Niobium pentoxide Nb2O5

spore: profile
id: niobium-pentoxide
spore_version: 0.2
family: oxide-ceramics
name: Niobium pentoxide
abbreviation: Nb2O5
role: high-rate lithium-ion anode oxide, with tantalum pentoxide as the dielectric and optical-film counterpart
category: ceramics
type: oxides
summary: |
  Niobium pentoxide (Nb2O5) is a white oxide that melts at about 1500 to 1521 °C, with a density of 4.6 g/cm3 (PubChem and a supplier SDS). Its orthorhombic T-phase is the form used for fast-charging lithium-ion anodes. A modified T-Nb2O5 anode, etched with polydopamine and doped with cobalt, kept 143 mAh/g at 1 A/g after 8500 cycles and gave 144.1 mAh/g at 10.0 A/g in a lithium cell. Tantalum pentoxide (Ta2O5) has the same stoichiometry with tantalum in place of niobium. It melts at 1872 °C and has a density of 8.2 g/cm3, and it is used as a dielectric in tantalum capacitors and in optical films. A 2021 study found that a 400 nm Ta2O5 film changed its refractive index by less than 1 percent after 2000 equivalent solar hours of vacuum ultraviolet, with its mean transmittance from 300 to 500 nm falling from 81 to 79.4 percent.
best_for: Fast-charging lithium-ion anodes where high rate matters more than energy per gram (modified T-Nb2O5), and UV-stable oxide optical films (Ta2O5)
weakest_at: Low electronic conductivity in pristine T-Nb2O5, which the anode paper says needed doping and coating; the powder is an irritant and no corrosion rate is given in the supplier SDS
identity:
  formula: Nb2O5
  cas: 1313-96-8
  crystal_system: orthorhombic
  source: pmc-tnb2o5-2022
  where: Introduction, first paragraph ('orthorhombic niobium pentoxide (T-Nb2O5)'); CAS number in Section 3 of the Lorad SDS (lorad-nb2o5-sds)
tags:
  stresses:
    - uv
  applications:
    - batteries
    - optics-and-cameras
    - electronics-and-chips
properties:
  - benchmark: melting_point
    label: Melting point, niobium pentoxide (PubChem experimental)
    value: 1500
    unit: °C
    scope: material
    conditions:
      grade: powder, as listed in the PubChem experimental record
    method: Experimental value listed in the PubChem record (its reference 15)
    status: ground
    source: pubchem-nb2o5
    where: Chemical and Physical Properties, Experimental Properties, Melting Point
  - benchmark: melting_point
    label: Melting point, niobium pentoxide powder (supplier SDS)
    value: 1521
    unit: °C
    scope: material
    conditions:
      grade: powder, Lorad item NB-4490
    method: Value printed in a supplier safety data sheet
    status: ground
    note: The PubChem record gives 1500 °C, so the two sources differ by about 20 °C.
    source: lorad-nb2o5-sds
    where: Section 9 (Physical and Chemical Properties), Melting Point row
  - benchmark: density
    label: Density, niobium pentoxide (PubChem experimental)
    value: 4.6
    unit: g/cm3
    scope: material
    conditions:
      temperature: 25 °C
    method: Experimental value listed in the PubChem record
    status: ground
    source: pubchem-nb2o5
    where: Chemical and Physical Properties, Experimental Properties, Density
  - benchmark: density
    label: Density, niobium pentoxide powder (supplier SDS)
    value: 4.6
    unit: g/cm3
    scope: material
    conditions:
      grade: powder, Lorad item NB-4490
    method: Value printed in a supplier safety data sheet
    status: ground
    source: lorad-nb2o5-sds
    where: Section 9 (Physical and Chemical Properties), Density row
  - benchmark: molecular_weight
    label: Molecular weight, Nb2O5
    value: 265.81
    unit: g/mol
    scope: material
    conditions:
      formula: Nb2O5
    method: Value printed in a supplier safety data sheet
    status: ground
    source: lorad-nb2o5-sds
    where: Section 9 (Physical and Chemical Properties), Molecular Weight row
  - benchmark: intercalation_potential
    label: Lithium intercalation potential range, T-Nb2O5 anode
    value: 1
    value_high: 3
    bound: range
    unit: V
    scope: material
    conditions:
      material: orthorhombic T-Nb2O5, as quoted in the anode paper
      reference_electrode: not stated in the paper
    method: Range stated in an open-access paper on fast-charging Nb2O5 anodes
    status: ground
    source: pmc-tnb2o5-2022
    where: Introduction, paragraph on the low intercalation potential of graphite, text 'intercalation potential range (1.0-3.0 V)'
  - benchmark: reversible_capacity
    label: Reversible capacity after 8500 cycles, modified T-Nb2O5 anode (PDA-Co-NbO)
    value: 143
    unit: mAh/g
    scope: material
    conditions:
      material: modified T-Nb2O5 (polydopamine-etched, cobalt-doped, chelation-coated); not pristine Nb2O5
      cell: Li/PDA-Co-NbO cell (lithium counter electrode)
      rate: 1 A/g
      cycles: 8500
    method: Galvanostatic cycling reported in the paper
    status: ground
    note: A laboratory cell result for a modified anode, not a commercial cell value.
