{
  "spore": "profile",
  "id": "nb3sn",
  "spore_version": "0.2",
  "family": "magnet-and-superconducting-alloys",
  "name": "Niobium-tin (Nb3Sn)",
  "abbreviation": "Nb3Sn",
  "role": "A15 superconductor wire for high-field magnets",
  "category": "metals",
  "type": "refractory-metals",
  "summary": "Niobium-tin (Nb3Sn) is an intermetallic superconductor with the A15 crystal structure. The highest critical temperature reported for it is 18.3 K (Hanak et al., 1964, quoted in a 2006 review). Its upper critical field, extrapolated to 0 K, is about 29 T for the highest-tin ternary wires in the review. State-of-the-art Ta- and Ti-doped strands reach about 24 to 26.5 T at 4.2 K (Physical Review Materials, 2024). ITER's toroidal-field and central-solenoid magnets use Nb3Sn cable, and CERN reports that Nb3Sn will allow the HL-LHC quadrupoles to reach fields as high as 11.5 T.\n",
  "best_for": "Superconducting magnets at about 11 to 13 T and 4 K, where NbTi cannot carry the needed current density (ITER central solenoid designed for 13 T)",
  "weakest_at": "Brittleness and strain: large strain causes irreversible cracking of the A15 layer, and the critical current of present conductors falls off swiftly above 12 to 15 T (PRM 2024). The fine powder is also a flammable solid (supplier SDS).",
  "identity": {
    "formula": "Nb3Sn",
    "cas": "12035-04-0",
    "crystal_system": "cubic A15 (A3B type, Sn atoms on a bcc sublattice)",
    "designations": [],
    "source": "ae-nb3sn",
    "where": "Section 3.1 (CAS 12035-04-0, Niobium tin powder) and Chemical Identifiers (linear formula Nb3Sn, PubChem CID 15251588); crystal structure from godeke2006, text on the A15 lattice and the cubic and tetragonal phases"
  },
  "tags": {
    "environments": [],
    "stresses": [
      "extreme-cold"
    ],
    "applications": [
      "electronics-and-chips"
    ]
  },
  "properties": [
    {
      "benchmark": "critical_temperature",
      "label": "Critical temperature, highest value reported for Nb3Sn",
      "value": 18.3,
      "bound": "exact",
      "unit": "K",
      "scope": "material",
      "conditions": {
        "form": "A15 Nb3Sn, highest value reported in the literature",
        "reference_year": 1964
      },
      "method": "Value stated in the review, which attributes it to Hanak et al. (1964)",
      "status": "ground",
      "source": "godeke2006",
      "where": "Introduction, first paragraph (sentence beginning 'Its highest reported critical temperature')",
      "source_detail": {
        "title": "A Review of the Properties of Nb3Sn and Their Variation with A15 Composition, Morphology and Strain State",
        "id": "arXiv:cond-mat/0606303",
        "url": "https://arxiv.org/pdf/cond-mat/0606303",
        "year": 2006,
        "kind": "paper",
        "license": "arXiv (author-submitted preprint)"
      }
    },
    {
      "benchmark": "critical_temperature",
      "label": "Critical temperature Tc(0), near-stoichiometric thin film",
      "value": 18,
      "bound": "exact",
      "unit": "K",
      "scope": "material",
      "conditions": {
        "form": "thin film, residual resistivity 9 µΩcm, 24.8 at.% Sn (close to stoichiometric)",
        "temperature": "0 K, extrapolated"
      },
      "method": "Review text says the film has a Tc(0) of close to 18 K; the value is a fitted extrapolation",
      "status": "calculated",
      "source": "godeke2006",
      "where": "Section V, text on the film results with varying resistivity (Hc2(T) of thin films)",
      "source_detail": {
        "title": "A Review of the Properties of Nb3Sn and Their Variation with A15 Composition, Morphology and Strain State",
        "id": "arXiv:cond-mat/0606303",
        "url": "https://arxiv.org/pdf/cond-mat/0606303",
        "year": 2006,
        "kind": "paper",
        "license": "arXiv (author-submitted preprint)"
      }
    },
    {
      "benchmark": "critical_temperature",
      "label": "Critical temperature Tc(0), optimally dirty thin film",
      "value": 16,
      "bound": "exact",
      "unit": "K",
      "scope": "material",
      "conditions": {
        "form": "thin film, residual resistivity 35 µΩcm, 23.6 at.% Sn",
        "temperature": "0 K, extrapolated"
      },
