spore: profile
id: nickel-oxide
spore_version: 0.2
family: oxide-ceramics
name: Nickel oxide
abbreviation: NiO
role: p-type oxide for transparent layers, solid oxide fuel cell anodes and oxide scales on nickel; carcinogen
category: ceramics
type: oxides
summary: |
  Nickel(II) oxide (NiO) is a green-to-black oxide with a face-centred cubic rock-salt structure. Its lattice constant is 4.169 Å at 298 K, its density is 6.67 g/cm3, and one supplier safety data sheet gives a melting point of 1984 °C. It is practically insoluble in water (0.00003 g/l at 20 °C). Sputtered NiO films are p-type conductors: a 110 nm film on glass reached 7.2 S/cm with 40 percent average transmittance, and a 100 nm RF-sputtered film reached 9.09 S/cm with 69 percent. Porous Ni/YSZ and NiO/YSZ composites have been studied for solid oxide fuel cell anodes. Nickel heated in oxygen forms a NiO scale that grows outward and carries a compressive grain-boundary stress of about 10 MN/m2 at 1000 °C. NiO is a carcinogen hazard: the Sigma-Aldrich safety data sheet gives H350, and IARC places nickel compounds in Group 1.
best_for: p-type transparent conducting films and nickel-based solid oxide fuel cell anode work, under strict dust and inhalation controls
weakest_at: Low conductivity in sputtered films (7.2 to 9.09 S/cm) and a carcinogen hazard (H350, with IARC Group 1 for nickel compounds)
identity:
  formula: NiO
  cas: 1313-99-1
  crystal_system: cubic
  space_group: Fm3m
  source: vidal-2005-nio
  where: Experimental Procedures, paragraph beginning 'No antiferromagnetic distortion' (face-centred cubic, Fm3m, lattice constant 4.169(2) Å at 298 K); CAS number in Section 3 of sigma-sds-nio
tags:
  environments: []
  stresses:
    - extreme-heat
  applications:
    - electronics-and-chips
    - batteries
    - propulsion-and-tanks
properties:
  - benchmark: density
    label: Relative density, nickel(II) oxide (Sigma-Aldrich SDS)
    value: 6.67
    unit: g/cm3
    scope: material
    conditions:
      temperature: 25 °C (77 °F)
      grade: powder, Sigma-Aldrich product 637130
    method: Value printed in a supplier safety data sheet as relative density
    status: ground
    source: sigma-sds-nio
    where: Section 9 (Physical and Chemical Properties), item m) Relative density
  - benchmark: density
    label: Density, nickel oxide (Angstrom Sciences SDS)
    value: 6.67
    unit: g/cm3
    scope: material
    conditions:
      grade: powder, sputtering target and custom parts, as listed in the SDS
    method: Value printed in a supplier safety data sheet
    status: ground
    source: angstrom-sds-nio
    where: Section 9 (Physical and Chemical Properties), Density row (printed as 6.67 g/cc)
  - benchmark: melting_point
    label: Melting point, nickel oxide (Angstrom Sciences SDS)
    value: 1984
    unit: °C
    scope: material
    conditions:
      grade: powder, as listed in the SDS
    method: Value printed in a supplier safety data sheet
    status: ground
    note: The Sigma-Aldrich SDS for the same compound gives melting point as No data available, so this value rests on one reseller sheet.
    source: angstrom-sds-nio
    where: Section 9 (Physical and Chemical Properties), Melting Point row
  - benchmark: molar_mass
    label: Molecular weight, nickel oxide (computed)
    value: 74.693
    unit: g/mol
    scope: material
    conditions:
      basis: computed property in the database record
    method: Computed molecular weight printed in the PubChem record
    status: calculated
    source: pubchem-nio
    where: Chemical and Physical Properties, Computed Properties, Molecular Weight
  - benchmark: water_solubility
    label: Water solubility, nickel oxide at 20 °C
    value: 0.00003
    unit: g/l
    scope: material
    conditions:
      temperature: 20 °C (68 °F)
    method: OECD Test Guideline 105, as printed in the supplier safety data sheet
    status: ground
    note: The SDS describes the product as practically insoluble.