    source: pmc-tnb2o5-2022
    where: Abstract; Results, cycling of the Li/PDA-Co-NbO cell
  - benchmark: rate_capacity
    label: Capacity at high rate, modified T-Nb2O5 anode (PDA-Co-NbO)
    value: 144.1
    unit: mAh/g
    scope: material
    conditions:
      material: modified T-Nb2O5 (polydopamine-etched, cobalt-doped, chelation-coated); not pristine Nb2O5
      cell: Li/PDA-Co-NbO cell (lithium counter electrode)
      rate: 10.0 A/g
    method: Rate test reported in the paper
    status: ground
    source: pmc-tnb2o5-2022
    where: Abstract (high-rate performance); Results, rate capability (capacities at 0.2 to 10.0 A/g)
  - benchmark: areal_capacity
    label: Areal capacity, T-Nb2O5 electrode at high mass loading
    value: 0.668
    unit: mAh/cm2
    scope: cell
    conditions:
      mass_loading: 4.5 mg/cm2
      cycles: 150
      material: modified T-Nb2O5 (PDA-Co-NbO) electrode
    method: Areal capacity reported in the paper
    status: ground
    source: pmc-tnb2o5-2022
    where: Abstract, last sentence
  - benchmark: interlayer_distance
    label: Theoretical interlayer distance, T-Nb2O5 layers
    value: 3.93
    unit: Å
    scope: material
    conditions:
      crystal: orthorhombic T-Nb2O5, layers along c
    method: Theoretical value quoted by the paper from earlier work (its reference 15)
    status: calculated
    source: pmc-tnb2o5-2022
    where: Introduction, paragraph on the 'room and pillar' structure, text 'theoretical interlayer distance of T-Nb2O5 is 3.93 Å'
  - benchmark: refractive_index
    label: Refractive index, Ta2O5 single layer, 400 nm, before vacuum UV at 500 nm
    value: 2.0914
    unit: '-'
    scope: material
    conditions:
      material: Ta2O5 single layer, electron-beam evaporated on quartz, designed thickness 400 nm
      wavelength: 500 nm
      state: before 2000 ESH of vacuum ultraviolet
    method: Fitted from spectrophotometer data by the full-spectrum inversion method, as described in the paper
    status: ground
    note: The paper prints this value with a space in the digits (2.091 4).
    source: ope-ta2o5-2021
    where: Results, paragraph beginning 'It can be seen that the refractive index increases after the irradiation'
  - benchmark: refractive_index
    label: Refractive index, Ta2O5 single layer, 400 nm, after vacuum UV at 500 nm
    value: 2.1116
    unit: '-'
    scope: material
    conditions:
      material: Ta2O5 single layer, electron-beam evaporated on quartz, designed thickness 400 nm
      wavelength: 500 nm
      state: after 2000 ESH of vacuum ultraviolet
    method: Fitted from spectrophotometer data by the full-spectrum inversion method, as described in the paper
    status: ground
    note: The paper prints this value with a space in the digits (2.111 6). The change is below 1 percent.
