spore: profile
id: cerium-oxide
spore_version: 0.2
family: oxide-ceramics
name: Cerium(IV) oxide
abbreviation: CeO2
role: oxygen-storage oxide, UV-absorbing dopant and radiation-resistant cover-glass additive
category: ceramics
type: oxides
summary: |
  Cerium(IV) oxide (ceria, CeO2) is a pale-yellow oxide with a cubic fluorite crystal structure. PubChem's record, drawn from the U.S. Department of Energy PAC Chemical Database, gives a melting point of 2600 degC and a density of 7.65 g/cm3 at 25 degC. Ceria is best known as a catalyst and oxygen store, and as a dopant. NASA Langley found in 1970 and 1973 that adding about 1.5 percent ceria to solar-cell cover glass made the glass much less prone to darkening under 1 MeV electrons than undoped glass. Gadolinia-doped ceria, a related material, reached 0.104 S/cm of grain-boundary ionic conductivity at 700 degC in a 2024 study.
best_for: Radiation-resistant and UV-absorbing cover glass (NASA reports on 1.5 percent ceria-doped Micro-Sheet; SCHOTT describes a cerium-doped cover glass)
weakest_at: Hazard classification in the NITE entry (H371 and H372, lung effects from repeated exposure, signal word Danger), and no space-flight record for pure CeO2
identity:
  formula: CeO2
  cas: 1306-38-3
  crystal_system: cubic
  space_group: Fm-3m (fluorite)
  source: pmc-ceria-review-2021
  where: Introduction, cubic fluorite lattice with Fm-3m space group and oxygen on the 8c sites; CAS number and molecular formula from PubChem CID 73963
tags:
  environments: []
  stresses:
    - total-radiation-dose
    - uv
  applications:
    - solar-arrays
    - radiation-shielding
properties:
  - benchmark: melting_point
    value: 2600
    unit: °C
    scope: material
    conditions:
      basis: value in PubChem Experimental Properties, from the PAC Chemical Database (U.S. Department of Energy)
      form: CeO2 (ceria)
    method: Database value, read from the PubChem record for CID 73963
    status: ground
    source: pubchem-ceria
    where: Chemical and Physical Properties, Experimental Properties, Melting Point (reference 24)
  - benchmark: density
    value: 7.65
    unit: g/cm3
    scope: material
    conditions:
      temperature: 25 °C
      form: CeO2 (ceria)
    method: Database value, read from the PubChem record for CID 73963
    status: ground
    source: pubchem-ceria
    where: Chemical and Physical Properties, Experimental Properties, Density (reference 24)
  - benchmark: molecular_weight
    label: Molecular weight, CeO2
    value: 172.115
    unit: g/mol
    scope: material
    conditions:
      basis: computed by PubChem from the molecular formula
    method: Computed property read from the PubChem property table (REST API)
    status: calculated
    source: pubchem-mw
    where: Computed Properties, Molecular Weight
  - benchmark: ionic_conductivity
    label: Grain-boundary ionic conductivity, 15 mol % gadolinia-doped ceria
    value: 0.104
    unit: S/cm
    scope: material
    conditions:
      composition: Gd0.15Ce0.85O2-delta (15 mol % Gd3+)
      temperature: 700 °C
      atmosphere: air
      component: grain boundary
    method: Impedance spectroscopy (EIS) between 350 and 700 °C, as reported in the abstract
    status: ground
    note: Doped ceria, not pure CeO2. The abstract gives this as the highest value across the compositions tested.