      "method": "Printed as about 16 K in the review's thin-film discussion; extrapolated to 0 K",
      "status": "calculated",
      "source": "godeke2006",
      "where": "Section V, text on the film results with varying resistivity (Hc2(T) of thin films)",
      "source_detail": {
        "title": "A Review of the Properties of Nb3Sn and Their Variation with A15 Composition, Morphology and Strain State",
        "id": "arXiv:cond-mat/0606303",
        "url": "https://arxiv.org/pdf/cond-mat/0606303",
        "year": 2006,
        "kind": "paper",
        "license": "arXiv (author-submitted preprint)"
      }
    },
    {
      "benchmark": "critical_temperature",
      "label": "Critical temperature Tc(0), disordered thin film",
      "value": 10.5,
      "bound": "exact",
      "unit": "K",
      "scope": "material",
      "conditions": {
        "form": "thin film, residual resistivity 70 µΩcm, 21 at.% Sn",
        "temperature": "0 K, extrapolated"
      },
      "method": "Printed as about 10.5 K in the review's thin-film discussion; extrapolated to 0 K",
      "status": "calculated",
      "note": "Shows how strongly Tc falls with tin deficiency and disorder; not a wire value.",
      "source": "godeke2006",
      "where": "Section V, text on the film results with varying resistivity (Hc2(T) of thin films)",
      "source_detail": {
        "title": "A Review of the Properties of Nb3Sn and Their Variation with A15 Composition, Morphology and Strain State",
        "id": "arXiv:cond-mat/0606303",
        "url": "https://arxiv.org/pdf/cond-mat/0606303",
        "year": 2006,
        "kind": "paper",
        "license": "arXiv (author-submitted preprint)"
      }
    },
    {
      "benchmark": "critical_temperature",
      "label": "Critical temperature Tc(0), upper phase boundary for ternary wires",
      "value": 18,
      "bound": "exact",
      "unit": "K",
      "scope": "material",
      "conditions": {
        "form": "ternary wires with the highest tin fraction",
        "temperature": "0 K, extrapolated"
      },
      "method": "Review concludes that the highest Sn fractions in wires represent an upper phase boundary of about 18 K; not a single measured sample",
      "status": "calculated",
      "source": "godeke2006",
      "where": "Section V, paragraph on the upper phase boundary of wires (text beside the Hc2(T) fit)",
      "source_detail": {
        "title": "A Review of the Properties of Nb3Sn and Their Variation with A15 Composition, Morphology and Strain State",
        "id": "arXiv:cond-mat/0606303",
        "url": "https://arxiv.org/pdf/cond-mat/0606303",
        "year": 2006,
        "kind": "paper",
        "license": "arXiv (author-submitted preprint)"
      }
    },
    {
      "benchmark": "upper_critical_field",
      "label": "Upper critical field, upper phase boundary for ternary wires",
      "value": 29,
      "bound": "exact",
      "unit": "T",
      "scope": "material",
      "conditions": {
        "form": "ternary wires with the highest tin fraction",
        "temperature": "0 K, extrapolated"
      },
      "method": "Printed as about 29 T in the review; an extrapolated upper phase boundary rather than a single measured sample",
      "status": "calculated",
      "source": "godeke2006",
      "where": "Section V, paragraph on the upper phase boundary of wires (text beside the Hc2(T) fit)",
      "source_detail": {
        "title": "A Review of the Properties of Nb3Sn and Their Variation with A15 Composition, Morphology and Strain State",
        "id": "arXiv:cond-mat/0606303",
        "url": "https://arxiv.org/pdf/cond-mat/0606303",
        "year": 2006,
        "kind": "paper",
        "license": "arXiv (author-submitted preprint)"
      }
    },
    {
      "benchmark": "upper_critical_field",
      "label": "Upper critical field, near-stoichiometric thin film",
      "value": 26.5,
      "bound": "exact",
      "unit": "T",
      "scope": "material",
      "conditions": {
        "form": "thin film, residual resistivity 9 µΩcm, 24.8 at.% Sn",
        "temperature": "0 K, extrapolated"
      },
      "method": "Printed as about 26.5 T in the review; reduced compared with the disordered film, and extrapolated",
      "status": "calculated",