    source: ope-ta2o5-2021
    where: Results, paragraph beginning 'It can be seen that the refractive index increases after the irradiation'
  - benchmark: optical_transmittance
    label: Mean transmittance 300 to 500 nm, Ta2O5 film after vacuum UV
    value: 79.4
    unit: '%'
    scope: material
    conditions:
      material: Ta2O5 single layer, 400 nm, on quartz, normalised to the substrate
      range: 300 to 500 nm
      state: after 2000 ESH of vacuum ultraviolet
    method: Spectrophotometry reported in the paper
    status: ground
    note: Before irradiation the same film gave 81 percent in this range.
    source: ope-ta2o5-2021
    where: Results, paragraph beginning 'It can be seen that the mean transmittance of Ta2O5 thin film decreases' (Fig. 1b)
  - benchmark: melting_point
    label: Melting point, tantalum pentoxide (PubChem experimental)
    value: 1872
    unit: °C
    scope: material
    conditions:
      grade: powder, as listed in the PubChem experimental record
    method: Experimental value listed in the PubChem record
    status: ground
    source: pubchem-ta2o5
    where: Chemical and Physical Properties, Experimental Properties, Melting Point
  - benchmark: density
    label: Density, tantalum pentoxide (PubChem experimental)
    value: 8.2
    unit: g/cm3
    scope: material
    conditions:
      temperature: 25 °C
    method: Experimental value listed in the PubChem record
    status: ground
    source: pubchem-ta2o5
    where: Chemical and Physical Properties, Experimental Properties, Density
corrosion:
  - environment: Vacuum ultraviolet (2000 ESH) on a Ta2O5 single-layer film, the ageing test for spacecraft optics
    headline: The Ta2O5 film kept almost all of its optical behaviour after 2000 ESH of vacuum ultraviolet.
    effect: Refractive index rose by less than 1 percent at 500 nm, and mean transmittance from 300 to 500 nm fell from 81 to 79.4 percent. A UV-reflective multilayer that contained Ta2O5 went from 96.5 to 95.4 percent reflectance from 290 to 450 nm. The paper attributes the change to surface roughness and a change in the chemical state of tantalum at the surface.
    rating: low
    conditions:
      exposure: 2000 ESH of vacuum ultraviolet
      film: 400 nm Ta2O5 single layer on quartz, electron-beam evaporated
    source: ope-ta2o5-2021
    where: Abstract; Results, Fig. 1b and Fig. 3 text
  - environment: Water and strong oxidizing agents (Nb2O5 powder)
    headline: Nb2O5 is insoluble in water and is listed as incompatible with strong oxidizers, but no corrosion rate is given.
    effect: The supplier SDS lists the water solubility as insoluble and the material as stable under recommended storage conditions, with strong oxidizing agents as the incompatible class. It gives no rate of attack, so the attack rate in any medium is not known from this source.
    rating: unknown
    conditions:
      form: Nb2O5 powder, Lorad item NB-4490
    source: lorad-nb2o5-sds
    where: Section 9 (Water Solubility); Section 10 (Stability and Reactivity, Reacts with)
risks:
  hazards:
    - text: The Lorad SDS gives the signal word Warning and the statements H315 (skin irritation), H319 (serious eye irritation) and H335 (may cause respiratory irritation) for Nb2O5 powder.
      ghs:
        - H315
        - H319
        - H335
      source: lorad-nb2o5-sds
      where: Section 2 (Hazard Identification), Signal Word, Hazard Statements
    - text: PubChem reports the same three statements for 52.3 percent of 409 company reports; the other 47.7 percent report that Nb2O5 does not meet GHS hazard criteria.
      ghs:
        - H315
        - H319
        - H335
      source: pubchem-nb2o5
      where: Safety and Hazards, GHS Classification
    - text: PubChem reports that Ta2O5 does not meet GHS hazard criteria for 97.5 percent (78 of 80) of company reports; only two reports carry hazard codes.
