spore: profile
id: tellurium
spore_version: 0.2
family: semiconductor-materials
name: Tellurium
abbreviation: Te
role: metalloid, semiconductor compound element and alloy additive
category: metals
type: heavy-metals
summary: |
  Tellurium (Te, atomic number 52) is a brittle, silver-white metalloid (Wikipedia). Its main uses are cadmium telluride (CdTe) thin-film solar panels, which the USGS puts at 70% of 2025 global tellurium end use, and bismuth telluride thermoelectric devices at 15%. Most tellurium is recovered from the anode slimes of copper refining, and the USGS says China produced 80% of refined tellurium in 2025. The one space-related source read here is a laboratory proton test of CdTe cells on cerium-doped space cover glass, not an orbital result for tellurium itself.
best_for: CdTe thin-film solar cells and bismuth telluride thermoelectric devices, the two largest uses (USGS)
weakest_at: 'Supply and toxicity: most of it is a copper by-product, China leads refined output, and the element is toxic if swallowed'
identity:
  formula: Te, elemental tellurium
  cas: 13494-80-9
  source: pubchem-te
  where: Names and Identifiers (CAS 13494-80-9); Molecular Weight 127.6
tags:
  environments: []
  stresses: []
  applications:
    - solar-arrays
    - thermal-control
    - optics-and-cameras
    - structures
properties:
  - benchmark: density
    label: Density of solid
    value: 6240
    unit: kg/m3
    scope: material
    conditions:
      basis: temperature not stated on the page
    method: Value printed on WebElements as 6240 kg m-3 (unit kept as printed; converts to 6.24 g/cm3 on import)
    status: ground
    source: we-phys
    where: Density properties, Density of solid row
  - benchmark: density
    label: Density (range in PubChem record)
    value: 6
    value_high: 6.25
    bound: range
    unit: g/cm3
    scope: material
    conditions:
      basis: range as printed in PubChem's physical property entries; temperature not stated
    method: Range printed on the PubChem record
    status: ground
    source: pubchem-te
    where: Chemical and Physical Properties, Density entry (6.0-6.25 g/cm3)
  - benchmark: melting_point
    label: Melting point (PubChem)
    value: 449.5
    unit: °C
    scope: material
    conditions:
      basis: melting point as printed, no pressure stated
    method: Value printed on the PubChem record
    status: ground
    source: pubchem-te
    where: Chemical and Physical Properties, Melting Point entry (449.5 °C)
  - benchmark: melting_point
    label: Melting point (SDS)
    value: 449.8
    unit: °C
    scope: material
    conditions:
      basis: melting point/freezing point as printed on the supplier SDS, product Te powder
    method: Value printed in the supplier SDS, parenthesis after the Fahrenheit value
    status: ground
    source: materion-sds
    where: Section 9, Melting point/freezing point row (841.64 F (449.8 C))
  - benchmark: boiling_point
    label: Boiling point (PubChem)
    value: 988
    unit: °C
    scope: material
    conditions:
      pressure: 760 mmHg, as printed
    method: Value printed on the PubChem record
    status: ground
    source: pubchem-te
    where: Chemical and Physical Properties, Boiling Point entry (988 °C @760 mm Hg)
  - benchmark: boiling_point
    label: Boiling point (SDS)
    value: 989.9
    unit: °C
    scope: material
    conditions:
      basis: initial boiling point and boiling range as printed on the supplier SDS
    method: Value printed in the supplier SDS, parenthesis after the Fahrenheit value
    status: ground
    source: materion-sds
    where: Section 9, Initial boiling point and boiling range row (1813.82 F (989.9 C))
  - benchmark: elastic_modulus
    label: Young's modulus
    value: 43
    unit: GPa
    scope: material
    conditions:
      basis: temperature not stated on the page
    method: Value printed on WebElements
    status: ground
    source: we-phys
    where: Elastic properties, Young's modulus row
  - benchmark: shear_modulus
    label: Rigidity (shear) modulus
    value: 16
    unit: GPa
    scope: material
    conditions:
      basis: temperature not stated on the page