    source: sigma-sds-nio
    where: Section 9, item n) Water solubility
  - benchmark: band_gap
    label: Optical band gap, single-crystal NiO (range)
    value: 3.6
    value_high: 4
    bound: range
    unit: eV
    scope: material
    conditions:
      crystal: single crystal
      temperature: not stated in the review
    method: Range stated in a 2024 review of p-type transparent conducting oxides
    status: ground
    source: arxiv-ptco-2024
    where: Section on NiO, sentence beginning 'However, the optical band energy of single-crystal NiO', citing reference [5] of the review
  - benchmark: band_gap
    label: Optical band gap, 110 nm sputtered NiO film on glass
    value: 3.8
    unit: eV
    scope: material
    conditions:
      film_thickness: 110 nm
      substrate: glass
      deposition: magnetron sputtering
    method: Value tabulated in a 2024 review (Table 4) from the study it cites as reference [5]
    status: ground
    source: arxiv-ptco-2024
    where: Table 4 (Binary oxide materials as p-type TCO), NiO row, magnetron sputtering
  - benchmark: electrical_conductivity
    label: Electrical conductivity, 110 nm sputtered NiO film
    value: 7.2
    unit: S/cm
    scope: material
    conditions:
      film_thickness: 110 nm
      substrate: glass
      deposition: magnetron sputtering
    method: Value tabulated in a 2024 review (Table 4)
    status: ground
    source: arxiv-ptco-2024
    where: Table 4, NiO row, electrical conductivity column (S/cm)
  - benchmark: optical_transmittance
    label: Average transmittance, 110 nm sputtered NiO film
    value: 40
    unit: '%'
    scope: material
    conditions:
      film_thickness: 110 nm
      substrate: glass
      deposition: magnetron sputtering
    method: Value tabulated in a 2024 review (Table 4)
    status: ground
    source: arxiv-ptco-2024
    where: Table 4, NiO row, average transmittance column
  - benchmark: electrical_conductivity
    label: Electrical conductivity, 100 nm RF-sputtered NiO film
    value: 9.09
    unit: S/cm
    scope: material
    conditions:
      film_thickness: 100 nm
      substrate: glass
      deposition: RF magnetron sputtering
    method: Value tabulated in a 2024 review (Table 4)
    status: ground
    source: arxiv-ptco-2024
    where: Table 4, NiO RFMS row (reference [96]), electrical conductivity column
  - benchmark: optical_transmittance
    label: Average transmittance, 100 nm RF-sputtered NiO film
    value: 69
    unit: '%'
    scope: material
    conditions:
      film_thickness: 100 nm
      substrate: glass
      deposition: RF magnetron sputtering
    method: Value tabulated in a 2024 review (Table 4)
    status: ground
    source: arxiv-ptco-2024
    where: Table 4, NiO RFMS row (reference [96]), average transmittance column
  - benchmark: hall_mobility
    label: Hall mobility, 100 nm RF-sputtered NiO film
    value: 6.12
    unit: cm2/V-s
    scope: material
    conditions:
      film_thickness: 100 nm
      substrate: glass
      deposition: RF magnetron sputtering
    method: Value tabulated in a 2024 review (Table 4)
    status: ground
    source: arxiv-ptco-2024
    where: Table 4, NiO RFMS row (reference [96]), Hall mobility column
  - benchmark: lattice_constant_a
    label: Lattice constant a, NiO single crystal at 298 K
    value: 4.169
    unit: Å
    scope: material
    conditions:
      crystal: single crystal, face-centred cubic (Fm3m)
      temperature: 298 K
    method: Least-squares refinement of X-ray diffraction data, printed as 4.169(2) Å
    status: ground
    note: The paper prints the uncertainty as (2) in the last digit.
    source: vidal-2005-nio
    where: Experimental Procedures, paragraph after the structure factor table, sentence beginning 'Least-squares refinement'
corrosion:
  - environment: Nickel heated in dry oxygen at 1000 °C (NiO scale on nickel)
    headline: The NiO scale grows outward and pushes sideways with a stress of about 10 MN/m2, so it is not a passive layer.