      ghs: []
      source: pubchem-ta2o5
      where: Safety and Hazards, GHS Classification
  failure_risks:
    - mode: Dielectric damage in a tantalum capacitor from heating
      trigger: Power surge testing, which heats the capacitor slug, and high temperatures in service
      consequence: NASA's guideline says slug temperatures rising to 100 to 150 °C can damage the Ta2O5 dielectric and cause failure, and that space capacitors that dry out can fail catastrophically when power is switched on.
      severity: high
      source: nasa-ptc-2023
      where: Section 3.3 (power surge testing) and the text on capacitor construction, which describes the Ta2O5 dielectric
    - mode: Optical drift in a Ta2O5 film under vacuum ultraviolet
      trigger: 2000 ESH of vacuum ultraviolet on a 400 nm Ta2O5 film
      consequence: Transmittance from 300 to 500 nm fell by 1.6 points, and the paper attributes it to surface roughness and changes in the surface chemistry. The effect is small, but it matters in the blue and near-UV.
      severity: low
      source: ope-ta2o5-2021
      where: Results, transmittance paragraph (Fig. 1b)
  side_effects: []
  handling:
    - text: Keep the container tightly closed in a dry, well-ventilated place. Store locked up, as the Lorad SDS precautionary statements advise.
      source: lorad-nb2o5-sds
      where: Section 7 (Handling and Storage), Storage Conditions; precautionary statement P405
    - text: Avoid dust formation and avoid breathing dust. Use only outdoors or in a well-ventilated area.
      source: lorad-nb2o5-sds
      where: Section 6 (Accidental Release Measures); precautionary statements P261 and P271
    - text: Keep the powder away from strong oxidizing agents. In a fire, the SDS lists metal oxide fume as the decomposition product.
      source: lorad-nb2o5-sds
      where: Section 10 (Stability and Reactivity), Reacts with and Hazardous Decomposition Products
  mitigations:
    - text: Wear protective gloves and eye protection, as the SDS precautionary statement P280 advises, and wash the skin after handling (P264).
      source: lorad-nb2o5-sds
      where: Section 2 (Hazard Identification), Precautionary Statements
uses:
  - application: batteries
    device: Fast-charging lithium-ion anode (modified orthorhombic T-Nb2O5)
    example: A modified T-Nb2O5 anode reached 143 mAh/g at 1 A/g after 8500 cycles, and 144.1 mAh/g at 10.0 A/g, in a Li/PDA-Co-NbO cell. The paper says the same material also held 0.668 mAh/cm2 at 4.5 mg/cm2 after 150 cycles.
    source: pmc-tnb2o5-2022
    where: Abstract
  - application: optics-and-cameras
    device: Ta2O5 single-layer and ultraviolet-reflective films for optics in space (laboratory study)
    example: A 2021 study by a Chinese team tested Ta2O5 films and UV-reflective multilayers for vacuum ultraviolet resistance, written for optics on spacecraft. A single 400 nm Ta2O5 film kept its refractive index within 1 percent after 2000 ESH.
    source: ope-ta2o5-2021
    where: Abstract; Introduction (space optics)
  - application: electronics-and-chips
    device: Tantalum capacitors with a Ta2O5 dielectric (polymer and hermetic types)
    example: NASA's 2023 screening guideline for polymer tantalum capacitors used in NASA projects describes the Ta2O5 dielectric and the power surge test that can damage it.
    source: nasa-ptc-2023
    where: Capacitor construction text (Ta2O5 dielectric); Section 3.3 (power surge testing)
supply:
  - subject: Niobium (feedstock for Nb2O5)
    producers:
      - country: Brazil
        share_percent: 93
        year: 2025
      - country: Canada
        share_percent: 5
        year: 2025
    critical_lists:
      - list: USGS 2025 List of Critical Minerals
        listed: true
      - list: EU critical raw materials list (Regulation (EU) 2024/1252, as shown on the European Commission page)
        listed: true
    recycling: 'USGS niobium chapter: niobium was recycled with niobium-bearing steels and superalloys, but recovery specifically for niobium content was negligible; recycling may have been as much as 20 percent of apparent consumption.'
    substitutes:
      - 'USGS niobium chapter: tantalum, molybdenum and tungsten can substitute for niobium in some alloys, with a performance loss or higher cost. The chapter does not discuss Nb2O5 substitutes.'