    source: gdc-sci-rep-2024
    where: Abstract
  - benchmark: activation_energy
    label: Activation energy, grain-boundary ionic conduction, 15 mol % gadolinia-doped ceria
    value: 0.81
    unit: eV
    scope: material
    conditions:
      composition: Gd0.15Ce0.85O2-delta (15 mol % Gd3+)
      component: grain boundary
    method: Arrhenius fit of the impedance data, as reported in the abstract
    status: ground
    source: gdc-sci-rep-2024
    where: Abstract
  - benchmark: density_relative_to_theoretical
    label: Relative density of gadolinia-doped ceria pellets
    value: 98
    unit: '% of theoretical'
    scope: material
    conditions:
      composition: Gd_x Ce_(1-x) O2-delta (0 to 20 mol % Gd), co-precipitated nanoparticles
    method: Field-emission SEM observation, as reported in the abstract (around 98 percent)
    status: ground
    source: gdc-sci-rep-2024
    where: Abstract
  - benchmark: transmittance
    label: Transmittance of a cerium-doped solar cell cover glass
    value: 92
    bound: lower
    unit: '%'
    scope: material
    conditions:
      product: SCHOTT cerium-doped solar cell cover glass (glass, not pure CeO2)
      spectral_range: UV-A to near-infrared
    method: Manufacturer statement on its product page
    status: ground
    note: A manufacturer claim. The page gives no test method or sample thickness.
    source: schott-ceria-glass
    where: Product description, first section on the cerium-doped cover glass
  - benchmark: dopant_level
    label: Ceria dopant level in the 1973 test glass
    value: 1.5
    unit: '% by weight'
    scope: material
    conditions:
      host: Micro-Sheet solar-cell cover glass
      addition: ceria added during the melting process
    method: Composition of the test glass as stated by the authors
    status: ground
    source: nasa-tn-d7245
    where: Abstract; Introduction (ceria doping to a level of 1.5 percent made part of the melting process)
  - benchmark: dopant_level
    label: Optimum ceria dopant level, cover glass
    value: 1
    value_high: 2
    bound: range
    unit: '% by weight'
    scope: material
    conditions:
      host: solar-cell cover glass (frequently used Micro-Sheet type)
      irradiation: 1 MeV electrons to 5 x 10^14 e/cm2 and 22 MeV protons to 10^13 p/cm2
    method: Range stated as optimum by the authors of the 1970 NASA note
    status: ground
    source: nasa-tn-1971
    where: Summary
  - benchmark: wideband_transmission_loss
    label: Wideband transmission loss after 1 MeV electrons, undoped cover glass, single-coated
    value: 3.85
    unit: '%'
    scope: material
    conditions:
      glass: undoped solar-cell cover glass, single-coated (antireflection only)
      reference: undoped glass used for comparison with the ceria glass
    method: Wideband transmission measured before and after electron irradiation
    status: ground
    note: Reference value for undoped glass, not a ceria value. The 1.5 percent ceria glass lost much less (the report calls the loss very small without printing a figure in the text read).
    source: nasa-tn-d7245
    where: Results, text on undoped glass and Table II
  - benchmark: wideband_transmission_loss
    label: Wideband transmission loss after 1 MeV electrons, undoped cover glass, double-coated
    value: 3.6
    unit: '%'
    scope: material
    conditions:
      glass: undoped solar-cell cover glass, double-coated (antireflection and UV reflection)
      reference: undoped glass used for comparison with the ceria glass
    method: Wideband transmission measured before and after electron irradiation
    status: ground
    note: Reference value for undoped glass, not a ceria value.
    source: nasa-tn-d7245
    where: Results, text on undoped glass and Table II
  - benchmark: cte
    label: Linear coefficient of thermal expansion, experimental
    value: 11.6
    unit: ppm/K
    scope: material
    conditions:
      basis: experimental value quoted by an arXiv paper for CeO2; temperature range not stated in the text read
      unit_in_source: 1.16 x 10^-5 K^-1
    method: Quoted by the paper as the experimental value, set against its own simulated value (1.05 x 10^-5 K^-1). Converted from 1.16 x 10^-5 K^-1 to 11.6 ppm/K.
    status: ground
    source: arxiv-han-2023
    where: Discussion of Fig. 1 (lattice constants against temperature), sentence on the linear thermal expansion coefficient of CeO2
corrosion:
  - environment: Electron radiation at space-representative energies (laboratory, 1 MeV electrons)
    headline: Ceria doping greatly reduces the radiation darkening that undoped cover glass shows.
    effect: Undoped Micro-Sheet cover glass browned under 1 MeV electrons and lost 3.85 percent (single-coated) and 3.60 percent (double-coated) of wideband transmission. The 1.5 percent ceria-doped glass lost very little by comparison, and the authors found that a 5.0 percent ceria glass gave no significant further gain at the thickness tested.
