Germanium Ge

spore: profile
id: germanium
spore_version: 0.2
family: semiconductor-materials
name: Germanium
abbreviation: Ge
role: semiconductor
category: semiconductors
type: silicon
summary: Germanium is the element Ge, a semiconductor with a band gap of 0.66 eV at 300 K (EE Semi). Crystran gives its transmission as 1.8 to 23 µm and its refractive index as 4.0026 at 11 µm, which makes it a standard lens and window material for infrared and thermal imaging. Triple-junction space solar cells from Spectrolab and Emcore are built on germanium substrates. The USGS says the United States imports more than half of the germanium it consumes, and that China banned germanium exports to the United States in December 2024.
best_for: Infrared optics from 1.8 to 23 µm (thermal-imaging lenses, ATR prisms) and substrates for triple-junction space solar cells
weakest_at: 'Temperature limit and supply: Crystran says germanium becomes opaque at all wavelengths a little above 350 K, and the USGS says supply runs through a few producers, China the leading one'
identity:
  formula: Ge, elemental germanium, diamond-cubic crystal structure (Fd3m)
  source: crystran-ge
  where: Product Data table, Class/Structure row (Cubic Diamond, Fd3m) and Molecular Weight row (72.59); EE Semi table, Crystal Structure row (Diamond)
tags:
  environments: []
  stresses: []
  applications:
    - optics-and-cameras
    - electronics-and-chips
    - solar-arrays
properties:
  - benchmark: density
    label: Density
    value: 5.3267
    unit: g/cm3
    scope: material
    conditions:
      temperature: 300 K (table title)
    method: Value printed in a materials property table
    status: ground
    source: eesemi
    where: Table Properties of Si, Ge and GaAs at 300 K, row Density (g/cm 3), Ge column
  - benchmark: density
    label: Density (optics data)
    value: 5.33
    unit: g/cc
    scope: material
    conditions:
      temperature: not stated on the page
    method: Value printed on a manufacturer product data page
    status: ground
    source: crystran-ge
    where: Product Data table, Density row
  - benchmark: melting_point
    label: Melting point (semiconductor table)
    value: 937
    unit: °C
    scope: material
    conditions:
      basis: melting point as printed, no pressure or purity stated
    method: Value printed in a materials property table
    status: ground
    source: eesemi
    where: Table Properties of Si, Ge and GaAs at 300 K, row Melting Point (deg C), Ge column
  - benchmark: melting_point
    label: Melting point (optics data)
    value: 936
    unit: °C
    scope: material
    conditions:
      basis: melting point as printed, no pressure or purity stated
    method: Value printed on a manufacturer product data page
    status: ground
    source: crystran-ge
    where: Product Data table, Melting Point row (footnote 3)
  - benchmark: bandgap
    label: Energy band gap at 300 K
    value: 0.66
    unit: eV
    scope: material
    conditions:
      temperature: 300 K (table title)
    method: Value printed in a materials property table
    status: ground
    source: eesemi
    where: Table at 300 K, row Energy Gap at 300K (eV), Ge column
  - benchmark: dielectric_constant
    label: Dielectric constant at 300 K
    value: 16
    unit: '-'
    scope: material
    conditions:
      temperature: 300 K (table title)
    method: Value printed in a materials property table (no unit printed)
    status: ground
    source: eesemi
    where: Table at 300 K, row Dielectric Constant, Ge column
  - benchmark: dielectric_constant
    label: Dielectric constant at microwave frequency
    value: 16.6
    unit: '-'
    scope: material
    conditions:
      frequency: 9.37 GHz
      temperature: 300 K
    method: Value printed on a manufacturer product data page
    status: ground
    source: crystran-ge
    where: Product Data table, Dielectric Constant row
  - benchmark: electron_mobility
    label: Electron drift mobility
    value: 3900
    unit: cm2/(V·s)
    scope: material
    conditions:
      temperature: 300 K (table title)
      type: drift mobility, doping not stated
    method: Value printed in a materials property table
    status: ground
    source: eesemi
    where: Table at 300 K, row Mobility (Drift) electrons, Ge column
  - benchmark: hole_mobility
    label: Hole drift mobility
    value: 1900
    unit: cm2/(V·s)
    scope: material
    conditions:
      temperature: 300 K (table title)
      type: drift mobility, doping not stated
    method: Value printed in a materials property table
    status: ground
    source: eesemi
    where: Table at 300 K, row Mobility (Drift) holes, Ge column
  - benchmark: intrinsic_resistivity
    label: Intrinsic resistivity
    value: 47
    unit: Ω·cm
    scope: material
    conditions:
      temperature: 300 K (table title)