    source: usgs-mcs2026-niobium
    where: 'Events, Trends, and Issues: ''Brazil ... accounting for approximately 93% of global production, followed by Canada with 5%''; World Mine Production table (2025e world total 112,000 t niobium content); Recycling; Substitutes'
  - subject: Tantalum (feedstock for Ta2O5)
    producers:
      - country: Congo (Kinshasa)
        share_percent: 52
        year: 2025
      - country: Rwanda
        share_percent: 16
        year: 2025
      - country: Nigeria
        share_percent: 15.6
        year: 2025
    critical_lists:
      - list: USGS 2025 List of Critical Minerals
        listed: true
      - list: EU critical raw materials list (Regulation (EU) 2024/1252, as shown on the European Commission page)
        listed: true
    recycling: 'USGS tantalum chapter: tantalum was recycled mostly from new scrap in capacitor manufacture; recycling may account for as much as 30 percent of consumption by domestic primary processors.'
    substitutes:
      - 'USGS tantalum chapter: aluminum, ceramics and niobium can substitute in electronic capacitors, with a performance loss or higher cost.'
    source: usgs-mcs2026-tantalum
    where: 'World Mine Production table (2025e: Congo (Kinshasa) 1,300 t, Rwanda 400 t, Nigeria 390 t, world total 2,500 t tantalum content); shares calculated by Space Mushroom against the 2,500 t total; Recycling; Substitutes'
documents:
  - title: 'PubChem: Niobium pentoxide (CID 9903420), experimental properties and GHS classification'
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/compound/9903420
    year: 2026
  - title: 'PubChem: Tantalum pentoxide (CID 62157), experimental properties and GHS classification'
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/compound/62157
    year: 2026
  - title: 'Lorad Chemical safety data sheet: Niobium Pentoxide (item NB-4490)'
    type: sds
    url: https://loradchemical.com/data/sds/SDS-Niobium-Pentoxide.pdf
    year: 2026
  - title: Triple Conductive Wiring by Electron Doping, Chelation Coating and Electrochemical Conversion in Fluffy Nb2O5 Anodes for Fast-Charging Li-Ion Batteries (Advanced Science 9, 2202201; PMC9443447)
    type: paper
    url: https://pmc.ncbi.nlm.nih.gov/articles/PMC9443447/
    year: 2022
  - title: Optical properties of Ta2O5 single layer and ultraviolet reflective film under ultraviolet irradiation (Optoelectronics Letters, vol. 17, 2021)
    type: paper
    url: https://www.researching.cn/ArticlePdf/m00050/2021/17/8/OEL-2021-08-0464.pdf
    year: 2021
  - title: NASA guidelines for screening, lot acceptance and derating of polymer tantalum capacitors (NASA TP, 2023; NTRS 20220019033)
    type: report
    url: https://ntrs.nasa.gov/api/citations/20220019033/downloads/20220019033-Teverovsky-2023-NASA-TP-Guidelines-Screening-PTC_v3.pdf
    year: 2023
  - title: 'USGS Mineral Commodity Summaries 2026: Niobium (Columbium)'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-niobium.pdf
    year: 2026
  - title: 'USGS Mineral Commodity Summaries 2026: Tantalum'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-tantalum.pdf
    year: 2026
  - title: NIST standard atomic weights table (Nb, Ta, O rows)
    type: database
    url: https://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl?ele=Nb&all=all&ascii=html
    year: 2026
gaps:
  - No refractive index for Nb2O5 was read in a fetched page. Search snippets give 2.0 to 2.3 at 550 nm for sputtered films, but none of those pages was opened, so no value is included.
  - No dielectric constant for Ta2O5 was read in a fetched page. Wikipedia's figure of about 25 is not used because Wikipedia is limited to composition and history for this brief, and the vendor page is not independent.
  - No Ta2O5 battery-anode value was read. The 2023 Nanoscale Advances paper on Ta2O5 with TaC (open access) was not readable through the fetch tool, so the anode data in this profile are for Nb2O5 only.
  - No Nb2O5 capacitor-dielectric source was read. The capacitor use in this profile is for Ta2O5, from the NASA guideline.
