U3O8
triuranium octoxide · uranium oxide, yellowcake
U3O8 is a stable, semimetallic uranium oxide that acts as the primary industrial and commercial form for uranium storage and fuel fabrication.
About triuranium octoxide
Triuranium octoxide is a robust, thermodynamically stable oxide of uranium that exists on the convex hull of stability. Its near-zero-gap electronic character distinguishes it as a semimetallic material, reflecting the complex interplay of its uranium oxidation states. This compound is the most stable form of uranium oxide under standard atmospheric conditions. It serves as the standard chemical form for the storage and transport of uranium, acting as a crucial intermediary in the production of nuclear reactor fuel. Its structural versatility is evidenced by the numerous distinct phases documented across materials databases.
Key Properties
Cross-validated computational properties for triuranium octoxide, aggregated across 3 databases.
Band GapEnergy needed to move an electron from the valence band to the conduction band. Lower or zero values tend to behave more metallic; larger gaps are more insulating or semiconducting.
Energy Above HullThermodynamic distance from the most stable set of competing phases. 0 eV/atom is on the convex hull; small positive values may still be experimentally accessible.
StabilityA plain-language summary of the best reported energy-above-hull result. It reflects whether the lowest-energy structure is on, near, or far from the stability hull.
StructuresCount of reported calculated crystal structures for this formula, including alternate polymorphs, source databases, and observed space groups.
Cross-Source DFT Agreement
How well independent DFT databases agree on the thermodynamics of U3O8. Tight agreement means computed properties can be trusted without re-running calculations.
Agreement ScoreA normalized confidence score summarizing how closely independent DFT databases agree. Higher scores mean tighter cross-source agreement.
Hull SpreadDifference between the highest and lowest energy-above-hull values reported by comparable sources. Smaller spread means less thermodynamic disagreement.
Sources ComparedNumber and names of computational sources with comparable entries for this formula.
Space Group ConsensusWhether independent sources predict the same crystal symmetry for the lowest-energy structure.
Reported Structures
Lowest-energy structures reported for U3O8, ranked by energy above hull.
| Space GroupSymmetry classification of the crystal arrangement. The number is the international space-group index. | Crystal SystemBroad lattice family, such as cubic, tetragonal, monoclinic, or triclinic, derived from unit-cell symmetry. | Band Gap (eV)Electronic gap calculated for this specific reported structure, measured in electronvolts. | E above hull (eV/atom)Thermodynamic distance from the convex hull for this structure, normalized per atom. Lower is generally more stable. | E/atom (eV)Computed total energy normalized per atom. Use energy above hull, not this value alone, when comparing stability. | Density (g/cm³)Mass per relaxed crystal volume, reported in grams per cubic centimeter. |
|---|---|---|---|---|---|
| — | — | 2.34 | 0.0000 | -3.349 | — |
| Cmcm (No. 63) | orthorhombic | 0.53 | 0.0000 | -10.388 | 8.32 |
| P-62m (No. 189) | hexagonal | 0.07 | 0.0000 | -3.431 | — |
| P-62m (No. 189) | hexagonal | 0.07 | 0.0000 | -3.431 | — |
| P-62m (No. 189) | hexagonal | 0.07 | 0.0000 | -3.431 | — |
| P-62m (No. 189) | hexagonal | 0.07 | 0.0000 | -3.431 | — |
| P-62m (No. 189) | hexagonal | 0.00 | 0.0029 | -10.385 | 8.47 |
| Cmcm (No. 63) | orthorhombic | 0.00 | 0.0031 | -10.385 | 8.35 |
| Cmmm (No. 65) | orthorhombic | 0.00 | 0.0031 | -10.385 | 8.35 |
| Amm2 (No. 38) | orthorhombic | 0.06 | 0.0034 | -10.384 | 8.29 |
| Cmcm (No. 63) | orthorhombic | 0.00 | 0.0045 | -3.426 | — |
| P-62m (No. 189) | hexagonal | 0.04 | 0.0259 | -3.405 | — |
Applications
Where triuranium octoxide is used.
Patent Landscape
4 patents reference U3O8 or close compositional variants.
| Patent | Title | Assignee | Granted |
|---|---|---|---|
| 10106409 | Method for activating U3O8 with a view to converting same into hydrated UO4 | — | — |
| 8388895 | Apparatus for producing U3O8 powder | — | — |
| 8628733 | Method for preparing uranium concentrates by fluidized bed precipitation, and preparation of UO3 and U3O8 by d | — | — |
| 9045350 | Method for converting UO3 or U3O8 into hydrated UO4 | — | — |
Frequently Asked Questions
Common questions about triuranium octoxide, answered from cross-validated data.
What is U3O8?
U3O8 is a stable, semimetallic uranium oxide that acts as the primary industrial and commercial form for uranium storage and fuel fabrication.
What is U3O8 used for?
What is the band gap of U3O8?
Is U3O8 a metal, semiconductor, or insulator?
Is U3O8 thermodynamically stable?
What is the crystal structure of U3O8?
What is the density of U3O8?
How many polymorphs of U3O8 are known?
What elements does U3O8 contain?
Where does the data for U3O8 come from?
How It Compares
As a foundational oxide in the uranium-oxygen system, U3O8 represents the most stable equilibrium phase, serving as the benchmark against which other uranium oxides are evaluated for their structural and thermodynamic properties.
Data sources & attribution
- oqmd — Data from the OQMD (oqmd.org). Cite: Saal et al., JOM 65, 1501 (2013); Kirklin et al., npj Comp. Mater. 1, 15010 (2015). (CC-BY-4.0)
- materials_project — Data from the Materials Project (materialsproject.org). Cite: Jain et al., APL Materials 1, 011002 (2013). (CC-BY-4.0)
- jarvis — Data from JARVIS (jarvis.nist.gov), NIST. Cite: Choudhary et al., npj Comp. Mater. 6, 173 (2020). (LicenseRef-US-Gov-PD)
- mpaloe — Data from MP-ALOE. Cite: Kuner et al., npj Comput. Mater. (2025), doi:10.1038/s41524-025-01834-9.
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