      "note": "Thin film, not a bulk wire; the review says the near-stoichiometric film has a reduced Hc2(0) at a Tc(0) of close to 18 K.",
      "source": "godeke2006",
      "where": "Section V, text on the film results with varying resistivity (Hc2(T) of thin films)",
      "source_detail": {
        "title": "A Review of the Properties of Nb3Sn and Their Variation with A15 Composition, Morphology and Strain State",
        "id": "arXiv:cond-mat/0606303",
        "url": "https://arxiv.org/pdf/cond-mat/0606303",
        "year": 2006,
        "kind": "paper",
        "license": "arXiv (author-submitted preprint)"
      }
    },
    {
      "benchmark": "upper_critical_field",
      "label": "Upper critical field, optimally dirty thin film",
      "value": 29,
      "bound": "exact",
      "unit": "T",
      "scope": "material",
      "conditions": {
        "form": "thin film, residual resistivity 35 µΩcm, 23.6 at.% Sn",
        "temperature": "0 K, extrapolated"
      },
      "method": "Printed as about 29 T in the review's thin-film discussion; extrapolated",
      "status": "calculated",
      "source": "godeke2006",
      "where": "Section V, text on the film results with varying resistivity (Hc2(T) of thin films)",
      "source_detail": {
        "title": "A Review of the Properties of Nb3Sn and Their Variation with A15 Composition, Morphology and Strain State",
        "id": "arXiv:cond-mat/0606303",
        "url": "https://arxiv.org/pdf/cond-mat/0606303",
        "year": 2006,
        "kind": "paper",
        "license": "arXiv (author-submitted preprint)"
      }
    },
    {
      "benchmark": "upper_critical_field",
      "label": "Upper critical field, disordered thin film",
      "value": 15,
      "bound": "exact",
      "unit": "T",
      "scope": "material",
      "conditions": {
        "form": "thin film, residual resistivity 70 µΩcm, 21 at.% Sn",
        "temperature": "0 K, extrapolated"
      },
      "method": "Printed as about 15 T in the review's thin-film discussion; extrapolated",
      "status": "calculated",
      "source": "godeke2006",
      "where": "Section V, text on the film results with varying resistivity (Hc2(T) of thin films)",
      "source_detail": {
        "title": "A Review of the Properties of Nb3Sn and Their Variation with A15 Composition, Morphology and Strain State",
        "id": "arXiv:cond-mat/0606303",
        "url": "https://arxiv.org/pdf/cond-mat/0606303",
        "year": 2006,
        "kind": "paper",
        "license": "arXiv (author-submitted preprint)"
      }
    },
    {
      "benchmark": "upper_critical_field",
      "label": "Upper critical field of state-of-the-art wire at 4.2 K",
      "value": 24,
      "value_high": 26.5,
      "bound": "range",
      "unit": "T",
      "scope": "material",
      "conditions": {
        "form": "state-of-the-art Ta- and Ti-doped Nb3Sn strands",
        "temperature": "4.2 K"
      },
      "method": "Range printed in the paper's introduction for state-of-the-art doped strands at 4.2 K",
      "status": "ground",
      "source": "prm2024",
      "where": "Abstract, first paragraph (and Introduction, first paragraph)",
      "source_detail": {
        "title": "Influence of Nb alloying on Nb recrystallization and the upper critical field of Nb3Sn",
        "id": "doi:10.1103/PhysRevMaterials.8.084801 (Phys. Rev. Materials 8, 084801, 2024; accepted manuscript on CHORUS)",
        "url": "https://link.aps.org/accepted/10.1103/PhysRevMaterials.8.084801",
        "year": 2024,
        "kind": "paper",
        "license": "accepted manuscript (CHORUS)"
      }
    },
    {
      "benchmark": "lattice_parameter",
      "label": "Lattice parameter of the A15 cell",
      "value": 0.529,
      "bound": "exact",
      "unit": "nm",
      "scope": "material",
      "conditions": {
        "composition": "stoichiometric A15 Nb3Sn"
      },
      "method": "Value printed as about 0.529 nm for the stoichiometric composition in the review",
      "status": "ground",
      "source": "godeke2006",
      "where": "Text on the A15 structure beside figure 2 (next to the Nb-chain distance discussion)",
      "source_detail": {
        "title": "A Review of the Properties of Nb3Sn and Their Variation with A15 Composition, Morphology and Strain State",