      doping: intrinsic, undoped
    method: Value printed in a materials property table
    status: ground
    source: eesemi
    where: Table at 300 K, row Intrinsic Resistivity (ohm-cm), Ge column
  - benchmark: electron_affinity
    label: Electron affinity
    value: 4
    unit: V
    scope: material
    conditions:
      temperature: 300 K (table title)
    method: Value printed in a materials property table
    status: ground
    source: eesemi
    where: Table at 300 K, row Electron Affinity (V), Ge column
  - benchmark: lattice_constant
    label: Lattice constant
    value: 5.64613
    unit: Å
    scope: material
    conditions:
      temperature: 300 K (table title)
    method: Value printed in a materials property table, in angstroms as printed
    status: ground
    source: eesemi
    where: Table at 300 K, row Lattice Constant (angstroms), Ge column
  - benchmark: thermal_conductivity
    label: Thermal conductivity
    value: 58.62
    unit: W/(m·K)
    scope: material
    conditions:
      temperature: 293 K
    method: Value printed on a manufacturer product data page
    status: ground
    source: crystran-ge
    where: Product Data table, Thermal Conductivity row (printed as 58.62 W m-1 K-1 @ 293 K)
  - benchmark: cte
    label: Linear thermal expansion (table at 300 K)
    value: 5.8
    unit: ppm/K
    scope: material
    conditions:
      temperature: 300 K (table title)
      unit_in_source: 5.8 x 10 -6 per deg C
    method: Value printed as 5.8 x 10 -6 (1/deg C) in a materials property table; the number is the same in ppm/K, so no scaling is needed
    status: ground
    source: eesemi
    where: Table at 300 K, row Linear Coefficient of Thermal Expansion, Ge column
  - benchmark: cte
    label: Linear thermal expansion (optics data)
    value: 6.1
    unit: ppm/K
    scope: material
    conditions:
      temperature: 298 K
      unit_in_source: 6.1 x 10-6/°C
    method: Value printed as 6.1 x 10-6/°C on a manufacturer product data page; the number is the same in ppm/K, so no scaling is needed
    status: ground
    source: crystran-ge
    where: Product Data table, Thermal Expansion row (footnotes 3, 4, 6)
  - benchmark: specific_heat
    label: Specific heat capacity
    value: 310
    unit: J/(kg·K)
    scope: material
    conditions:
      temperature: not stated on the page
    method: Value printed on a manufacturer product data page
    status: ground
    source: crystran-ge
    where: Product Data table, Specific Heat Capacity row (printed as 310 J Kg-1 K-1)
  - benchmark: elastic_modulus
    label: Young's modulus
    value: 102.7
    unit: GPa
    scope: material
    conditions:
      temperature: not stated on the page
    method: Value printed on a manufacturer product data page
    status: ground
    source: crystran-ge
    where: Product Data table, Youngs Modulus (E) row
  - benchmark: shear_modulus
    label: Shear modulus
    value: 67
    unit: GPa
    scope: material
    conditions:
      temperature: not stated on the page
    method: Value printed on a manufacturer product data page
    status: ground
    source: crystran-ge
    where: Product Data table, Shear Modulus (G) row
  - benchmark: bulk_modulus
    label: Bulk modulus
    value: 77.2
    unit: GPa
    scope: material
    conditions:
      temperature: not stated on the page
    method: Value printed on a manufacturer product data page
    status: ground
    source: crystran-ge
    where: Product Data table, Bulk Modulus (K) row
  - benchmark: poissons_ratio
    label: Poisson's ratio
    value: 0.28
    unit: '-'
    scope: material
    conditions:
      temperature: not stated on the page
    method: Value printed on a manufacturer product data page
    status: ground
    source: crystran-ge
    where: Product Data table, Poisson Ratio row
  - benchmark: refractive_index
    label: Refractive index in the thermal infrared
    value: 4.0026
    unit: '-'
    scope: material
    conditions:
      wavelength: 11 µm
      temperature: not stated on the page
    method: Value printed on a manufacturer product data page (references Palik and Li 1980)
    status: ground
    source: crystran-ge
    where: Product Data table, Refractive Index row (printed as 4.0026 at 11 μm)
  - benchmark: transmission_range
    label: Transmission range
    value: 1.8
    value_high: 23
    unit: µm
    scope: material
    conditions:
      basis: range as printed on the product data page (footnote 1, Palik handbook)
    method: Value printed on a manufacturer product data page
    status: ground
    source: crystran-ge
    where: Product Data table, Transmission Range row (printed as 1.8 to 23 μm)
corrosion:
  - environment: Ambient air at room temperature
    headline: A very thin layer of germanium dioxide protects the surface of germanium.