    rating: low
    conditions:
      exposure: 1 MeV electron irradiation in the laboratory
      material: 1.5 percent ceria Micro-Sheet cover glass
      note: ceria here is a dopant inside the glass, not a CeO2 layer
    source: nasa-tn-d7245
    where: Results (Figs. 4 to 8, Table II)
  - environment: Ultraviolet exposure of a glass cover (doped ceria)
    headline: Dopants added to ceria are reported to raise its chemical stability and UV absorption.
    effect: The review says that adding dopants to ceria can enrich its thermal and chemical stability and give strong ultraviolet absorption. It gives no exposure time or dose, so the statement is qualitative.
    rating: low
    conditions:
      basis: general review statement on doped ceria, no exposure test
    source: pmc-ceria-review-2021
    where: Introduction to the section on ceria doping
  - environment: Water and humid air
    headline: CeO2 is insoluble in water. No humidity or corrosion test on ceria was found.
    effect: The Merck Index entry reproduced in PubChem describes CeO2 as white (pure) to pale-yellow crystals that are insoluble in water. No humidity exposure or corrosion test on ceria was read, so the rating reflects solubility only.
    rating: low
    conditions:
      basis: qualitative solubility statement
      exposure: not tested in the sources read
    source: pubchem-ceria
    where: Experimental Properties, Physical Description (Merck Index)
  - environment: Hydrogen at high temperature (reducing gas)
    headline: Hydrogen reduces CeO2 powder at high temperature, forming nonstoichiometric ceria.
    effect: The review reports hydrogen as a reducing agent for CeO2 powders at high temperature and at atmospheric pressure. Nonstoichiometric ceria (CeO2-y) then stores oxygen. The passage read gives no temperature, rate or reversal behaviour for this reaction.
    rating: low
    conditions:
      basis: literature statement in the review, no test conditions given
    source: pmc-ceria-review-2021
    where: Section on oxygen storage and hydrogen reduction of CeO2 (passage on H2 as a reducing agent)
risks:
  hazards:
    - text: PubChem's aggregated ECHA record gives 565 of 651 company reports as not meeting GHS hazard criteria. The remaining 86 reports carry hazard statement codes.
      ghs: []
      source: pubchem-ghs
      where: Safety and Hazards, GHS Classification, ECHA C and L notifications summary (reference 16)
    - text: The NITE-CMC classification in PubChem gives the signal word Danger and lists H371 (may cause damage to organs, specific target organ toxicity, single exposure) and H372 (causes damage to organs through prolonged or repeated exposure). Both are linked to the lung, with Category 1 for repeated exposure.
      ghs:
        - H371
        - H372
      source: pubchem-ghs
      where: Safety and Hazards, GHS Classification, NITE-CMC notification (reference 22); Hazard Classes and Categories
  failure_risks:
    - mode: Lung damage from repeated inhalation of dust
      trigger: Repeated or prolonged inhalation of airborne ceria dust in handling
      consequence: The NITE classification lists H372 (Category 1, lung) and H371 (Category 2, lung), with signal word Danger. The effect is a health hazard for people, not a failure of the material in service.
      severity: high
      source: pubchem-ghs
      where: Safety and Hazards, GHS Classification (NITE-CMC notification, reference 22)
    - mode: Radiation darkening of undoped cover glass
      trigger: 1 MeV electron irradiation of undoped solar-cell cover glass
      consequence: Undoped glass browns and loses 3.85 percent (single-coated) to 3.60 percent (double-coated) of wideband transmission. The authors say this loss would need to be designed out by overdesigning the solar array.
      severity: moderate
      source: nasa-tn-d7245
      where: Results, text on undoped glass and Table II
    - mode: Loss of oxygen to nonstoichiometric ceria
      trigger: Reducing gas such as hydrogen at high temperature
      consequence: CeO2 gives up oxygen and forms CeO2-y with oxygen vacancies. This changes the redox and ion-transport behaviour that the material is used for in catalysts and electrolytes.
      severity: low
      source: pmc-ceria-review-2021
      where: Section on oxygen storage and hydrogen reduction of CeO2
  side_effects: []
  handling:
    - text: PubChem lists the precautionary codes P260, P264, P270, P308+P316, P319, P405 and P501 for the NITE classification. The record gives the codes only, not the full wording.