        "id": "arXiv:cond-mat/0606303",
        "url": "https://arxiv.org/pdf/cond-mat/0606303",
        "year": 2006,
        "kind": "paper",
        "license": "arXiv (author-submitted preprint)"
      }
    },
    {
      "benchmark": "melting_point",
      "label": "Melting point (supplier product sheet)",
      "value": 2100,
      "bound": "exact",
      "unit": "°C",
      "scope": "material",
      "conditions": {
        "form": "niobium tin powder, supplier product (American Elements, CAS 12035-04-0)"
      },
      "method": "Supplier safety data sheet value; the test method is not stated",
      "status": "ground",
      "note": "Supplier value for a commercial powder; check against a primary reference before use in design.",
      "source": "ae-nb3sn",
      "where": "Section 9.1, row Melting point/Melting range",
      "source_detail": {
        "title": "American Elements: Niobium tin (CAS 12035-04-0), product page with safety data sheet",
        "id": "CAS 12035-04-0; PubChem CID 15251588",
        "url": "https://www.americanelements.com/cas/12035-04-0",
        "year": 2026,
        "kind": "datasheet",
        "license": "supplier document, linked not reproduced"
      }
    },
    {
      "benchmark": "operating_temperature",
      "label": "Cryogenic operating temperature of Nb3Sn magnets",
      "value": 4,
      "bound": "exact",
      "unit": "K",
      "scope": "material",
      "conditions": {
        "coolant": "supercritical helium"
      },
      "method": "ITER describes its Nb3Sn and NbTi magnets as cooled with supercritical helium in the range of 4 Kelvin",
      "status": "ground",
      "source": "iter-magnets",
      "where": "Magnets page, opening paragraph",
      "source_detail": {
        "title": "ITER Superconducting Magnets (ITER Machine Systems)",
        "id": "ITER Organization, Magnets page",
        "url": "https://www.iter.org/machine/magnets",
        "year": 2026,
        "kind": "web",
        "license": "ITER web content, cited not reproduced"
      }
    },
    {
      "benchmark": "a15_tin_range",
      "label": "Tin content range of the A15 phase",
      "value": 18,
      "value_high": 25,
      "bound": "range",
      "unit": "at.% Sn",
      "scope": "material",
      "conditions": {
        "unit_in_source": "beta, atomic fraction of Sn, 0.18 to 0.25"
      },
      "method": "Converted by Space Mushroom from beta = 0.18 to 0.25 (multiplied by 100); the review gives the A15 stability range as 0.18 to 0.25",
      "status": "ground",
      "source": "godeke2006",
      "where": "Introduction, paragraph on the Nb-Sn phase diagram (text beside figure 1)",
      "source_detail": {
        "title": "A Review of the Properties of Nb3Sn and Their Variation with A15 Composition, Morphology and Strain State",
        "id": "arXiv:cond-mat/0606303",
        "url": "https://arxiv.org/pdf/cond-mat/0606303",
        "year": 2006,
        "kind": "paper",
        "license": "arXiv (author-submitted preprint)"
      }
    }
  ],
  "corrosion": [],
  "risks": {
    "hazards": [
      {
        "text": "Supplier SDS classifies the niobium tin powder as a flammable solid (H228) that causes skin irritation (H315), serious eye irritation (H319) and may cause respiratory irritation (H335).",
        "ghs": [
          "H228",
          "H315",
          "H319",
          "H335"
        ],
        "source": "ae-nb3sn",
        "where": "Sections 2.1 and 2.2"
      },
      {
        "text": "In a fire, use special powder for metal fires. Water is listed as an unsuitable extinguishing agent. For transport the supplier gives UN3089, metal powder, flammable, n.o.s. (niobium tin powder), class 4.1, packing group III.",
        "ghs": [],
        "source": "ae-nb3sn",
        "where": "Sections 5.1 and 14"
      },
      {
        "text": "The supplier prints an exposure limit for tin metal, oxide and inorganic compounds as Sn of 2 mg/m3 (USA PEL). The limit is for tin, not for Nb3Sn specifically.",
        "ghs": [],
        "source": "ae-nb3sn",
        "where": "Section 8.1"
      }
    ],
    "failure_risks": [
      {
        "mode": "Cracking of the A15 layer under large strain",