    effect: The NASA report says nickel oxide growing on nickel in oxygen at 1000 °C has a mean grain-boundary pressure of approximately 10 MN/m2, and that the scale is not passive because it generates a lateral compressive stress during oxidation. The scale thickens almost exclusively by outward diffusion of metal ions through the oxide.
    rating: moderate
    conditions:
      temperature: 1000 °C
      atmosphere: oxygen
      substrate: nickel (Nickel-201 and Nickel-270 in the report)
    source: nasa-tn-d5266
    where: 'Section ''Case 2: The active surface layer'' (page 8), and the introduction, point (3)'
  - environment: Ni/NiO-YSZ composites in a solid oxide fuel cell anode, through burnout and redox cycling
    headline: Nickel expands when it oxidises, so the anode composition has to stay within a window that also avoids thermal mismatch with the electrolyte.
    effect: The Waterloo thesis abstract says the composites made from nickel metal expand due to nickel oxidation during burnout, while the composites that started from NiO change little in volume on reduction when YSZ is present. It limits nickel loading to a window with a minimum for electrical conductivity and a maximum to avoid thermal mismatch with YSZ.
    rating: moderate
    conditions:
      nickel_loading: 4 to 77 vol% of total solids (range studied)
      process: burnout and reduction of porous composites
    source: clemmer-2006-nio-ysz
    where: Abstract
  - environment: Water (practically insoluble)
    headline: The supplier SDS shows negligible dissolution in water, but gives no corrosion rate.
    effect: The Sigma-Aldrich SDS gives a water solubility of 0.00003 g/l at 20 °C and describes the product as practically insoluble. The SDS gives no corrosion rate, so the rating is unknown.
    rating: unknown
    conditions:
      temperature: 20 °C
    source: sigma-sds-nio
    where: Section 9, item n) Water solubility
risks:
  hazards:
    - text: The Sigma-Aldrich SDS classes nickel(II) oxide as Danger with H317 (allergic skin reaction), H350 (may cause cancer), H372 (organ damage through prolonged or repeated exposure) and H413 (long-lasting harm to aquatic life).
      ghs:
        - H317
        - H350
        - H372
        - H413
      source: sigma-sds-nio
      where: Section 2 (Hazards identification), GHS classification
    - text: PubChem's summary of ECHA notifications gives the same four codes, with H317 in 100 percent of classifying notifications and H350 in 98.9 percent. The record title reads Nickel trioxide, but the formula NiO and CAS 1313-99-1 match nickel(II) oxide.
      ghs:
        - H317
        - H350
        - H372
        - H413
      source: pubchem-nio
      where: Safety and Hazards, GHS Classification, ECHA C&L Notifications Summary
    - text: A Solaronix SDS for a nickel oxide paste (Ni-Nanoxide N/SP, nickel monoxide 10 to 25 percent) classes it as Danger with H315, H317, H350i (cancer by inhalation), H372 and H413. It is a paste, so this is a product classification and not a pure NiO classification.
      ghs:
        - H315
        - H317
        - H350i
        - H372
        - H413
      source: solaronix-sds-nio
      where: Sections 2 and 3 (dangerous components)
    - text: IARC classifies nickel compounds in Group 1, carcinogenic to humans, with a definite link to lung, nasal and paranasal cancer. The CAREX Canada profile says the evaluation was mainly for nickel compounds containing oxygen and sulphur. The page does not name nickel oxide directly.
      ghs: []
      source: carex-nickel
      where: Nickel Profile, paragraph on IARC Monograph Vol. 100C (2012)
  failure_risks:
    - mode: Growth stress in a NiO scale on nickel at high temperature
      trigger: Heating nickel in oxygen at about 1000 °C for long periods
      consequence: The scale carries a compressive grain-boundary stress of about 10 MN/m2, which the NASA report models as a change to the high-temperature creep behaviour of the nickel beneath it.