      source: pubchem-ghs
      where: Safety and Hazards, GHS Classification, Precautionary Statement Codes (NITE-CMC notification)
  mitigations:
    - text: Dope the cover glass with ceria at 1 to 2 percent by weight. The 1970 NASA note calls this the optimum range, and the 1973 note found that 5.0 percent gave no significant further gain.
      source: nasa-tn-1971
      where: Summary
uses:
  - application: solar-arrays
    device: Solar-cell cover glass made from ceria-doped Micro-Sheet (NASA ground study of radiation effects)
    example: NASA Langley reported that 1.5 percent ceria-doped cover glass is much less sensitive to radiation-induced discoloration than undoped cover glass, and that it is comparable to synthetic fused silica for many space missions.
    source: nasa-tn-d7245
    where: Abstract
  - application: solar-arrays
    device: Commercial cerium-doped solar cell cover glass (SCHOTT)
    example: SCHOTT describes a new cerium-doped solar cell cover glass with over 92 percent transmittance in the UV-A to near-infrared range, proven UV protection, reduced solarization and support for long-term stability in orbit.
    source: schott-ceria-glass
    where: Product description, first section on the cerium-doped cover glass
supply:
  - subject: Cerium (rare earths group, USGS 2025 mine production, rare-earth oxide equivalent)
    abundance: Not read in a source opened for this profile
    producers:
      - country: China
        share_percent: 69.2
        year: 2025
      - country: United States
        share_percent: 13.1
        year: 2025
      - country: Australia
        share_percent: 7.4
        year: 2025
      - country: Burma
        share_percent: 5.6
        year: 2025
      - country: Thailand
        share_percent: 1.2
        year: 2025
    critical_lists:
      - list: USGS 2025 List of Critical Minerals (Cerium is listed by name)
        listed: true
      - list: EU critical raw materials list
        listed: false
    price: 'USGS: cerium oxide, 99.5% minimum, average price $1.71 per kg in 2025e (rare-earth compounds)'
    import_reliance: 'USGS: net import reliance for rare-earth compounds and metals was 67 percent of apparent consumption in 2025e'
    recycling: 'USGS: limited quantities of rare earths were recovered from batteries, permanent magnets and fluorescent lamps. The chapter does not single out cerium oxide.'
    substitutes:
      - 'USGS: substitutes are available for many rare-earth applications but generally are less effective.'
    source: usgs-mcs2026-rare-earths
    where: 'Domestic Production and Use; Salient Statistics (price and net import reliance); World Mine Production and Reserves, 2025 column (world total 390,000 t REO, rounded). Shares are calculated by Space Mushroom from the printed tonnes and the rounded world total, and cover all rare earths, not cerium alone. Critical list: USGS 2025 List of Critical Minerals page.'
media: []
documents:
  - title: 'PubChem: Ceria (CID 73963), Experimental Properties (melting point, density, physical description)'
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/73963/JSON?heading=Experimental+Properties
    year: 2026
  - title: 'PubChem: Ceria (CID 73963), GHS classification and precautionary codes'
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/73963/JSON
    year: 2026
  - title: 'USGS Mineral Commodity Summaries 2026: Rare Earths'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-rare-earths.pdf
    year: 2026
  - title: 'NASA TN D-7245: Effect of 1 MeV Electrons on Ceria-Doped Solar Cell Cover Glass'
    type: report
    url: https://ntrs.nasa.gov/api/citations/19730015355/downloads/19730015355.pdf
    year: 1973
  - title: 'NASA Technical Note (Langley, Dec 1970): Effect of Radiation on Cerium-Doped Solar-Cell Cover Glass'
    type: report
    url: https://ntrs.nasa.gov/api/citations/19710002803/downloads/19710002803.pdf
    year: 1970
  - title: Gd-doped ceria with extraordinary oxygen-ion conductivity for low temperature solid oxide fuel cells (open access)
    type: paper
    url: https://www.nature.com/articles/s41598-024-59030-6
    year: 2024
  - title: An Insight into Geometries and Catalytic Applications of CeO2 from a DFT Outlook (Molecules 26, 6485, open access)
    type: paper
    url: https://pmc.ncbi.nlm.nih.gov/articles/PMC8588098/
    year: 2021
  - title: 'SCHOTT: Solar cell cover glass, cerium-doped generation'
    type: datasheet
    url: https://www.schott.com/en-cz/solar-cell-cover-glass
    year: 2026
  - title: Predictions and Measurements of Thermal Conductivity of Ceramic Materials at High Temperature (arXiv:2305.10918)
    type: paper
    url: https://arxiv.org/pdf/2305.10918
    year: 2023
  - title: 'USGS: About the 2025 List of Critical Minerals (final list of 60 minerals)'
    type: report
    url: https://www.usgs.gov/programs/mineral-resources-program/science/about-2025-list-critical-minerals
    year: 2025
gaps:
  - No vacuum, radiation-flight or thermal-vacuum result for pure CeO2 was found. The space evidence is for ceria as a dopant in cover glass (1970 and 1973 NASA ground tests) and for a commercial glass (SCHOTT claim).