        "trigger": "Large strain in the composite wire, from thermal-contraction differences and Lorentz forces in a magnet",
        "consequence": "Serious and irreversible damage to the superconductor, in the form of cracks in the brittle A15 material",
        "severity": "high",
        "source": "godeke2006",
        "where": "Section on strain effects (text beside figure 11)"
      },
      {
        "mode": "Falling critical current at high field",
        "trigger": "Operation above about 12 to 15 T",
        "consequence": "The critical current density of present Nb3Sn conductors declines swiftly above 12 to 15 T, so higher fields need better vortex pinning (PRM 2024)",
        "severity": "moderate",
        "source": "prm2024",
        "where": "Abstract, first paragraph"
      },
      {
        "mode": "Loss of superconducting performance with tin deficiency",
        "trigger": "A15 phase with about 21 at.% Sn and high residual resistivity (70 µΩcm thin film)",
        "consequence": "Tc(0) falls to about 10.5 K and Hc2(0) to about 15 T in the disordered film, against about 18 K and 26.5 T for the near-stoichiometric film",
        "severity": "moderate",
        "source": "godeke2006",
        "where": "Section V, text on the film results with varying resistivity"
      }
    ],
    "side_effects": [],
    "handling": [
      {
        "text": "Keep containers tightly sealed in a cool, dry, well-ventilated place. Protect against electrostatic charges and store away from oxidising agents.",
        "source": "ae-nb3sn",
        "where": "Section 7.1 and 7.2"
      }
    ],
    "mitigations": []
  },
  "uses": [
    {
      "application": "electronics-and-chips",
      "device": "Toroidal-field and central-solenoid magnets of ITER",
      "example": "ITER's magnets are made of Nb3Sn or NbTi superconductors; the toroidal-field coils reach a maximum field of 11.8 T and the central solenoid a maximum field of 13 T. Nb3Sn strand for these systems was produced by nine suppliers, 500 metric tonnes of strand in a procurement that ran from 2008 to 2015.",
      "source": "iter-magnets",
      "where": "Magnets page, Toroidal Field System, Central Solenoid, and the paragraph on strand procurement"
    },
    {
      "application": "electronics-and-chips",
      "device": "Quadrupole magnets for the High-Luminosity LHC at CERN",
      "example": "CERN Courier reports that Nb3Sn will allow the HL-LHC quadrupole magnets to reach fields as high as 11.5 T.",
      "source": "cern-courier-2025",
      "where": "Article body, paragraph on Nb3Sn magnet fields (dated 24 March 2025)"
    }
  ],
  "supply": [
    {
      "subject": "Niobium",
      "producers": [
        {
          "country": "Brazil",
          "share_percent": 92.9,
          "year": 2025
        },
        {
          "country": "Canada",
          "share_percent": 5.4,
          "year": 2025
        },
        {
          "country": "Russia",
          "share_percent": 0.3,
          "year": 2025
        },
        {
          "country": "Congo (Kinshasa)",
          "share_percent": 0.9,
          "year": 2025
        }
      ],
      "critical_lists": [
        {
          "list": "USGS 2025 List of Critical Minerals (entry 'Niobium, used to strengthen steel')",
          "listed": true
        },
        {
          "list": "EU critical raw materials list (entry 'Niobium')",
          "listed": true
        }
      ],
      "recycling": "USGS: niobium was recycled when niobium-bearing steels and superalloys were recycled; scrap recovery for niobium content was negligible, and total recycling may have been as much as 20% of apparent consumption.",
      "substitutes": [
        "USGS: ceramic matrix composites, molybdenum, tantalum and tungsten can replace niobium in high-temperature superalloys, with a performance loss or higher cost. For superconducting wire, NbTi is the present workhorse (godeke2006), and Nb3Sn is the higher-field alternative."
      ],
      "source": "usgs-mcs2026-niobium",
      "where": "World Mine Production and Reserves table, 2025e (world total 112,000 t; shares calculated by Space Mushroom from the table: Brazil 104,000 t, Canada 6,000 t, Russia 300 t, Congo (Kinshasa) 970 t). Recycling and Substitutes sections."