      severity: moderate
      source: nasa-tn-d5266
      where: 'Section ''Case 2: The active surface layer'' (page 8)'
    - mode: Volume change of nickel in a fuel cell anode on redox cycling
      trigger: Oxidation of the nickel phase during burnout or a loss of reducing gas in service
      consequence: Expansion of the nickel phase can break the match with the YSZ electrolyte, so the nickel loading has to stay inside a narrow window.
      severity: moderate
      source: clemmer-2006-nio-ysz
      where: Abstract
  side_effects: []
  handling:
    - text: Avoid contact with skin and eyes and avoid forming dust. Provide exhaust ventilation where dust is formed. Combustible dust can form in further processing.
      source: sigma-sds-nio
      where: Section 7.1 (Precautions for safe handling)
    - text: Handle and store under inert gas, in a dry place.
      source: sigma-sds-nio
      where: Section 7.2 (Conditions for safe storage)
    - text: Pick up spills without creating dust, sweep up or shovel, and keep the waste in closed containers.
      source: sigma-sds-nio
      where: Section 6 (Accidental release measures)
  mitigations:
    - text: 'Workplace limits in the SDS: OSHA PEL 1 mg/m3 TWA, NIOSH REL 0.015 mg/m3 TWA (potential occupational carcinogen), ACGIH TLV 0.2 mg/m3 TWA (confirmed human carcinogen, lung cancer).'
      source: sigma-sds-nio
      where: Section 8.1 (Control parameters)
    - text: NIOSH lists the IDLH for nickel metal and other compounds as 10 mg/m3 as Ni. The NIOSH entry does not state the basis for this value on the page read.
      source: niosh-npg-nickel
      where: IDLH heading of the NIOSH Pocket Guide entry
    - text: Where a risk assessment shows that respirators are needed, the SDS recommends a full-face particle respirator (N100 or P3 cartridges) as a backup to engineering controls.
      source: sigma-sds-nio
      where: Section 8.2 (Exposure controls), respiratory protection
uses:
  - application: electronics-and-chips
    device: p-type transparent conducting layer in transparent p-n junctions and thin-film transistors
    example: The 2024 review calls NiO the first p-type transparent conducting oxide. Sputtered NiO films in its Table 4 reach 7.2 S/cm with 40 percent transmittance (110 nm) and 9.09 S/cm with 69 percent transmittance (100 nm, RF sputtering).
    source: arxiv-ptco-2024
    where: Introduction and NiO discussion; Table 4, NiO rows
  - application: batteries
    device: Solid oxide fuel cell anode made from porous Ni/YSZ or NiO/YSZ composites
    example: A 2006 Waterloo thesis studied porous Ni/YSZ and NiO/YSZ composites for solid oxide fuel cells, with nickel loadings from 4 to 77 vol%. The abstract reports that nickel-metal composites expand on oxidation during burnout.
    source: clemmer-2006-nio-ysz
    where: Abstract
  - application: propulsion-and-tanks
    device: Oxide scale on nickel and nickel-base alloys in hot oxidising gas
    example: A NASA report on oxidation of nickel at 1000 °C models the growing NiO scale and says the results should carry over to complex nickel-base alloy systems. This is a stated expectation, not a measured alloy result.
    source: nasa-tn-d5266
    where: Introduction, point (4)
supply:
  - subject: Nickel (feedstock for NiO)
    producers:
      - country: Indonesia
        share_percent: 66.7
        year: 2025
      - country: Philippines
        share_percent: 6.9
        year: 2025
      - country: Russia
        share_percent: 5.1
        year: 2025
      - country: New Caledonia
        share_percent: 3.6
        year: 2025
      - country: Canada
        share_percent: 3.6
        year: 2025
      - country: China
        share_percent: 3.1
        year: 2025
      - country: Brazil
        share_percent: 1.8
        year: 2025
      - country: Australia
        share_percent: 1.2
        year: 2025
      - country: United States
        share_percent: 0.3
        year: 2025
    critical_lists:
      - list: USGS 2025 List of Critical Minerals (nickel is on the final list, used to make high-strength steel and rechargeable batteries)
        listed: true
    recycling: 'USGS: nickel recovered from scrap was about 60 percent of US apparent consumption in 2025, mostly from stainless-steel scrap.'