  - The Optica 2025 Ta2O5 optical-constants paper (DOI 10.1364/OME.550708) returned a bot-check page, so it was not used.
  - The extinction coefficients in the 2021 Ta2O5 paper are printed as powers of ten, so they are left out.
  - The 2021 Ta2O5 paper's sample is one 400 nm film made by electron-beam evaporation. The optical values describe that film, not bulk Ta2O5.
  - The T-Nb2O5 cycling values are for a modified material (polydopamine-etched, cobalt-doped, chelation-coated). Pristine Nb2O5 was not measured in the source used.
  - The reference electrode for the 1.0 to 3.0 V intercalation range is not stated in the paper.
  - No Nb2O5 or Ta2O5 thermal expansion, band gap, crustal abundance or recrystallisation data were read in a fetched source.
  - Hazard data for Ta2O5 rest on the PubChem summary only; no Ta2O5 supplier SDS was read.
  - The Nb2O5 acid attack (dissolution in hydrofluoric acid) is not included, because the source is Wikipedia and was not checked against a fetched supplier or database page.
  - The USGS 2025 critical list and the EU critical raw materials list were read through a summarising fetch rather than as raw page text. Both place niobium and tantalum on the list.
  - Custom benchmark names are used for intercalation_potential, reversible_capacity, rate_capacity, areal_capacity and interlayer_distance. They are not in spores/property-canon.yaml.
  - 'Atomic weights in the recipe are NIST standard values: Nb 92.90637, O 15.999 (NIST gives a range from 15.99903 to 15.99977). Ta 180.94788 is not used in a recipe part.'
sources:
  pubchem-nb2o5:
    title: PubChem compound record, Niobium pentoxide (CID 9903420; experimental properties and GHS classification)
    id: CID 9903420; CAS 1313-96-8; formula Nb2O5
    url: https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/9903420/JSON?heading=Experimental+Properties
    year: 2026
    kind: database
    license: public domain (NCBI)
  pubchem-ta2o5:
    title: PubChem compound record, Tantalum pentoxide (CID 62157; experimental properties and GHS classification)
    id: CID 62157; CAS 1314-61-0; formula O5Ta2
    url: https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/62157/JSON?heading=Experimental+Properties
    year: 2026
    kind: database
    license: public domain (NCBI)
  lorad-nb2o5-sds:
    title: Lorad Chemical safety data sheet, Niobium Pentoxide (item NB-4490)
    id: CAS 1313-96-8; Lorad Chemical
    url: https://loradchemical.com/data/sds/SDS-Niobium-Pentoxide.pdf
    year: 2026
    kind: datasheet
    license: supplier document, linked not reproduced
  pmc-tnb2o5-2022:
    title: Triple Conductive Wiring by Electron Doping, Chelation Coating and Electrochemical Conversion in Fluffy Nb2O5 Anodes for Fast-Charging Li-Ion Batteries (Advanced Science, 2022)
    id: doi:10.1002/advs.202202201; PMID 35798318; PMC9443447
    url: https://pmc.ncbi.nlm.nih.gov/articles/PMC9443447/
    year: 2022
    kind: paper
    license: CC BY 4.0
  ope-ta2o5-2021:
    title: Optical properties of Ta2O5 single layer and ultraviolet reflective film under ultraviolet irradiation (Optoelectronics Letters, vol. 17, no. 8, 2021; Xu Lingmao et al.)