    },
    {
      "subject": "Tin",
      "producers": [
        {
          "country": "China",
          "share_percent": 24.5,
          "year": 2025
        },
        {
          "country": "Indonesia",
          "share_percent": 21,
          "year": 2025
        },
        {
          "country": "Peru",
          "share_percent": 11.4,
          "year": 2025
        },
        {
          "country": "Brazil",
          "share_percent": 9.7,
          "year": 2025
        },
        {
          "country": "Bolivia",
          "share_percent": 5.2,
          "year": 2025
        }
      ],
      "critical_lists": [
        {
          "list": "USGS 2025 List of Critical Minerals (entry 'Tin, used for food and beverage cans, circuit board components and corrosion-resistant metal coatings')",
          "listed": true
        },
        {
          "list": "EU critical raw materials list (tin is not on the list)",
          "listed": false
        }
      ],
      "recycling": "USGS tin chapter: about 17,000 tons of tin from old and new scrap was estimated to have been recycled in 2025.",
      "substitutes": [],
      "source": "usgs-mcs2026-tin",
      "where": "World Mine Production and Reserves table, 2025e (world total 290,000 t; shares calculated by Space Mushroom from the table: China 71,000 t, Indonesia 61,000 t, Peru 33,000 t, Brazil 28,000 t, Bolivia 15,000 t). Recycling section."
    }
  ],
  "media": [],
  "documents": [
    {
      "title": "American Elements: Niobium tin (CAS 12035-04-0), safety data sheet and product page",
      "type": "sds",
      "url": "https://www.americanelements.com/cas/12035-04-0",
      "year": 2026
    },
    {
      "title": "A Review of the Properties of Nb3Sn and Their Variation with A15 Composition, Morphology and Strain State (arXiv:cond-mat/0606303)",
      "type": "paper",
      "url": "https://arxiv.org/pdf/cond-mat/0606303",
      "year": 2006
    },
    {
      "title": "Influence of Nb alloying on Nb recrystallization and the upper critical field of Nb3Sn (accepted manuscript, Phys. Rev. Materials 8, 084801)",
      "type": "paper",
      "url": "https://link.aps.org/accepted/10.1103/PhysRevMaterials.8.084801",
      "year": 2024
    },
    {
      "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: Tin",
      "type": "report",
      "url": "https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-tin.pdf",
      "year": 2026
    }
  ],
  "gaps": [
    "Density of Nb3Sn not found: the supplier sheet prints 'No data available' and no other fetched source gives a value.",
    "No corrosion or oxidation-in-air data for Nb3Sn wire found. The searches turned up internal oxidation of Nb-Ta-Hf alloys used on purpose, and HF-based removal of the Ta barrier during processing, neither of which is an environmental corrosion result. The corrosion list is therefore empty.",
    "No critical-current density (Jc) number at a stated field and temperature was read in a fetched page; the review's Jc results are in figures only. The Jc statement in this profile comes from the 2024 paper's qualitative sentence.",
    "Wire heat-treatment (reaction) temperature and time were not read from a fetched page, so the process route is not described in the recipe line.",
    "No UNS, EN, DIN, JIS or ASTM designation for the Nb3Sn compound was found in a fetched source. The supplier lists CAS 12035-04-0 and PubChem CID 15251588.",
    "Non-canonical property names used because property-canon.yaml has no entry for them: critical_temperature, upper_critical_field, lattice_parameter, operating_temperature and a15_tin_range.",
    "Space application not found. The applications list has no magnets, fusion or accelerator category, so the ITER and HL-LHC uses are filed under electronics-and-chips as the nearest available tag. Please review that choice.",
    "Upper critical field values at 0 K are extrapolations from the review's fits, and the 29 T upper boundary is for ternary wires, not a single sample.",
    "Hf-alloying results (about 28 T and about 31 T, from the 2024 paper) are described there as so-far observations and are left out of the property rows.",
    "Creep, fatigue and thermal-expansion data for Nb3Sn were not searched for in this run.",
    "No image fetched, so the media list is empty."