    method: Value printed on WebElements, which calls the shear modulus the rigidity modulus
    status: ground
    source: we-phys
    where: Elastic properties, Rigidity modulus row
  - benchmark: bulk_modulus
    label: Bulk modulus
    value: 65
    unit: GPa
    scope: material
    conditions:
      basis: temperature not stated on the page
    method: Value printed on WebElements
    status: ground
    source: we-phys
    where: Elastic properties, Bulk modulus row
  - benchmark: thermal_conductivity
    label: Thermal conductivity
    value: 3
    unit: W/(m·K)
    scope: material
    conditions:
      basis: temperature not stated on the page
    method: Value printed on WebElements as 3 W m-1 K-1
    status: ground
    source: we-phys
    where: Heat and conduction, Thermal conductivity row
  - benchmark: mineral_hardness
    label: Mineral hardness
    value: 2.25
    unit: '-'
    scope: material
    conditions:
      basis: WebElements prints no units for this value
    method: Value printed on WebElements as 2.25 (no units)
    status: ground
    note: Non-canonical name (not in property-canon.yaml); WebElements gives no unit, so the unit is '-'.
    source: we-phys
    where: Hardnesses, Mineral hardness row
  - benchmark: brinell_hardness
    label: Brinell hardness
    value: 180
    unit: MN m-2
    scope: material
    conditions:
      basis: test load and sample form not stated on the page
    method: Value printed on WebElements as 180 MN m-2
    status: ground
    note: Non-canonical name (not in property-canon.yaml).
    source: we-phys
    where: Hardnesses, Brinell hardness row
  - benchmark: speed_of_sound
    label: Velocity of sound
    value: 2610
    unit: m/s
    scope: material
    conditions:
      basis: temperature and direction not stated on the page
    method: Value printed on WebElements as 2610 m s-1
    status: ground
    note: Non-canonical name (not in property-canon.yaml).
    source: we-phys
    where: Acoustic properties, Velocity of sound row
corrosion:
  - environment: Air, heated to burning
    headline: Tellurium burns in air to form tellurium dioxide.
    effect: WebElements says tellurium burns in air to form the dioxide, TeO2, written as Te(s) + 2O2(g) giving TeO2(s). No ignition temperature or rate is given.
    rating: moderate
    conditions:
      basis: rating is the assistant's reading of the reaction; the source gives no temperature or rate
    source: we-chem
    where: Reaction of tellurium with air
  - environment: Water
    headline: Tellurium does not react with water under normal conditions.
    effect: WebElements reports no reaction with water under normal conditions. The supplier SDS lists solubility in water as insoluble.
    rating: none
    conditions:
      basis: rating is the assistant's reading of the wording; the solubility statement is from the SDS
    source: we-chem
    where: Reaction of tellurium with water
  - environment: Dilute non-oxidizing acids
    headline: Tellurium does not react with dilute non-oxidizing acids.
    effect: WebElements says tellurium does not react with dilute non-oxidizing acids. Concentrated or oxidizing acids are not covered in the text read.
    rating: none
    conditions:
      basis: rating is the assistant's reading; only dilute non-oxidizing acids are covered
    source: we-chem
    where: Reaction of tellurium with acids
  - environment: Dilute bases
    headline: Tellurium does not react with dilute bases under normal conditions.
    effect: WebElements says tellurium does not react with dilute bases under normal conditions.
    rating: none
    conditions:
      basis: rating is the assistant's reading; normal conditions only
    source: we-chem
    where: Reaction of tellurium with bases
  - environment: Halogens (fluorine, chlorine, bromine, iodine)
    headline: Fluorine burns tellurium; the other halogens react under controlled conditions.
    effect: WebElements says tellurium reacts with fluorine and burns to form TeF6, and reacts with chlorine, bromine and iodine under controlled conditions, with iodine needing heat, to give tetrahalides. The supplier SDS lists strong oxidizing agents and chlorine as incompatible.