    effect: WebElements says the surface of lumps of germanium is protected by a very thin layer of germanium dioxide, GeO2, and that germanium is more reactive than silicon, but not by much. No thickness is given.
    rating: low
    conditions:
      basis: Rating is the assistant's reading of a protective oxide, not a printed rating
    source: webelements-ge
    where: Chemistry page, Reaction of germanium with water paragraph (first sentences)
  - environment: Water
    headline: The oxide layer makes germanium more or less inert to water.
    effect: WebElements says the oxide layer renders germanium more or less inert to water. Crystran lists germanium as insoluble in water (Solubility row), but no solubility number was read.
    rating: low
    conditions:
      basis: Rating is the assistant's reading of the wording, not a printed rating
    source: webelements-ge
    where: Chemistry page, Reaction of germanium with water paragraph
  - environment: Oxygen at red heat
    headline: At red heat germanium reacts with oxygen in air to form germanium dioxide.
    effect: WebElements says that at red heat, germanium reacts with oxygen in air to form germanium dioxide. Temperature and rate are not given.
    rating: moderate
    conditions:
      basis: Rating is the assistant's reading; no rate or temperature number was read
    source: webelements-ge
    where: Chemistry page, Reaction of germanium with oxygen paragraph
risks:
  hazards:
    - text: PubChem's entry for germanium (EC 231-164-3, ECHA notifications) gives 186 of 319 company reports as not meeting GHS hazard criteria. The other reports give H228 (13.5%), H361 (27.3%), H373 (27.3%) and H412 (27%).
      ghs:
        - 'H228: Flammable solid'
        - 'H361: Suspected of damaging fertility or the unborn child'
        - 'H373: May causes damage to organs through prolonged or repeated exposure'
        - 'H412: Harmful to aquatic life with long lasting effects'
      source: pubchem-ge
      where: Safety and Hazards, GHS Classification (CID 6326954), ECHA C&L Notifications Summary
    - text: PubChem lists the signal word Danger, pictograms GHS02 (flammable) and GHS08 (health hazard), and precautionary codes P203, P210, P240, P241, P260, P273, P280, P318, P319, P370+P378, P405 and P501. The statement text for these codes was not checked, so use the supplier SDS for the form handled.
      ghs: []
      source: pubchem-ge
      where: Safety and Hazards, GHS Classification, Signal and Precautionary Statement Codes
  failure_risks:
    - mode: Loss of transmission at high temperature
      trigger: Operation a little above 350 K
      consequence: Crystran says germanium becomes opaque at all wavelengths a little above 350 K, as the band gap floods with thermal electrons. Its refractive index also changes rapidly with temperature.
      severity: high
      source: crystran-ge
      where: Description paragraph, final sentence
    - mode: Supply interruption
      trigger: China's export licensing (August 2023) and its ban on exports to the United States (December 2024)
      consequence: USGS reports that US imports of germanium metal fell by 67% in 2025 to an estimated 7,000 kg, and that US net import reliance was above 50% in every year from 2021 to 2025e.
      severity: high
      source: usgs-ge-2026
      where: Events, Trends, and Issues; Salient Statistics, Net import reliance row
  side_effects: []
  handling:
    - text: Keep germanium optics below about 350 K. Above that the material becomes opaque at all wavelengths (Crystran).
      source: crystran-ge
      where: Description paragraph, final sentence
    - text: PubChem's GHS entry is an aggregate of company reports, so check the supplier SDS for the form handled (powder, wafer or lens).