    id: doi:10.1007/s11801-021-0157-8
    url: https://www.researching.cn/ArticlePdf/m00050/2021/17/8/OEL-2021-08-0464.pdf
    year: 2021
    kind: paper
    license: journal article, cited not reproduced
  nasa-ptc-2023:
    title: Guidelines for screening, lot acceptance and derating of polymer tantalum capacitors (A. Teverovsky, NASA Goddard technical publication, 2023)
    id: NTRS 20220019033
    url: https://ntrs.nasa.gov/api/citations/20220019033/downloads/20220019033-Teverovsky-2023-NASA-TP-Guidelines-Screening-PTC_v3.pdf
    year: 2023
    kind: report
    license: public domain (NASA)
  usgs-mcs2026-niobium:
    title: Mineral Commodity Summaries 2026, Niobium (Columbium)
    id: USGS MCS 2026, February 2026
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-niobium.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
  usgs-mcs2026-tantalum:
    title: Mineral Commodity Summaries 2026, Tantalum
    id: USGS MCS 2026, February 2026
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-tantalum.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
  nist-atomic-weights:
    title: NIST Atomic Weights and Isotopic Compositions for All Elements (standard atomic weights, Nb, Ta, O)
    id: NIST Physical Measurement Laboratory
    url: https://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl?ele=Nb&all=all&ascii=html
    year: 2026
    kind: database
    license: public domain (NIST)
  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)
  ec-crm:
    title: Critical raw materials (European Commission, list of critical raw materials)
    id: Regulation (EU) 2024/1252
    url: https://single-market-economy.ec.europa.eu/sectors/raw-materials/areas-specific-interest/critical-raw-materials_en
    year: 2024
    kind: web
    license: European Commission web page
license: CC-BY-4.0
updated: '2026-10-26'
review:
  status: draft
  method: assistant
  checked_values: 15
  unreachable: 2
  caveats: 4
  note: 'Read by an AI assistant on 2026-10-26 from pages and PDFs fetched in that run. PubChem values come from its JSON record, because the HTML page is scripted. The Optica 2025 optical-constants paper returned a bot-check page, and the RSC Ta2O5-TaC anode paper returned no article text, so neither was used. The USGS 2025 critical list and EU critical raw materials pages were read through a summarising fetch. Caveats: the anode values are for a modified T-Nb2O5, not pristine Nb2O5; the Ta2O5 optical values are for one 400 nm electron-beam film; the Nb2O5 melting point differs between PubChem (1500 °C) and the SDS (1521 °C).'
story:
  recipe:
    line: Nb2O5 combines two niobium atoms with five oxygen atoms, with niobium in the +5 state (4d0). In the orthorhombic T-phase, NbO6 and NbO7 units share corners through Nb-O-Nb bonds in a 'room and pillar' layered structure, with lithium entering between the layers. Ta2O5 has the same stoichiometry with tantalum in place of niobium. The Ta2O5 optical films in the 2021 study were made by electron-beam evaporation with an ion source.
    parts:
      - name: Niobium
        symbol: Nb
        atoms: 2
        atomic_weight: 92.90637
        role: The metal cation. Nb5+ (4d0) sits in NbO6 and NbO7 units that share corners to build the layers of the T-phase.
      - name: Oxygen
        symbol: O
        atoms: 5
        atomic_weight: 15.999
        role: The anion. Oxygen bridges neighbouring niobium atoms through Nb-O-Nb bonds, which hold the layers together.
  risk_groups:
    - title: For people
      level: 1
      verdict: Irritant powder; hazard classes differ by source
      lead: The supplier SDS classifies Nb2O5 powder as an irritant (H315, H319, H335). PubChem reports the same classes in about half of company reports and no classification in the rest.
      points:
        - label: The powder
          line: Warning. Skin, eye and breathing irritation, from the SDS and about half of PubChem reports.
        - label: Dust
          line: Avoid breathing dust. The SDS advises use outdoors or in a well-ventilated area.
        - label: Ta2O5
          line: Ta2O5 does not meet GHS hazard criteria in 97.5 percent of PubChem reports, but only 80 company reports were counted.
    - title: If a film or capacitor is heated or exposed
      lead: These results come from laboratory and screening tests, not from incidents in space.
      points:
        - label: Capacitor heating
          line: NASA's guideline says that slug temperatures of 100 to 150 °C during a power surge test can damage the Ta2O5 dielectric and cause a failure.
        - label: Vacuum ultraviolet
          line: A 400 nm Ta2O5 film kept its refractive index within 1 percent after 2000 ESH, and its transmittance from 300 to 500 nm fell from 81 to 79.4 percent.
    - title: Handling and storage
      points:
        - label: Storage
          line: Keep the container tightly closed in a dry, well-ventilated place, away from strong oxidizing agents.