    rating: severe
    conditions:
      basis: rating is the assistant's reading of pure-halogen reactions; no rates given
    source: we-chem
    where: Reaction of tellurium with the halogens
risks:
  hazards:
    - text: PubChem's ECHA aggregate for tellurium uses the signal word Danger. Hazard codes above 10% of 527 company reports are H301 (18.6%), H317 (45.7%), H319 (37.6%), H332 (61.3%), H335 (37.4%), H360 (22.6%), H360Df (39.5%) and H362 (43.8%). Only 4 of 527 reports say the GHS criteria are not met.
      ghs:
        - 'H301: Toxic if swallowed'
        - 'H332: Harmful if inhaled'
        - 'H317: May cause an allergic skin reaction'
        - 'H360Df: May damage the unborn child; suspected of damaging fertility'
        - 'H362: May cause harm to breast-fed children'
      source: pubchem-te
      where: Safety and Hazards, Hazards Identification, GHS Classification (ECHA C&L summary)
    - text: 'The supplier SDS for tellurium powder classes it as a flammable solid, Category 1, and as acutely toxic if swallowed, Category 3. Signal word Danger. Hazard statements: Flammable solid. Toxic if swallowed.'
      ghs: []
      source: materion-sds
      where: Section 2, Hazard(s) identification
    - text: 'Oral LD50 as printed in the SDS: 83 mg/kg in rats, 67 mg/kg in rabbits and 45 mg/kg in guinea pigs.'
      ghs: []
      source: materion-sds
      where: Section 11, Acute toxicity, Oral LD50 rows
    - text: 'Occupational exposure limits printed in the SDS: OSHA PEL 0.1 mg/m3 (Table Z-1, 29 CFR 1910.1000), ACGIH TWA 0.1 mg/m3 and NIOSH TWA 0.1 mg/m3.'
      ghs: []
      source: materion-sds
      where: Section 8, Occupational exposure limits
    - text: PubChem's aggregate includes H360 and H362 (reproductive toxicity) notifications, while the supplier SDS says reproductive or developmental effects are not expected. The two sources disagree; check the SDS for the form handled.
      ghs: []
      source: pubchem-te
      where: Safety and Hazards, GHS Classification; compare Section 11 of the SDS
  failure_risks:
    - mode: Fire of tellurium powder or dust
      trigger: Heat, sparks, open flame or dust accumulation; the SDS classes the solid as a flammable solid, Category 1
      consequence: During a fire, gases hazardous to health may be formed (SDS). PubChem says heating to decomposition gives toxic fumes of tellurium.
      severity: moderate
      source: materion-sds
      where: Section 5, Specific hazards arising from the chemical; Section 2
    - mode: Supply interruption from China
      trigger: 'China''s export licensing from February 2025: end-user documents, a 45-day typical licence and a new licence for any change of use'
      consequence: The USGS reports the annual average European price rose 84% to an estimated $150 per kg in 2025, and the US warehouse price rose 60% to $120 per kg. Restrictions limited European supply.
      severity: high
      source: usgs-te-2026
      where: Events, Trends, and Issues; Salient Statistics, Price rows
    - mode: Supply tied to copper refining
      trigger: More than 90% of tellurium is produced from copper anode slimes, a by-product of electrolytic copper refining
      consequence: Output follows copper refining rates. The USGS says recovery from US copper anode slimes was estimated to have decreased in 2025 from 2024.
      severity: moderate
      source: usgs-te-2026
      where: World Resources; Events, Trends, and Issues
  side_effects:
    - text: When heated to decomposition, tellurium emits toxic fumes of tellurium (PubChem).
      affects: Workers and anyone near a fire or a heated batch
      source: pubchem-te
      where: Chemical and Physical Properties, Decomposition
  handling:
    - text: Minimize dust generation and accumulation. Avoid prolonged exposure. Do not handle, store or open near an open flame. Keep away from heat and sparks, and ground and bond containers and equipment.