      source: pubchem-ge
      where: Safety and Hazards, GHS Classification
  mitigations: []
uses:
  - application: optics-and-cameras
    device: Infrared lenses and windows for thermal imaging
    example: Crystran says germanium covers the 8 to 14 micron thermal band and is used in lens systems for thermal imaging.
    source: crystran-ge
    where: Description paragraph
  - application: optics-and-cameras
    device: ATR prisms for infrared spectroscopy
    example: Crystran says germanium is used to manufacture attenuated total reflection (ATR) prisms for spectroscopy, and that its refractive index makes it an effective natural 50% beamsplitter without coatings.
    source: crystran-ge
    where: Description paragraph
  - application: optics-and-cameras
    device: Optical fibre glass
    example: The USGS says germanium dioxide and tetrachloride are consumed to make fibre optic glass for data networking and telecommunication.
    source: usgs-ge-2026
    where: Events, Trends, and Issues
  - application: electronics-and-chips
    device: High-purity germanium radiation detectors
    example: The USGS lists high-purity germanium radiation detectors among the end uses of germanium metal.
    source: usgs-ge-2026
    where: Events, Trends, and Issues
  - application: solar-arrays
    device: Germanium substrate for triple-junction space solar cells
    example: Spectrolab's GaInP2/GaAs/Ge cell has a germanium substrate and a minimum average beginning-of-life efficiency of 26.8% at 28 °C, AM0.
    source: spectrolab-tnj
    where: 'First page, Features and Product Description (Substrate: Germanium); Typical Electrical Parameters'
  - application: solar-arrays
    device: Lattice-matched GaInP2/InGaAs/Ge triple-junction cell
    example: Emcore reports that its lattice-matched GaInP2/InGaAs/Ge triple-junction device has achieved the highest power conversion efficiency and the most commercial success for space applications. Its histogram of over 100,000 large-area devices has an average efficiency of 27.6%.
    source: emcore-ntrs-2009
    where: Introduction; Current Technology, first paragraph
supply:
  - subject: Germanium metal and germanium dioxide (fibre optics, infrared optics, semiconductors, solar-cell substrates and radiation detectors)
    abundance: The USGS summary gives no abundance figure. It says resources are associated with certain zinc and lead-zinc-copper sulfide ores and lignite coal deposits, and that reserves data were not widely reported at a mine or country level.
    producers: []
    us_position: 'US imports of germanium metal were 22,000 kg in 2023, 21,000 kg in 2024 and an estimated 7,000 kg in 2025e. Import sources 2021 to 2024: germanium metal from China 41%, Belgium 27%, Germany 25%; germanium dioxide from Belgium 57%, Canada 37%. China was the leading global producer, and in 2025 its exports of germanium metal went mostly to Russia (28%), Belgium (26%), Germany (26%) and Japan (18%).'
    price: 'Average European price for 99.999% purity: $4,100 per kg for metal and $2,500 per kg for dioxide in 2025e (Argus, via USGS)'
    critical_lists:
      - list: USGS 2025 List of Critical Minerals (listed in the IEA summary; germanium listed for fibre optics, semiconductors and night vision systems)
        listed: true
    recycling: The USGS says much germanium removed in machining infrared optics is routinely recycled as new scrap, infrared lenses and windows from decommissioned military equipment are recycled, and germanium wafers used as solar-cell substrates are recycled.
    substitutes:
      - 'USGS: silicon or gallium arsenide substitute for germanium in certain electronic applications, and chalcogenide glass has been used in infrared applications.'
    source: usgs-ge-2026
    where: Import Sources (2021 to 2024); Salient Statistics; Events, Trends, and Issues; Recycling; Substitutes
media: []
documents:
  - title: USGS Mineral Commodity Summaries 2026, Germanium
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-germanium.pdf
  - title: PubChem record for germanium (CID 6326954), GHS classification and molecular weight
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/compound/6326954
  - title: Crystran, Germanium Ge optical material data sheet and product data
    type: datasheet
    url: https://www.crystran.co.uk/optical-materials/germanium-ge
  - title: Spectrolab, Improved Triple Junction (ITJ) solar cell data sheet
    type: datasheet
    url: https://www.spectrolab.com/DataSheets/TNJCell/tnj.pdf
gaps:
  - 'Band gap type (direct or indirect): not stated in the sources read.'