  - Atomic weights for cerium and oxygen were not read in a source opened for this profile, so the recipe parts carry no atomic_weight. The molecular weight 172.115 g/mol is PubChem's.
  - Density and melting point differ between sources. This profile uses the PubChem values (7.65 g/cm3 at 25 degC, 2600 degC). Other listings seen in search results were not read in a primary source and are not used.
  - Lattice constant of CeO2 was not read in a source opened for this profile.
  - Thermal conductivity of pure CeO2 was not found in a source read. The arXiv paper gives a simulated and experimental expansion coefficient but no conductivity for pure CeO2.
  - Ionic conductivity values for pure CeO2 were not found. The 0.104 S/cm value is for 15 mol % gadolinia-doped ceria at 700 degC, grain-boundary component.
  - Abundance of cerium in the Earth's crust was not read in a source opened for this profile.
  - The EU critical raw materials list was not checked for cerium.
  - The SCHOTT page gives no UV cut-off wavelength or luminous transmittance value. The 92 percent figure is a spectral range claim for the glass, not a pure-CeO2 value.
  - The NASA 1973 text does not print a clear number for the transmission loss of the 1.5 percent ceria glass (the table is garbled in the scan), so only the undoped-glass losses are given as values.
  - No supplier safety data sheet was read for this profile. Hazard data rest on PubChem (NITE and ECHA aggregated records). Supplier SDS documents found in search results disagree on classification and were not used.
  - Several property names are not in the canonical list (molecular_weight, ionic_conductivity, activation_energy, density_relative_to_theoretical, transmittance, dopant_level, wideband_transmission_loss). They use short snake_case names as the brief allows.
sources:
  pubchem-ceria:
    title: 'PubChem compound record, Ceria (CID 73963): Experimental Properties (melting point, density, physical description)'
    id: CID 73963; CAS 1306-38-3
    url: https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/73963/JSON?heading=Experimental+Properties
    year: 2026
    kind: database
    license: public domain (NCBI)
  pubchem-mw:
    title: 'PubChem compound record, Ceria (CID 73963): Molecular Weight (computed property)'
    id: CID 73963
    url: https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/73963/JSON?heading=Molecular+Weight
    year: 2026
    kind: database
    license: public domain (NCBI)
  pubchem-ghs:
    title: 'PubChem compound record, Ceria (CID 73963): GHS Classification (NITE-CMC and ECHA notifications, precautionary codes)'
    id: CID 73963
    url: https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/73963/JSON
    year: 2026
    kind: database
    license: public domain (NCBI)
  usgs-mcs2026-rare-earths:
    title: Mineral Commodity Summaries 2026, Rare Earths
    id: USGS MCS 2026, February 2026
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-rare-earths.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
  usgs-crit2025:
    title: About the 2025 List of Critical Minerals (USGS, final list of 60 minerals)
    id: Final 2025 List of Critical Minerals, November 2025
    url: https://www.usgs.gov/programs/mineral-resources-program/science/about-2025-list-critical-minerals
    year: 2025
    kind: web
    license: public domain (USGS)
  nasa-tn-d7245:
    title: Effect of 1 MeV Electrons on Ceria-Doped Solar Cell Cover Glass (NASA TN D-7245, Langley)
    id: NTRS 19730015355
    url: https://ntrs.nasa.gov/api/citations/19730015355/downloads/19730015355.pdf
    year: 1973
    kind: report
    license: public domain (NASA)