      source: materion-sds
      where: Section 7, Precautions for safe handling
    - text: Store locked up in a cool, dry place out of direct sunlight, in a well-ventilated area and away from incompatible materials, which the SDS names as strong oxidizing agents and chlorine.
      source: materion-sds
      where: Section 7, Conditions for safe storage; Section 10, Incompatible materials
    - text: Wear eye protection. Use a NIOSH or MSHA approved respirator where there is a risk of exposure to dust above the exposure limit. Wash thoroughly after handling.
      source: materion-sds
      where: Section 8, Eye/face protection and Respiratory protection; Section 7
  mitigations:
    - text: Keep airborne dust at or below the 0.1 mg/m3 limit printed in the SDS, using general and local exhaust ventilation where dust forms.
      source: materion-sds
      where: Section 7, Precautions for safe handling; Section 8
uses:
  - application: solar-arrays
    device: Cadmium telluride (CdTe) thin-film solar panels
    example: The USGS says tellurium was used predominantly for CdTe thin-film solar cells, and estimates solar power cells took 70% of global tellurium end use in 2025.
    source: usgs-te-2026
    where: Domestic Production and Use, second paragraph (2025 end-use estimates)
  - application: solar-arrays
    device: CdTe thin-film cells on cerium-doped space cover glass (laboratory proton test)
    example: At the lowest proton fluence, 1 x 10^12 per cm2, the relative efficiency was 95%. At 1 x 10^13 per cm2 the mean efficiency dropped by 18%. These were laboratory tests, not flight results.
    source: lamb-2017-cdte
    where: Results, proton fluence series (text on the efficiency at each fluence)
  - application: thermal-control
    device: Bismuth telluride thermoelectric coolers and generators
    example: Witting et al. say bismuth telluride, as alloys with Sb2Te3 for p-type and Bi2Se3 for n-type material, has the highest thermoelectric figure of merit zT of any material around room temperature. The USGS puts thermoelectric devices at 15% of 2025 tellurium end use.
    source: witting-2019
    where: Abstract; the USGS end-use estimate is in Domestic Production and Use
  - application: optics-and-cameras
    device: Thermal-imaging devices and photodetectors
    example: The USGS lists thermal-imaging devices and photodetectors among the uses of tellurium.
    source: usgs-te-2026
    where: Domestic Production and Use, second paragraph
  - application: structures
    device: Free-machining steel and copper alloys
    example: The USGS says tellurium is added to steel to improve machining, and as a minor additive in copper alloys to improve machinability without reducing conductivity.
    source: usgs-te-2026
    where: Domestic Production and Use, second paragraph
supply:
  - subject: Tellurium
    abundance: 0.001 ppm crustal abundance (USGS Professional Paper 1802-A, Table A1, citing Jefferson Science Associates 2014)
    producers:
      - country: China
        share_percent: 80
        year: 2025
    critical_lists:
      - list: 'USGS 2025 List of Critical Minerals (entry: used in solar cells, to strengthen steel and copper, rubber, microchips and laser diodes)'
        listed: true
      - list: EU critical raw materials list (checked on the European Commission overview page; tellurium not among the names on that page)
        listed: false
    us_position: 'US imports for consumption were 6 t in 2024 and an estimated 14 t in 2025 (tellurium content). Import sources 2021 to 2024: Canada 64%, Philippines 14%, Japan 8%, Germany 5%. Net import reliance was above 25% in 2025e. The USGS says China was the leading producer of refined tellurium in 2025, with 80% of estimated global production.'
    recycling: 'USGS: tellurium was recycled from CdTe solar cells in the United States, but the quantity was limited because most of those cells had not reached the end of their useful life.'
    substitutes:
      - 'USGS: amorphous silicon and copper indium gallium diselenide compete with CdTe; bismuth selenide and organic polymers can substitute for bismuth telluride; bismuth, calcium, lead, phosphorus, selenium and sulfur can replace tellurium in many free-machining steels.'