  - 'Acid and alkali corrosion (for example in HCl, HNO3 or KOH): WebElements has these sections, but their text was not in the page that was fetched.'
  - 'Solubility of germanium dioxide: the Feldmann et al. 2018 chapter (Springer) could not be read (the page returned only an abstract stub), and the ECS and SEMATECH abstracts were seen only as search snippets, so no number was taken from them.'
  - Knoop hardness 780 is printed on the Crystran page with no unit, so it is not given as a value.
  - 'Intrinsic carrier concentration 2.4 x 10 13 cm-3 (EE Semi) and the dn/dT value +396 x 10-6 K-1 (Crystran) are left out: both are printed in exponent form that the value check cannot match. Breakdown-field and effective-density-of-states values from EE Semi are left out for the same reason.'
  - 'Ge world production shares: the USGS summary read gives no world production table for germanium, only US import shares for 2021 to 2024 and the statement that China is the leading producer.'
  - 'Occupational exposure limit (OSHA PEL, NIOSH REL or ACGIH TLV) for germanium: not found in this run.'
  - 'Radiation damage to germanium itself: not found. The Spectrolab datasheet gives electron-fluence degradation for the finished cell, not for the bare substrate.'
  - 'Crystal growth details (Czochralski conditions, dopants, resistivity grades): Crystran names the method and the countries of manufacture only, so no process conditions are given.'
  - 'Critical-mineral lists (EU): not checked in this run.'
  - 'Property names not in spores/property-canon.yaml and used here: bandgap, electron_mobility, hole_mobility, intrinsic_resistivity, electron_affinity, lattice_constant, transmission_range. Dielectric_constant and refractive_index are canonical.'
  - Hazard statement texts for the PubChem precautionary codes (P203 to P501) were not checked; only the codes are listed. The ECHA hazard percentages are from PubChem's aggregate of company reports.
sources:
  eesemi:
    title: EE Semi, Properties of Silicon (Si), Germanium (Ge), and Gallium Arsenide (GaAs) at 300 deg K
    url: https://www.eesemi.com/sigegaas.htm
    kind: web
    license: page content, cited as published
  crystran-ge:
    title: Crystran, Germanium Ge optical material page (product data, refractive index and references)
    url: https://www.crystran.co.uk/optical-materials/germanium-ge
    kind: datasheet
    license: page content, cited as published
  usgs-ge-2026:
    title: USGS Mineral Commodity Summaries 2026, Germanium (February 2026)
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-germanium.pdf
    kind: report
    license: public domain (USGS), cited as published
  pubchem-ge:
    title: PubChem, Germanium (CID 6326954), GHS classification and molecular weight
    url: https://pubchem.ncbi.nlm.nih.gov/compound/6326954
    kind: database
    license: public domain (NCBI), cited as published
  webelements-ge:
    title: 'WebElements, Germanium: chemistry (reactions with oxygen and water)'
    url: https://webelements.co.uk/germanium/chemistry.html
    kind: web
    license: page content, cited as published
  emcore-ntrs-2009:
    title: Sharps et al., Space Solar Cell Research and Development Projects at Emcore Photovoltaics (NASA NTRS 20090022287)
    url: https://ntrs.nasa.gov/citations/20090022287
    kind: paper
    license: public domain (NASA), cited as published
  spectrolab-tnj:
    title: Spectrolab, Improved Triple Junction (ITJ) Solar Cells data sheet
    url: https://www.spectrolab.com/DataSheets/TNJCell/tnj.pdf
    kind: datasheet
    license: page content, cited as published
  iea-crit-2025:
    title: IEA, Final List of Critical Minerals 2025 (summary of the USGS list, November 2025)
    url: https://www.iea.org/policies/31799
    kind: web
    license: page content, cited as published
license: CC-BY-4.0
checked_values: 22
updated: '2026-10-26'
story:
  risk_groups:
    - title: For people
      lead: PubChem's aggregate for germanium mixes 186 'not classified' reports with notifications that carry H361 and H373, each at 27.3%. Check the supplier SDS before handling.
      level: 1
      verdict: Some reports flag reproductive and organ toxicity; the SDS…
      points:
        - label: Aggregate hazard codes
          line: PubChem's ECHA-based aggregate lists H228 (13.5%), H361 (27.3%), H373 (27.3%) and H412 (27%) across 319 company reports. No exposure limit was found, so none is given.