  ],
  "story": {
    "why": "Niobium-tin is an A15 intermetallic superconductor. Superconductivity was found shortly after that of V3Si, the first A15 superconductor. Its interest is that it carries very large current densities at fields beyond the reach of NbTi, which is the usual workhorse for large superconducting magnets. The trade is brittleness: the A15 layer is hard and cracks under large strain, so the wire has to be handled and supported with care.",
    "uses": [
      {
        "where": "Fusion magnets (ITER)",
        "line": "ITER's toroidal-field coils reach a maximum field of 11.8 T and its central solenoid 13 T. The magnets are wound from Nb3Sn cable and NbTi, and they are cooled to about 4 K with supercritical helium."
      },
      {
        "where": "Accelerator magnets (HL-LHC)",
        "line": "CERN reports that Nb3Sn lets the High-Luminosity LHC quadrupoles reach fields as high as 11.5 T, compared with the current LHC design."
      }
    ],
    "can_do": [
      {
        "label": "Field",
        "line": "State-of-the-art Ta- and Ti-doped strands reach an upper critical field of about 24 to 26.5 T at 4.2 K. Extrapolated to 0 K, the highest-tin ternary wires reach about 29 T.",
        "benchmark": "upper_critical_field",
        "scope": "material"
      },
      {
        "label": "Temperature",
        "line": "The highest critical temperature reported is 18.3 K. A near-stoichiometric thin film has a Tc(0) of close to 18 K.",
        "benchmark": "critical_temperature",
        "scope": "material"
      },
      {
        "label": "Cryogenic operation",
        "line": "ITER cools its Nb3Sn and NbTi magnets with supercritical helium at about 4 K.",
        "scope": "material",
        "value": "4 K"
      }
    ],
    "compare": "Nb3Sn carries very large current densities at fields far beyond the limits of NbTi, the commonly used superconductor for large magnets, and it is the material used for ITER's highest-field coils. The price is brittleness: large strain cracks the A15 layer. Its highest reported critical temperature of 18.3 K is above the 16 K and 10.5 K that the review gives for disordered thin films.",
    "compare_rows": [
      {
        "label": "Highest critical temperature",
        "benchmark": "critical_temperature",
        "scope": "material"
      },
      {
        "label": "Upper critical field at 4.2 K",
        "benchmark": "upper_critical_field",
        "scope": "material"
      },
      {
        "label": "Melting point (supplier)",
        "benchmark": "melting_point",
        "scope": "material"
      }
    ],
    "handling": [
      "Keep it dry, closed and away from oxidising agents, and protect it from electrostatic charge.",
      "Use a special powder for metal fires and do not use water on a fire.",
      "Limit strain in the wire. Large strain cracks the A15 layer, and that damage is irreversible."
    ],
    "good_for": [
      "High-field magnets at 4 K. ITER's central solenoid is designed for a maximum field of 13 T.",
      "High critical temperature for a superconductor: 18.3 K is the highest reported for Nb3Sn."
    ],
    "watch_out": [
      "Brittleness. Large strain cracks the A15 layer irreversibly.",
      "Critical current falls off swiftly above about 12 to 15 T for present conductors.",
      "Tin deficiency and disorder lower Tc and Hc2 sharply in thin films."
    ],
    "verdict": "Nb3Sn is the superconductor chosen for ITER's highest-field coils and for the HL-LHC quadrupoles. It is brittle and must be kept free of large strain, and the sources read here do not answer its corrosion or oxidation behaviour in air.",
    "recipe": {
      "line": "Nb3Sn is a binary intermetallic compound: three niobium atoms for each tin atom, with the tin on a body-centred cubic sublattice and the niobium in chains. The review notes that the A15 phase forms by solid-state diffusion reactions between niobium and tin.",
      "parts": [
        {
          "name": "Niobium",
          "symbol": "Nb",
          "role": "Forms chains of niobium atoms. The review links the short Nb to Nb spacing in these chains to the high critical temperature."
        },
        {
          "name": "Tin",
          "symbol": "Sn",
          "role": "Sits on the body-centred sublattice. The tin fraction controls Tc and Hc2: both fall as the A15 phase becomes tin-deficient."
        }
      ]
    },
    "risk_groups": [
      {
        "title": "For people",
        "lead": "The supplier classes the fine powder as a flammable solid and irritant, and says the acute and chronic toxicity of the substance is not fully known.",
        "points": [
          {
            "label": "The powder",
            "line": "The supplier classifies the powder as a flammable solid (H228) that causes skin irritation, serious eye irritation and respiratory irritation (H315, H319, H335)."