    substitutes:
      - 'USGS nickel chapter: low-nickel, duplex or ultrahigh-chromium stainless steels can replace austenitic grades, and titanium alloys can replace nickel-base alloys in corrosive environments.'
    source: usgs-mcs2026-nickel
    where: World Mine Production and Reserves table, 2025e column (world total 3,900,000 t, rounded); Recycling; Substitutes. The producer shares are calculated by Space Mushroom from each tonnage divided by the 3,900,000 t world total, not printed by USGS. USGS gives no NiO production table.
documents:
  - title: Sigma-Aldrich safety data sheet, nickel(II) oxide, product 637130 (Version 4.10, revision 28 February 2015; copy hosted by Utah NanoFab)
    type: sds
    url: https://www.nanofab.utah.edu/wp-content/uploads/2018/08/NickelII-oxide-Sigma-Aldrich-28Feb15_v4.1.pdf
    year: 2015
  - title: Angstrom Sciences safety data sheet, Nickel Oxide (CAS 1313-99-1; last revision 07/02/15)
    type: sds
    url: https://angstromsciences.com/wp-content/uploads/files/SDS/Nickel%20Oxide.pdf
    year: 2015
  - title: Solaronix safety data sheet, Ni-Nanoxide N/SP (nickel oxide paste, EU CLP format; printed 25.06.2013)
    type: sds
    url: https://www.solaronix.com/msds/MSDS_Ni-Nanoxide_N__SP.pdf
    year: 2013
  - title: PubChem compound record, CID 14805 (formula NiO, CAS 1313-99-1)
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/compound/14805
    year: 2026
  - title: 'Progress in Developing Highly Efficient p-Type TCOs for Transparent Electronics: A Comprehensive Review (arXiv 2405.14354)'
    type: paper
    url: https://arxiv.org/pdf/2405.14354
    year: 2024
  - title: 'Indications of the Magnetic State in the Charge Distributions of MnO, CoO, and NiO. III: Antiferromagnetism of NiO (Crystallography Reports, 2005)'
    type: paper
    url: https://www.mv.helsinki.fi/home/kurkisuo/6.1.A/05-NiO.pdf
    year: 2005
  - title: A Proposed Model for the Effect of Oxidation on the High-Temperature Deformation of Nickel (NASA TN D-5266)
    type: report
    url: https://ntrs.nasa.gov/api/citations/19690017683/downloads/19690017683.pdf
    year: 1969
  - title: The Processing and Characterization of Porous Ni/YSZ and NiO/YSZ Composites used in Solid Oxide Fuel Cell Applications (University of Waterloo, 2006)
    type: paper
    url: https://uwspace.uwaterloo.ca/handle/10012/2883
    year: 2006
  - title: CAREX Canada, Nickel profile (IARC Monograph Vol. 100C classification)
    type: report
    url: https://www.carexcanada.ca/?p=9614
    year: 2026
  - title: 'USGS Mineral Commodity Summaries 2026: Nickel'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-nickel.pdf
    year: 2026
  - title: NIOSH Pocket Guide, Nickel metal and other compounds (as Ni)
    type: report
    url: https://www.cdc.gov/niosh/npg/npgd0445.html
    year: 2026
gaps:
  - No battery-precursor source for NiO was read. The open-access 2022 review (Entwistle et al., Energy Reports) and the 2025 review describe hydroxide precursors milled with a lithium salt. A patent snippet says NiO forms as an intermediate when Ni(OH)2 is heated at 500 °C, but the patent was not fetched, so the battery-precursor use is not stated as a source-backed use.
  - The protective Cr2O3 scale and the spallation behaviour of NiO on Ni-Cr and Ni-Mo-Cr alloys were seen only in search snippets. No open alloy-oxidation source was opened, so the alloy claim is limited to the NASA statement that its results should apply to nickel-base alloys.
  - Bulk thermal expansion coefficient, thermal conductivity and the Néel temperature were not read in a fetched source in this run. The Néel temperature of 523 K appeared only in a search snippet.