    - title: If it fails
      lead: Failure routes found in the sources are about temperature and supply.
      points:
        - label: Heat
          line: Crystran says germanium becomes opaque at all wavelengths a little above 350 K, so warm optics lose their use.
        - label: Supply
          line: The USGS reports that US imports of germanium metal fell 67% in 2025, after China's ban on exports to the United States.
  recipe:
    line: Germanium is the element Ge (PubChem). Crystran says a small number of manufacturers in Belgium, the USA, China and Russia grow germanium by the Czochralski technique. The USGS says germanium is recovered from zinc concentrates, through a refinery that produces the dioxide and tetrachloride, and that its resources are associated with zinc and lead-zinc-copper sulfide ores and lignite coal deposits.
    parts:
      - name: Germanium
        symbol: Ge
        share_percent: 100
        role: Element. Grown as a single crystal for optics and wafers, and supplied as germanium metal and germanium dioxide for other uses.
        source: pubchem-ge
        where: Compound record, Molecular Weight (CID 6326954)
  why: Germanium combines a high refractive index with transmission from 1.8 to 23 µm and a 0.66 eV band gap, which suits infrared optics and space-cell substrates. The USGS says the United States relies on imports for more than half of the germanium it consumes.
  uses:
    - where: Infrared optics
      line: Lenses and windows for thermal imaging across the 8 to 14 micron band, and ATR prisms for spectroscopy (Crystran).
    - where: Fibre optics and space solar cells
      line: The USGS lists fibre optics first among US end uses of germanium, ahead of infrared optics and semiconductors. Triple-junction space solar cells from Spectrolab and Emcore use germanium substrates.
  can_do:
    - label: Pass infrared light
      value: 1.8 to 23 µm
      benchmark: transmission_range
      line: Crystran gives the transmission range as 1.8 to 23 µm.
    - label: Bend light
      value: '4.0026'
      benchmark: refractive_index
      line: The refractive index is 4.0026 at 11 µm, high enough for a natural 50% beamsplitter without coatings (Crystran).
    - label: Act as a semiconductor
      value: 0.66 eV
      benchmark: bandgap
      line: The band gap at 300 K is 0.66 eV (EE Semi), narrower than silicon's in the same table.
    - label: Carry heat
      value: 58.62 W/(m·K)
      benchmark: thermal_conductivity
      line: Thermal conductivity is 58.62 W/(m·K) at 293 K (Crystran).
  compare: Against silicon in the same EE Semi table at 300 K, germanium has a narrower band gap, a higher electron drift mobility, and a density more than twice silicon's. Its melting point is also lower than silicon's in that table. Germanium also becomes opaque at all wavelengths a little above 350 K (Crystran), a limit that the sources read here do not give for silicon.
  good_for:
    - 'Thermal imaging optics: a lens or window material across the 8 to 14 micron thermal band.'
    - 'Triple-junction space solar cells: germanium is the substrate under the GaInP2/GaAs/Ge stack, with a 26.8% minimum average beginning-of-life efficiency for the Spectrolab cell.'
  watch_out:
    - 'Temperature: germanium becomes opaque at all wavelengths a little above 350 K.'
    - 'Supply: the USGS puts China as the leading producer, with exports to the United States banned since December 2024.'
    - Thermal conductivity is far below the metals, so germanium does not spread heat well.
  verdict: Germanium is well documented for infrared optics and space-cell substrates. Its density, melting point, band gap and dielectric constant are printed in more than one source, and its infrared transmission range and refractive index come from a product data page that cites the handbook. Its weak points are the 350 K opacity limit and a supply chain the USGS describes as concentrated in China. Acid and alkali corrosion, solubility numbers and an occupational exposure limit were not found in this run.
  handling:
    - Keep germanium optics below about 350 K. Above that the material becomes opaque at all wavelengths (Crystran).
    - Check the supplier SDS for the form handled, because the PubChem GHS entry is an aggregate of company reports with mixed hazard codes.
  compare_rows:
    - scope: material
      label: Density
      benchmark: density
    - scope: material
      label: Melting point
      benchmark: melting_point
    - scope: material
      label: Thermal conductivity
      benchmark: thermal_conductivity