    source: usgs-te-2026
    where: Import Sources (2021 to 2024); Salient Statistics; World Refinery Production; Events, Trends, and Issues; Recycling; Substitutes
media: []
documents:
  - title: USGS Mineral Commodity Summaries 2026, Tellurium
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-tellurium.pdf
    year: 2026
  - title: 'PubChem record for elemental tellurium (CID 6327182): physical properties and GHS classification'
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/compound/Tellurium
    year: 2026
  - title: Materion Advanced Chemicals, Safety Data Sheet T-MSDS0063, Tellurium (Te), issue 08-05-2015
    type: sds
    url: https://www.physics.purdue.edu/primelab/safety/MSDS/SDS/tellurium%20powder%20%20-%20Materion.pdf
    year: 2015
  - title: 'NIST Atomic Weights and Isotopic Compositions: tellurium'
    type: database
    url: https://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl?ele=Te
    year: 2026
  - title: Lamb et al., Proton irradiation of CdTe thin film photovoltaics deposited on cerium-doped space glass, Progress in Photovoltaics (author version, Swansea Cronfa)
    type: paper
    url: https://doi.org/10.1002/pip.2923
    year: 2017
  - title: Witting et al., The Thermoelectric Properties of Bismuth Telluride, Advanced Electronic Materials 2019, 1800904
    type: paper
    url: https://research.dial.uclouvain.be/entities/publication/dbd02e2f-c485-40a6-b684-7aac5b10fc79
    year: 2019
  - title: USGS Professional Paper 1802-A, Critical Mineral Resources of the United States, Table A1 (crustal abundances)
    type: report
    url: https://pubs.usgs.gov/pp/1802/a/pp1802a.pdf
    year: 2017
gaps:
  - No flight, vacuum or radiation result for elemental tellurium was found. The Lamb et al. paper is a laboratory proton test of CdTe cells, and the in-orbit CdTe papers were not read in this run.
  - 'Electrical resistivity: WebElements prints ''about 10000 x 10-8 ohm m'' as an approximate figure with no clear unit form, so it is left out.'
  - Band gap, carrier mobility and other semiconductor values for elemental tellurium were not found in the sources read here.
  - 'Crystal structure and lattice parameters of elemental tellurium: not read in this run.'
  - 'Refractive index (WebElements prints 1.000991 with no clear basis) and reflectivity (50%) are left out: neither has a stated wavelength or basis, and reflectivity has no canonical name.'
  - 'Poisson''s ratio: WebElements prints no data.'
  - 'Non-canonical property names used: mineral_hardness, brinell_hardness, speed_of_sound. A canonical name was not found for these.'
  - Acid and alkali corrosion are qualitative (WebElements). No corrosion rate or concentration was found for concentrated or oxidising acids.
  - The supplier SDS (Materion, issue date 2015) is one manufacturer's document. The PubChem aggregate and the SDS disagree on reproductive toxicity, and no other SDS was checked.
  - 'NIOSH Pocket Guide page for tellurium: the CDC page returned access denied in this run, so the NIOSH 0.1 mg/m3 limit is taken from the SDS, which cites the Pocket Guide. The OSHA Table Z-1 page was not opened directly.'
  - The Witting et al. review was read for its abstract and qualitative statements only; no numeric Bi2Te3 values were taken from it.
  - 'EU critical raw materials list: checked on the European Commission overview page only, not against the Regulation text.'
  - The USGS 2025 critical-minerals entry for tellurium was read through a page summary, not the raw page text.
  - 'Production share for countries other than China: the USGS table is partly garbled in the PDF text, so only China''s 80% share (printed in the text) is entered.'