        - label: Dust
          line: Avoid dust formation. In a fire, the SDS lists metal oxide fume as the decomposition product.
  why: Niobium pentoxide (Nb2O5) is a white, high-melting oxide that appears in three roles in this collection. Its orthorhombic T-phase has an open layered structure, through which lithium can move quickly, so a modified version works as a fast-charging anode. Tantalum pentoxide (Ta2O5), the same oxide type with tantalum, is a dielectric in tantalum capacitors and a stable optical film, and the 2021 study shows that its optical behaviour barely changes under vacuum ultraviolet. The anode results come from one research material that was modified on purpose, so they describe what the structure can do rather than a commercial cell.
  uses:
    - where: Fast-charging lithium-ion anodes
      line: A modified T-Nb2O5 anode, etched with polydopamine and doped with cobalt, kept 143 mAh/g at 1 A/g after 8500 cycles in a lithium cell and reached 144.1 mAh/g at 10.0 A/g.
    - where: Optical films for spacecraft
      line: A 2021 study tested 400 nm Ta2O5 films and UV-reflective multilayers under 2000 ESH of vacuum ultraviolet. The films kept their refractive index within 1 percent, and the reflective multilayer kept most of its reflectance.
    - where: Tantalum capacitors
      line: Ta2O5 is the dielectric in tantalum capacitors. NASA's screening guideline for polymer tantalum capacitors describes the Ta2O5 dielectric and the power surge test that can damage it.
  can_do:
    - label: Fast charging
      value: 144.1 mAh/g at 10.0 A/g
      line: A modified T-Nb2O5 anode gave 144.1 mAh/g at 10.0 A/g in a lithium cell. The paper says pristine T-Nb2O5 was limited by low electronic conductivity.
    - label: Cycle life
      value: 143 mAh/g after 8500 cycles
      line: The same modified anode kept 143 mAh/g at 1 A/g after 8500 cycles. That is a laboratory cell result, not a field life.
    - label: Optical stability
      value: Index change below 1 percent
      line: A 400 nm Ta2O5 film changed its refractive index at 500 nm from 2.0914 to 2.1116 after 2000 ESH of vacuum ultraviolet.
    - label: Heat tolerance
      value: Melts at 1500 to 1872 °C
      line: Nb2O5 melts at 1500 °C (PubChem) or 1521 °C (SDS). Ta2O5 melts at 1872 °C (PubChem).
  compare: Nb2O5 and Ta2O5 share a formula type but differ in mass and melting point. Ta2O5 is denser, at 8.2 g/cm3 against 4.6 g/cm3 for Nb2O5, and melts at 1872 °C in PubChem against 1500 to 1521 °C for Nb2O5. The table compares melting point, density and refractive index, where the refractive index is available only for Ta2O5.
  compare_rows:
    - label: Melting point
      benchmark: melting_point
    - label: Density
      benchmark: density
    - label: Refractive index
      benchmark: refractive_index
  handling:
    - Keep the container tightly closed in a dry, well-ventilated place, away from strong oxidizing agents.
    - Avoid dust formation, and use exhaust ventilation or outdoor use where dust can form.
    - Wear gloves and eye protection. The SDS classes the powder as an irritant.
  good_for:
    - Fast-charging anodes. A modified T-Nb2O5 anode reached 144.1 mAh/g at 10.0 A/g in a lithium cell.
    - Vacuum-ultraviolet-stable oxide optical films. A Ta2O5 film kept its refractive index within 1 percent after 2000 ESH.
    - Dielectric layers in tantalum capacitors, where Ta2O5 is the standard dielectric.
  watch_out:
    - Pristine T-Nb2O5 has low electronic conductivity. The anode paper needed doping, etching and coating to reach its high-rate results.
    - Capacitor heating. NASA's guideline says a surge test that heats the slug to 100 to 150 °C can damage the Ta2O5 dielectric.
    - The melting point of Nb2O5 differs by about 20 °C between PubChem and the SDS. Check the grade you buy.
  verdict: Nb2O5 is a useful high-rate anode oxide, but the best data come from a modified research material, not a commercial powder. Ta2O5 is the stronger case for space, through its capacitor and optical-film record, and its optical behaviour held up well under vacuum ultraviolet.