          },
          {
            "label": "In a fire",
            "line": "The supplier advises a special powder for metal fires and says water is unsuitable."
          },
          {
            "label": "Tin exposure",
            "line": "The supplier prints a USA exposure limit of 2 mg/m3 for tin compounds, measured as Sn."
          }
        ],
        "level": 0,
        "verdict": "Flammable fine powder; the supplier sheet classes the…"
      },
      {
        "title": "In operation",
        "points": [
          {
            "label": "Strain",
            "line": "A wire that is strained too far is damaged irreversibly, because the A15 layer cracks. Strain comes from thermal contraction differences and magnetic forces in a magnet."
          },
          {
            "label": "High field",
            "line": "The critical current of present Nb3Sn conductors falls off swiftly above about 12 to 15 T."
          }
        ]
      },
      {
        "title": "Handling and storage",
        "points": [
          {
            "label": "Storage",
            "line": "Keep containers tightly sealed in a cool, dry, well-ventilated place, away from oxidising agents and protected from electrostatic charge."
          },
          {
            "label": "Transport",
            "line": "The supplier gives the transport class as flammable solid, UN3089, packing group III."
          }
        ]
      }
    ]
  },
  "updated": "2026-10-26",
  "review": {
    "status": "draft",
    "method": "assistant",
    "checked_values": 14,
    "unreachable": 1,
    "caveats": 3,
    "note": "Read by an AI assistant on 2026-10-26. verify-values found 13 of 14 values in their cited source text; the melting point (2100 °C) is on a JavaScript-rendered supplier page that the script cannot read, and was checked by reading the page in a browser in this run. Supply shares are calculated from the USGS production tables. Corrosion, density and Jc are left as gaps."
  },
  "sources": {
    "godeke2006": {
      "title": "A Review of the Properties of Nb3Sn and Their Variation with A15 Composition, Morphology and Strain State",
      "id": "arXiv:cond-mat/0606303",
      "url": "https://arxiv.org/pdf/cond-mat/0606303",
      "year": 2006,
      "kind": "paper",
      "license": "arXiv (author-submitted preprint)"
    },
    "prm2024": {
      "title": "Influence of Nb alloying on Nb recrystallization and the upper critical field of Nb3Sn",
      "id": "doi:10.1103/PhysRevMaterials.8.084801 (Phys. Rev. Materials 8, 084801, 2024; accepted manuscript on CHORUS)",
      "url": "https://link.aps.org/accepted/10.1103/PhysRevMaterials.8.084801",
      "year": 2024,
      "kind": "paper",
      "license": "accepted manuscript (CHORUS)"
    },
    "ae-nb3sn": {
      "title": "American Elements: Niobium tin (CAS 12035-04-0), product page with safety data sheet",
      "id": "CAS 12035-04-0; PubChem CID 15251588",
      "url": "https://www.americanelements.com/cas/12035-04-0",
      "year": 2026,
      "kind": "datasheet",
      "license": "supplier document, linked not reproduced"
    },
    "iter-magnets": {
      "title": "ITER Superconducting Magnets (ITER Machine Systems)",
      "id": "ITER Organization, Magnets page",
      "url": "https://www.iter.org/machine/magnets",
      "year": 2026,
      "kind": "web",
      "license": "ITER web content, cited not reproduced"
    },
    "cern-courier-2025": {
      "title": "CERN gears up for tighter focusing (CERN Courier, 24 March 2025)",
      "id": "CERN Courier article",
      "url": "https://cerncourier.com/a/cern-gears-up-for-tighter-focusing/",
      "year": 2025,
      "kind": "web",
      "license": "CERN Courier, cited not reproduced"
    },
    "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-tin": {
      "title": "Mineral Commodity Summaries 2026, Tin",
      "id": "USGS MCS 2026, February 2026",
      "url": "https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-tin.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)"
    },
    "ec-crm": {
      "title": "Critical raw materials (European Commission, fifth list of 34 critical raw materials)",
      "id": "EU critical raw materials list",
      "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",
  "url": "https://spacemushroom.com/profiles/nb3sn/"
}