  - Molar volume and the NiO/Ni volume change on reduction were in a 2011 MDPI review that returned HTTP 403, so they are not used.
  - The IARC Volume 100C monograph was not opened. The Group 1 statement rests on the CAREX Canada profile. The CAREX page does not name nickel oxide directly.
  - Atomic weights for nickel and oxygen were not read in a source opened for this profile, so the recipe parts carry no atomic_weight.
  - Acid and base attack rates were not found in a source read in this run.
  - The PubChem record CID 14805 has the title Nickel trioxide while the formula and CAS number match nickel(II) oxide; PubChem's own melting point and density were not used because the experimental-properties page returned a verification screen.
  - Electrical conductivity, band gap, water solubility, molar mass, Hall mobility and lattice constant are not in property-canon.yaml; snake_case names were used, as in zinc-oxide.yaml.
  - The H350 (Sigma-Aldrich, PubChem) and H350i (Solaronix paste) classifications differ; both are kept with their source.
  - The melting point of 1984 °C comes from one reseller SDS; the Sigma-Aldrich SDS gives no melting point.
  - The NASA Tech Brief on black nickel plating (1974) describes a nickel plating process, not NiO, and was not used.
  - No flight, vacuum or space-exposure result for NiO was found in the sources read.
  - The EU critical raw materials list was not checked for nickel. Crustal abundance of nickel was not read.
sources:
  pubchem-nio:
    title: PubChem compound record, CID 14805 (formula NiO, CAS 1313-99-1; record title reads Nickel trioxide)
    id: CID 14805
    url: https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/14805/JSON
    year: 2026
    kind: database
    license: public domain (NCBI)
  sigma-sds-nio:
    title: Sigma-Aldrich safety data sheet, nickel(II) oxide, product 637130 (Version 4.10, revision 28 February 2015)
    id: CAS 1313-99-1, product 637130
    url: https://www.nanofab.utah.edu/wp-content/uploads/2018/08/NickelII-oxide-Sigma-Aldrich-28Feb15_v4.1.pdf
    year: 2015
    kind: datasheet
    license: supplier document, linked not reproduced
  angstrom-sds-nio:
    title: Angstrom Sciences safety data sheet, Nickel Oxide (last revision 07/02/15)
    id: CAS 1313-99-1, EC 215-215-7
    url: https://angstromsciences.com/wp-content/uploads/files/SDS/Nickel%20Oxide.pdf
    year: 2015
    kind: datasheet
    license: supplier document, linked not reproduced
  solaronix-sds-nio:
    title: Solaronix safety data sheet, Ni-Nanoxide N/SP (nickel oxide paste)
    id: printed 25.06.2013, version 1
    url: https://www.solaronix.com/msds/MSDS_Ni-Nanoxide_N__SP.pdf
    year: 2013
    kind: datasheet
    license: supplier document, linked not reproduced
  arxiv-ptco-2024:
    title: 'Progress in Developing Highly Efficient p-Type TCOs for Transparent Electronics: A Comprehensive Review (Singh and Bhardwaj)'
    id: arXiv 2405.14354
    url: https://arxiv.org/pdf/2405.14354
    year: 2024
    kind: paper
    license: arXiv preprint (cited, not reproduced)
  vidal-2005-nio:
    title: 'Indications of the Magnetic State in the Charge Distributions of MnO, CoO, and NiO. III: Antiferromagnetism of NiO (Vidal, Vidal-Valat and Kurki-Suonio; Crystallography Reports, vol. 50, no. 1, 2005)'
    id: Crystallography Reports 50(1), pp. 20 to 26
    url: https://www.mv.helsinki.fi/home/kurkisuo/6.1.A/05-NiO.pdf
    year: 2005
    kind: paper
    license: not stated on the copy read
  nasa-tn-d5266:
    title: A Proposed Model for the Effect of Oxidation on the High-Temperature Deformation of Nickel (James S. Wolf, NASA TN D-5266, Lewis Research Center)
    id: NTRS 19690017683
    url: https://ntrs.nasa.gov/api/citations/19690017683/downloads/19690017683.pdf
    year: 1969
    kind: report
    license: public domain (NASA)
  clemmer-2006-nio-ysz:
    title: The Processing and Characterization of Porous Ni/YSZ and NiO/YSZ Composites used in Solid Oxide Fuel Cell Applications (Ryan Clemmer, University of Waterloo)
    id: UWSpace handle 10012/2883
    url: https://uwspace.uwaterloo.ca/handle/10012/2883
    year: 2006
    kind: paper
    license: not stated on the repository page
  carex-nickel:
    title: CAREX Canada, Nickel profile
    id: CAREX Canada nickel profile
    url: https://www.carexcanada.ca/?p=9614
    year: 2026
    kind: web
    license: not stated
  usgs-mcs2026-nickel:
    title: Mineral Commodity Summaries 2026, Nickel
    id: USGS MCS 2026
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-nickel.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
    url: https://www.usgs.gov/programs/mineral-resources-program/science/about-2025-list-critical-minerals
    year: 2025
    kind: web
    license: public domain (USGS)
  niosh-npg-nickel:
    title: NIOSH Pocket Guide to Chemical Hazards, Nickel metal and other compounds (as Ni)
    id: NIOSH NPG entry npgd0445; CAS 7440-02-0 (metal)
    url: https://www.cdc.gov/niosh/npg/npgd0445.html
    year: 2026
    kind: handbook
    license: public domain (CDC)
license: CC-BY-4.0
updated: '2026-10-26'
review:
  status: draft
  method: assistant
  checked_values: 13
  unreachable: 4
  caveats: 6
  note: 'Read by an AI assistant on 2026-10-26 from the pages and PDFs fetched in that run. Two MDPI papers (the SOFC redox review and the p-type Ni1-xO film paper) returned HTTP 403, and the IARC Volume 100C PDF did not download. The PubChem experimental-properties page returned a verification screen. The Solaronix SDS is for a paste, not pure NiO. The melting point comes from one reseller SDS. Caveats: the Membranes review and the Coatings paper are not used; the battery-precursor use is not sourced; the alloy-scale statements rest on the NASA report and a search snippet only.'
story:
  recipe:
    line: NiO is a 1:1 compound of nickel and oxygen. It crystallises in the face-centred cubic rock-salt structure (space group Fm3m), with a lattice constant of 4.169 Å at 298 K. Simple rock-salt structure is one reason the 2024 review gives for its use as a p-type transparent conductor.
    parts:
      - name: Nickel
        symbol: Ni
        role: The metal cation. Ni(II) ions sit in the rock-salt lattice with oxygen as the counter-ion.
      - name: Oxygen
        symbol: O
        role: The anion. Oxygen forms the other half of the rock-salt lattice with nickel.
  risk_groups:
    - title: For people
      level: 1
      verdict: Cancer risk by inhalation; skin sensitiser
      lead: The supplier safety data sheets classify nickel oxide as a Danger-level carcinogen and skin sensitiser. IARC places nickel compounds in Group 1.
      points:
        - label: Inhalation
          line: The Sigma-Aldrich SDS gives H350 (may cause cancer) and H372 (organ damage from repeated exposure). The paste SDS gives H350i (cancer by inhalation).
        - label: Dust limits
          line: OSHA PEL 1 mg/m3, NIOSH REL 0.015 mg/m3 (potential carcinogen), and ACGIH TLV 0.2 mg/m3 are the workplace limits printed in the SDS.
        - label: Skin
          line: H317 means it can cause an allergic skin reaction.
    - title: If the oxide is heated or cycled
      lead: High-temperature oxidation and redox cycling change the stress and the volume of nickel-based parts.
      points:
        - label: Scale stress
          line: On nickel at 1000 °C in oxygen, the NiO scale carries a compressive stress of about 10 MN/m2.
        - label: Anode cycling
          line: In Ni/YSZ composites, nickel expands when it oxidises, so the nickel loading has to stay in a window.
    - title: Handling and storage
      points:
        - label: Dust
          line: Avoid dust formation and provide exhaust ventilation. Clean up spills without creating dust.