  nasa-tn-1971:
    title: Effect of Radiation on Cerium-Doped Solar-Cell Cover Glass (NASA Langley technical note, Dec 1970)
    id: NTRS 19710002803
    url: https://ntrs.nasa.gov/api/citations/19710002803/downloads/19710002803.pdf
    year: 1970
    kind: report
    license: public domain (NASA)
  gdc-sci-rep-2024:
    title: Gd-doped ceria with extraordinary oxygen-ion conductivity for low temperature solid oxide fuel cells
    id: doi:10.1038/s41598-024-59030-6 (Scientific Reports, 2024)
    url: https://www.nature.com/articles/s41598-024-59030-6
    year: 2024
    kind: paper
    license: open access (per publisher)
  pmc-ceria-review-2021:
    title: An Insight into Geometries and Catalytic Applications of CeO2 from a DFT Outlook
    id: doi:10.3390/molecules26216485 (Molecules 26, 6485, PMC8588098)
    url: https://pmc.ncbi.nlm.nih.gov/articles/PMC8588098/
    year: 2021
    kind: paper
    license: CC BY 4.0
  schott-ceria-glass:
    title: 'SCHOTT: Solar cell cover glass (cerium-doped generation)'
    id: manufacturer product page
    url: https://www.schott.com/en-cz/solar-cell-cover-glass
    year: 2026
    kind: datasheet
    license: manufacturer web page, linked not reproduced
  arxiv-han-2023:
    title: Predictions and Measurements of Thermal Conductivity of Ceramic Materials at High Temperature
    id: arXiv:2305.10918
    url: https://arxiv.org/pdf/2305.10918
    year: 2023
    kind: paper
    license: arXiv preprint (license as listed on arXiv)
license: CC-BY-4.0
updated: '2026-10-26'
review:
  status: draft
  method: assistant
  checked_values: 12
  unreachable: 0
  caveats: 2
  note: Drafted by an AI assistant on 2026-10-26 from pages opened in this run. Values are from PubChem, two NASA notes, a 2024 doped-ceria paper, a SCHOTT product page and an arXiv preprint. Pure-CeO2 thermal, optical and electrical values are not in the file.
story:
  recipe:
    line: CeO2 is cerium(IV) oxide. Each formula unit combines one cerium atom with two oxygen atoms. In air, cerium metal oxidizes to CeO2, which takes a fluorite crystal structure.
    parts:
      - name: Cerium
        symbol: Ce
        role: The metal centre. Cerium sits in the +4 state in CeO2. Switching between Ce4+ and Ce3+ lets the oxide store and release oxygen, which is the basis of its catalytic use.
      - name: Oxygen
        symbol: O
        role: Eight-coordinate cerium is surrounded by oxygen anions on the tetrahedral 8c sites of the fluorite lattice.
  risk_groups:
    - title: For people
      level: 1
      verdict: Hazard classification depends on the notifier
      lead: Most company reports to PubChem's ECHA record say CeO2 is not classified, but the NITE entry carries a lung-damage warning with the signal word Danger.
      points:
        - label: The powder
          line: PubChem's ECHA record gives 565 of 651 company reports as not meeting GHS hazard criteria. 86 reports list hazard codes.
        - label: Repeated exposure
          line: The NITE classification lists H372 (repeated exposure, lung, Category 1) and H371 (single exposure, lung, Category 2). Keep dust out of breathing zones.
        - label: Precautions
          line: The NITE entry lists precautionary codes P260, P264, P270, P308+P316, P319, P405 and P501 (codes only, without their full wording).
    - title: Radiation and cover glass
      lead: These results come from NASA ground tests of glass, not from flight.
      points:
        - label: Undoped glass
          line: Undoped cover glass browned under 1 MeV electrons and lost 3.85 percent of wideband transmission (single-coated) and 3.60 percent (double-coated).