  - Abundance is the 2014 Jefferson Science Associates figure cited in USGS PP 1802-A; the value is 0.001 ppm as printed.
sources:
  we-phys:
    title: 'WebElements, Tellurium: physical properties (Te, 52)'
    url: https://www.webelements.com/tellurium/physics.html
    kind: web
    license: page content, cited as published
  we-chem:
    title: 'WebElements, Tellurium: reactions of elements (air, water, halogens, acids, bases)'
    url: https://www.webelements.com/tellurium/chemistry.html
    kind: web
    license: page content, cited as published
  pubchem-te:
    title: 'PubChem, Tellurium (CID 6327182): physical properties, decomposition, GHS classification'
    url: https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/6327182/JSON
    kind: database
    license: public domain (NCBI), cited as published
  materion-sds:
    title: Materion Advanced Chemicals, Safety Data Sheet, Tellurium (Te), SDS T-MSDS0063, issue 08-05-2015
    url: https://www.physics.purdue.edu/primelab/safety/MSDS/SDS/tellurium%20powder%20%20-%20Materion.pdf
    kind: datasheet
    license: supplier document, linked not reproduced
  usgs-te-2026:
    title: USGS Mineral Commodity Summaries 2026, Tellurium (February 2026)
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-tellurium.pdf
    kind: report
    license: public domain (USGS)
  usgs-pp1802a:
    title: USGS Professional Paper 1802-A, Critical Mineral Resources of the United States, Table A1
    url: https://pubs.usgs.gov/pp/1802/a/pp1802a.pdf
    kind: report
    license: public domain (USGS)
  usgs-crit-2025:
    title: USGS, About the 2025 List of Critical Minerals
    url: https://www.usgs.gov/programs/mineral-resources-program/science/about-2025-list-critical-minerals
    kind: web
    license: public domain (USGS)
  ec-crm:
    title: European Commission, Critical raw materials (overview page)
    url: https://single-market-economy.ec.europa.eu/sectors/raw-materials/areas-specific-interest/critical-raw-materials_en
    kind: web
    license: European Commission web page
  nist-te:
    title: 'NIST, Atomic Weights and Isotopic Compositions for All Elements: tellurium'
    url: https://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl?ele=Te
    kind: database
    license: public domain (NIST)
  wiki-te:
    title: Wikipedia, Tellurium (used for composition and history only)
    url: https://en.wikipedia.org/wiki/Tellurium
    kind: web
    license: CC BY-SA 4.0
  witting-2019:
    title: Witting et al., The Thermoelectric Properties of Bismuth Telluride, Advanced Electronic Materials 2019, 1800904
    url: https://research.dial.uclouvain.be/entities/publication/dbd02e2f-c485-40a6-b684-7aac5b10fc79
    kind: paper
    license: repository record, cited as published
  lamb-2017-cdte:
    title: Lamb et al., Proton irradiation of CdTe thin film photovoltaics deposited on cerium-doped space glass, Progress in Photovoltaics (2017), doi 10.1002/pip.2923
    url: https://doi.org/10.1002/pip.2923
    kind: paper
    license: author-produced version from Swansea University Cronfa repository (https://cronfa.swan.ac.uk/Record/cronfa34616)
license: CC-BY-4.0
checked_values: 13
updated: '2026-10-26'
review:
  status: draft
  method: assistant
  checked_values: 13
  note: Written by an AI assistant on 2026-10-26 from pages read in this run. Not yet re-checked by a second reader.
story:
  risk_groups:
    - title: For people
      lead: Tellurium is toxic if swallowed. PubChem's aggregate of company reports mixes hazard codes with a reproductive-toxicity signal, so check the supplier SDS for the form handled.
      level: 1
      verdict: Toxic if swallowed; reproductive effects disputed
      points:
        - label: Hazard class
          line: Materion's SDS classes the powder as a flammable solid, Category 1, and as acutely toxic if swallowed, Category 3. The oral LD50 is 83 mg/kg in rats.
        - label: Reproductive signal
          line: PubChem's aggregate includes H360 at 22.6% and H362 at 43.8% of company reports, while the SDS says reproductive or developmental effects are not expected.
    - title: If it fails
      lead: The failure routes found in the sources are supply and fire.
      points:
        - label: Supply
          line: China produced 80% of refined tellurium in 2025. European prices rose 84% to an estimated $150 per kg, according to the USGS, after export controls.