        - label: Storage
          line: Handle and store under inert gas, in a dry place, as the Sigma-Aldrich SDS says.
  why: 'Nickel oxide is a simple rock-salt oxide and the p-type counterpart to n-type transparent oxides such as zinc oxide. Its record in the sources read is in three places: sputtered films that conduct as p-type layers (7.2 and 9.09 S/cm, with 40 to 69 percent transmittance), porous Ni/YSZ and NiO/YSZ composites studied as solid oxide fuel cell anodes, and a NiO scale on nickel that builds a compressive stress of about 10 MN/m2 at 1000 °C. Its weak point is the hazard: the SDS classes it as a carcinogen and IARC places nickel compounds in Group 1. No flight or space-exposure data for NiO was found.'
  uses:
    - where: Transparent p-type layers
      line: The 2024 review calls NiO the first p-type transparent conducting oxide. It is mostly used in transparent p-n junctions and thin-film transistors.
    - where: Solid oxide fuel cell anodes
      line: A 2006 Waterloo thesis studied porous Ni/YSZ and NiO/YSZ composites with nickel loadings from 4 to 77 vol%, and found the nickel loading must stay in a window to keep conductivity and avoid thermal mismatch with the electrolyte.
    - where: Oxide scale on nickel and nickel alloys
      line: A NiO scale on nickel at 1000 °C in oxygen carries a compressive stress of about 10 MN/m2. The NASA report expects its results to apply to nickel-base alloys.
  can_do:
    - label: p-type conduction
      value: 7.2 S/cm at 110 nm
      line: A 110 nm sputtered NiO film on glass conducts at 7.2 S/cm with 40 percent average transmittance.
    - label: Higher conductivity film
      value: 9.09 S/cm at 100 nm
      line: An RF-sputtered 100 nm NiO film reached 9.09 S/cm, 69 percent transmittance and 6.12 cm2/V-s Hall mobility.
    - label: Crystal cell
      value: 4.169 Å cubic lattice
      line: The rock-salt cell has a lattice constant of 4.169 Å at 298 K from X-ray refinement.
    - label: Scale stress
      value: about 10 MN/m2 at 1000 °C
      line: Nickel oxide grown on nickel in oxygen at 1000 °C carries a grain-boundary pressure of about 10 MN/m2.
  compare: 'Compared with zinc oxide, nickel oxide melts at a higher temperature and is denser, as the compare rows show. Its sputtered-film conductivity (7.2 to 9.09 S/cm) is for an undoped p-type film, so it is not directly comparable with the doped n-type zinc oxide films. The main difference is the hazard: zinc oxide is classed only as an aquatic hazard in its SDS, while nickel oxide carries a carcinogen classification.'
  compare_rows:
    - label: Melting point
      benchmark: melting_point
    - label: Density
      benchmark: density
    - label: Band gap
      benchmark: band_gap
  handling:
    - Avoid dust and use exhaust ventilation.
    - Handle and store under inert gas in a dry place.
    - Treat it as a carcinogen and keep exposure within the OSHA, NIOSH and ACGIH limits printed in the SDS.
  good_for:
    - Undoped p-type transparent layers in research devices, at 7.2 to 9.09 S/cm in sputtered films.
    - Nickel-based solid oxide fuel cell anode work, where the NiO/YSZ composite is the starting material.
    - Studying oxide scale growth on nickel at high temperature, where the scale stress is about 10 MN/m2 at 1000 °C.
  watch_out:
    - 'The carcinogen classification: H350 in the Sigma-Aldrich SDS, H350i in the paste SDS, and IARC Group 1 for nickel compounds.'
    - Volume change of nickel on oxidation in anodes, and the scale growth stress on nickel.
    - Hazard classes differ between the SDS sheets read, and the PubChem summary is mixed.
  verdict: Nickel oxide is a simple, well-characterised p-type oxide, with film conductivity of about 7 to 9 S/cm in the sources read. Its carcinogen classification and dust hazard make it a controlled material. It has no flight record, and the battery-precursor use is not backed by a source read in this run, so it is listed as a gap.