        - label: Ceria-doped glass
          line: A 1.5 percent ceria glass lost much less, and the authors judged the loss very small. Going to 5.0 percent gave no significant further benefit at the thickness tested.
    - title: Handling and storage
      points:
        - label: Hydrogen
          line: Hydrogen reduces CeO2 powder at high temperature to nonstoichiometric ceria. The review gives no temperature or rate for this reaction.
  why: Cerium(IV) oxide is a stable, insoluble oxide that is useful because cerium can switch between two oxidation states. That switch lets ceria store and release oxygen, so it helps catalysts and it lets ceria absorb ultraviolet light when doped. NASA used it in cover glass because small amounts of ceria stop the glass from browning under electron radiation. Doped ceria also conducts oxide ions well at high temperature, which is why it is studied as a fuel-cell electrolyte.
  uses:
    - where: Solar-cell cover glass
      line: NASA Langley found in 1970 and 1973 that 1.5 percent ceria in Micro-Sheet cover glass resists radiation darkening far better than undoped glass. SCHOTT now sells a cerium-doped cover glass and claims over 92 percent transmittance across the UV-A to near-infrared range. Both are ground or manufacturer evidence, not flight results for pure CeO2.
    - where: Catalysts and catalytic converters
      line: A 2021 review describes ceria, alone or with noble metals, as the oxygen store in three-way catalytic converters. It converts CO and hydrocarbons to CO2 and H2O and NOx to N2. The review also reports CeO2 catalysts for CO2 conversion and VOC removal.
    - where: Solid oxide fuel cell electrolytes
      line: Gadolinia-doped ceria is studied as an electrolyte for intermediate and low temperature solid oxide fuel cells. A 2024 study reports grain-boundary ionic conductivity of 0.104 S/cm at 700 degC for the 15 mol percent Gd composition, with an activation energy of 0.81 eV.
  can_do:
    - label: Radiation tolerance
      value: 1.5 percent ceria
      line: Doping cover glass with about 1.5 percent ceria keeps the glass clear under electron radiation. The authors said the ceria glass was comparable to synthetic fused silica for many space missions.
    - label: UV absorption
      value: Over 92 percent transmittance, UV-A to NIR
      line: SCHOTT's cerium-doped cover glass is designed to protect against UV while passing the rest of the spectrum. The figure is a manufacturer claim for the glass, not pure CeO2.
    - label: Melting point
      value: 2600 degC
      line: The PubChem record gives a melting point of 2600 degC, which puts ceria well above the working range of any polymer or metal in the collection.
  compare: CeO2 is a dense, high-melting oxide with fluorite structure. Its melting point and density are printed in PubChem as 2600 degC and 7.65 g/cm3. Its expansion coefficient is about 11.6 ppm/K, close to other oxides in the ceramic group. Its main space case is as a dopant that protects glass from radiation darkening, not as a structural or thermal material.
  compare_rows:
    - label: Density
      benchmark: density
    - label: Melting point
      benchmark: melting_point
    - label: Thermal expansion
      benchmark: cte
  handling:
    - PubChem's NITE entry carries H371 and H372 and the signal word Danger. Avoid repeated inhalation of dust.
    - Hydrogen reduces CeO2 to nonstoichiometric ceria at high temperature. Keep reducing gases away from hot ceria if the oxide composition matters.
  good_for:
    - Radiation-resistant cover glass. NASA's 1970 and 1973 tests found ceria-doped glass much less prone to browning under electron radiation than undoped glass.
    - Oxygen storage in catalysts. The 2021 review describes ceria as the oxygen store in three-way catalytic converters.
  watch_out:
    - Repeated inhalation of dust. PubChem's NITE classification lists H372 (Category 1, lung) with the signal word Danger.
    - Most of the space evidence is for ceria as a dopant in glass. No flight result for pure CeO2 was found.
    - The electrolyte figures are for gadolinia-doped ceria, not pure CeO2.
  verdict: CeO2 earns its place in space work as a dopant that protects cover glass from radiation darkening. As a pure oxide it has useful melting point and density data, but the hazard entry for dust and the lack of pure-material flight data mean it should be treated as a proven dopant, not a stand-alone structural material.