        - label: Fire
          line: The powder is a flammable solid, and a fire gives off gases hazardous to health.
  recipe:
    line: Tellurium is the element Te (PubChem). Wikipedia says tellurium-bearing compounds were first found in the 18th century, and that Martin Heinrich Klaproth named the element. The USGS says more than 90% is produced from the anode slimes of copper electrolytic refining, and the rest from lead-refining skimmings and from flue dusts and gases.
    parts:
      - name: Tellurium
        symbol: Te
        atoms: 1
        atomic_weight: 127.6
        share_percent: 100
        role: The element. Sold as high-purity tellurium, as tellurium dioxide, or inside CdTe and bismuth telluride compounds.
  why: Tellurium is a brittle metalloid whose value comes from the compounds it forms. Cadmium telluride makes thin-film solar panels and bismuth telluride makes thermoelectric coolers and generators. The USGS puts these at 70% and 15% of 2025 global end use. It is also a small machinability additive in steel and copper alloys.
  uses:
    - where: Solar panels
      line: Cadmium telluride thin-film solar cells take most of the element. The USGS estimates 70% of 2025 global tellurium end use. Lamb et al. (2017) tested CdTe cells on cerium-doped space cover glass in a laboratory proton-irradiation test.
    - where: Thermoelectric devices
      line: Witting et al. (2019) describe bismuth telluride as the working material for most Peltier cooling devices and thermoelectric generators. The USGS estimates 15% of 2025 end use.
    - where: Steel and copper alloys
      line: Tellurium improves machinability in steel and, as a minor additive, in copper alloys without reducing conductivity (USGS).
  can_do:
    - label: Melt
      value: 449.5 °C
      benchmark: melting_point
      line: Melts at 449.5 °C (PubChem).
    - label: Carry heat
      value: 3 W/(m·K)
      benchmark: thermal_conductivity
      line: Thermal conductivity is 3 W/(m·K) per WebElements, with no temperature stated.
    - label: Stiffness
      value: 43 GPa
      benchmark: elastic_modulus
      line: Young's modulus is 43 GPa (WebElements).
    - label: Density
      value: 6.0 to 6.25 g/cm3
      benchmark: density
      line: PubChem gives a density range of 6.0 to 6.25 g/cm3.
  compare: Tellurium is not used as a structural metal. It melts at 449.5 °C and boils at 988 °C, and its stiffness (Young's modulus 43 GPa) and hardness describe a brittle solid. Its main value lies in the compounds it forms with cadmium and bismuth. The sources read here give no direct comparison with other elements, so none is made.
  compare_rows:
    - scope: material
      label: Density
      benchmark: density
    - scope: material
      label: Melting point
      benchmark: melting_point
    - scope: material
      label: Thermal conductivity
      benchmark: thermal_conductivity
  good_for:
    - 'CdTe thin-film solar cells, the largest use (USGS: 70% of 2025 end use).'
    - Bismuth telluride thermoelectric coolers and generators (Witting et al. 2019).
  watch_out:
    - 'Toxicity: toxic if swallowed (Materion), with conflicting reproductive-toxicity classifications (PubChem).'
    - 'Supply: China produced 80% of refined output in 2025, and export controls raised European prices.'
    - 'Copper dependence: most tellurium is recovered from copper refining residues (USGS).'
  handling:
    - Keep dust down and use local exhaust where it forms, with the 0.1 mg/m3 limit from the SDS in view.
    - Keep away from heat, sparks and open flame, and away from strong oxidizing agents and chlorine.
    - Check the supplier SDS for the form handled, because the hazard data disagree.
  verdict: 'Tellurium is a by-product metal whose main uses are solar cells and thermoelectric devices. Its physical properties are documented from several sources. The space record is thin: the only space-related source found is a laboratory proton test of CdTe cells, not an orbital result for elemental tellurium. Its hazards need the supplier SDS, and its supply depends on China and on copper refining.'