.orchid-project.org/literature/SCHEMA.md), [UNCERTAINTY_CALIBRATION.md](https://data.orchid-project.org/literature/UNCERTAINTY_CALIBRATION.md)): effective = max(sqrt(max(printed, reading, method)^2 + composition^2 + conversion^2), scatter). The method floor is the robust between-study scatter of the method class in ORCHID (calibrated) or a documented prior; printed values and printed uncertainties are unchanged. Table: Uncertainty budget of the literature values of UO2 | Value | Unit | Printed | Reading | Method (class, basis) | Composition | Scatter | Conversion | Effective | |---:|---|---:|---:|---|---:|---:|---:|---:| | -361.637 | kJ/mol-atom | 0.2789 | 1.667e-5 | 3.5 (unknown, calibrated) | | | | 3.5 | | -361.637 | kJ/mol-atom | | 1.667e-5 | 3.5 (unknown, calibrated) | | | | 3.5 | | -361.637 | kJ/mol-atom | 0.2789 | 1.667e-5 | 3.5 (unknown, calibrated) | | | | 3.5 | | -361.219 | kJ/mol-atom | 0.8368 | 1.667e-4 | 3.5 (unknown, calibrated) | | | | 3.5 | | -361.667 | kJ/mol-atom | 0.333 | 5.000e-4 | 3.9 (model_calculated, calibrated) | | | | 3.9 | | -361.637 | kJ/mol-atom | | 1.667e-5 | 3.9 (model_calculated, calibrated) | | | | 3.9 | | -361.374 | kJ/mol-atom | | 5.000e-4 | 3.9 (model_calculated, calibrated) | | | | 3.9 | ## DFT formation energies Lowest-energy entries at this composition. Materials Project and OQMD use different energy references and are never averaged. 1 eV/atom = 96.485 kJ/mol-atom. Table: DFT formation energy of UO2 | Source | Entry | kJ/mol-atom | eV/atom | Space group | E above hull (kJ/mol-atom) | E above hull (eV/atom) | Theoretical | |---|---|---:|---:|---|---:|---:|---| | Materials Project | mp-aaaaacjl | -361.862 | -3.75044 | Fm-3m | 0 | 0 | no | | OQMD | oqmd-20358 | -368.505 | -3.8193 | P21/c | 0 | 0 | no | DFT sources: A. Jain et al., Commentary: The Materials Project: A materials genome approach to accelerating materials innovation, APL Materials 1 (2013) 011002. [doi:10.1063/1.4812323](https://doi.org/10.1063/1.4812323) (CC BY 4.0); J. E. Saal et al., JOM 65 (2013) 1501-1509; S. Kirklin et al., npj Comput. Mater. 1 (2015) 15010. [doi:10.1007/s11837-013-0755-4](https://doi.org/10.1007/s11837-013-0755-4) (CC BY 4.0); ## Sources 1. P.-Y. Chevalier, E. Fischer, B. Cheynet, Progress in the thermodynamic modelling of the O–U binary system, Journal of Nuclear Materials 303, 1-28 (2002). [doi:10.1016/s0022-3115(02)00813-9](https://doi.org/10.1016/s0022-3115%2802%2900813-9) 2. 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) ## 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-Parity: DFT-vs-experiment formation-enthalpy benchmark (version 2026.10; Version 1, machine-extracted), Zenodo (2026). https://doi.org/10.5281/zenodo.23735943 - 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); 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); G. Kim, S. V. Meschel, P. Nash, W. Chen, Experimental formation enthalpies for intermetallic phases and other inorganic compounds, Scientific Data 4 (2017) 170162, https://doi.org/10.1038/sdata.2017.162; 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. 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_dft_benchmark_2026, author = {Arr{\'o}yave, Raymundo and Saal, James and Shin, Dongwon}, title = {{ORCHID-Parity: DFT-vs-experiment formation-enthalpy benchmark}}, version = {2026.10}, publisher = {Zenodo}, year = {2026}, doi = {10.5281/zenodo.23735943}, url = {https://doi.org/10.5281/zenodo.23735943}, 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=\, carrying only the record id, source and value; [how to contribute](https://orchid-project.org/contribute/).