spore: profile
id: lithium-fluoride
spore_version: 0.2
family: optical-crystals
name: Lithium fluoride (single-crystal LiF)
abbreviation: LiF
role: VUV and X-ray optical crystal, with dosimetry and battery-interphase uses
category: glasses-optics
type: optical-crystals
summary: |
  Lithium fluoride is the cubic NaCl-structure crystal LiF. Crystran grows it by the vacuum Stockbarger method in ingots about 100 mm in diameter and says it has the most extreme UV transmission of all its materials, reaching the hydrogen Lyman-alpha line at 121 nm. Its data sheet gives a refractive index of 1.392 at 0.6 µm, a transmission range of 0.12 to 6 µm, a density of 2.639 g/cc and a melting point of 848 °C, and it says the crystal cleaves easily. Lithium fluoride is also used in thermoluminescent dosimeters, and a 2020 PNAS study finds that its role in lithium-metal battery interphases is limited by its mechanical integrity. The sources read give no space or radiation-ageing test for lithium fluoride.
best_for: Optics that must transmit into the vacuum ultraviolet, down to 121 nm (Crystran)
weakest_at: 'Brittleness: the crystal cleaves easily on (100), and it reacts with strong mineral acids (Crystran; SDS)'
identity:
  formula: LiF
  cas: 7789-24-4
  crystal_system: cubic
  space_group: Fm3m (#221), NaCl structure
  source: crystran-lif-datasheet
  where: Class/Structure row (Cubic FCC, Fm3m (#221), NaCl structure, (100) cleavage); CAS 7789-24-4 and EC 232-152-0 from crystran-lif-msds section 3.1; molecular weight 25.94 on the Crystran data sheet
tags:
  environments: []
  stresses: []
  applications:
    - optics-and-cameras
    - batteries
    - habitats-and-suits
properties:
  - benchmark: refractive_index
    label: Refractive index at 0.6 µm
    value: 1.392
    unit: '-'
    scope: material
    conditions:
      wavelength: 0.6 µm
    method: Value printed on the Crystran materials data sheet (footnote 1, Laporte et al., J. Opt. Soc. Am. 73, 1062); the same sheet prints a reflection loss of 5.2 percent at 0.6 µm
    status: ground
    source: crystran-lif-datasheet
    where: Data table, Refractive Index row (1.392 at 0.6µm)
  - benchmark: refractive_index
    label: Refractive index at 5 µm
    value: 1.3266
    unit: '-'
    scope: material
    conditions:
      wavelength: 5 µm
    method: Value printed in the refractive index table of the Crystran data sheet
    status: ground
    source: crystran-lif-datasheet
    where: Refractive Index table, row 5.000 µm
  - benchmark: transmission_range
    label: Transmission range
    value: 0.12
    value_high: 6
    bound: range
    unit: µm
    scope: material
    conditions:
      thickness: not stated on the page
    method: Range printed on the Crystran data sheet; the Crystran product page gives the same range
    status: ground
    note: The data sheet shows a VUV transmission curve for a 1 mm to 48 mm sample range; the range is taken from the data table, not the curve.
    source: crystran-lif-datasheet
    where: Data table, Transmission Range row
  - benchmark: density
    label: Density
    value: 2.639
    unit: g/cc
    scope: material
    conditions:
      temperature: not stated on the page
    method: Value printed on a manufacturer materials data sheet
    status: ground
    source: crystran-lif-datasheet
    where: Data table, Density row
  - benchmark: melting_point
    label: Melting point
    value: 848
    unit: °C
    scope: material
    conditions:
      form: single crystal
    method: Value printed on the Crystran data sheet (footnote 6, Douglas and Dever, J. Am. Chem. Soc. 1954)
    status: ground
    note: The Crystran safety data sheet prints 842 C for the same material; the data sheet value is used.
    source: crystran-lif-datasheet
    where: Data table, Melting Point row
  - benchmark: boiling_point
    label: Boiling point
    value: 1676
    unit: °C
    scope: material
    conditions:
      pressure: 760 mmHg
    method: Value printed in section 9.1 of the Crystran safety data sheet
    status: ground
    source: crystran-lif-msds
    where: Section 9.1, BOILING POINT (760mm Hg) row
  - benchmark: thermal_conductivity
    label: Thermal conductivity
    value: 11.3
    unit: W/(m·K)
    scope: material
    conditions:
      temperature: 314 K
    method: Value printed on the Crystran data sheet (footnote 2, Combes et al. 1951)
    status: ground
    source: crystran-lif-datasheet
    where: Data table, Thermal Conductivity row
  - benchmark: cte
    label: Coefficient of thermal expansion
    value: 37
    unit: ppm/K
    scope: material
    conditions:
      unit_in_source: x 10-6 K-1
      temperature: 283 K
    method: Printed as 37 x 10-6 K-1 on the data sheet, which is the same as ppm/K; no conversion of the number
    status: ground
    source: crystran-lif-datasheet
    where: Data table, Thermal Expansion row
  - benchmark: specific_heat
    label: Specific heat capacity
    value: 1562
    unit: J/(kg·K)
    scope: material
    conditions:
      temperature: not stated on the page
    method: Value printed on a manufacturer materials data sheet
    status: ground
    source: crystran-lif-datasheet
    where: Data table, Specific Heat Capacity row
  - benchmark: elastic_modulus
    label: Young's modulus
    value: 64.97
    unit: GPa
    scope: material
    conditions:
      temperature: not stated on the page
    method: Value printed on the Crystran data sheet (footnote 2, Combes et al. 1951)
    status: ground
    source: crystran-lif-datasheet
    where: Data table, Youngs Modulus (E) row
  - benchmark: shear_modulus
    label: Shear modulus
    value: 55.14
    unit: GPa
    scope: material
    conditions:
      temperature: not stated on the page
    method: Value printed in the PDF data sheet
    status: ground
    note: The Crystran product web page prints 54.14 GPa for the same material; the PDF value is used.
    source: crystran-lif-datasheet
    where: Data table, Shear Modulus (G) row
  - benchmark: bulk_modulus
    label: Bulk modulus
    value: 62.03
    unit: GPa
    scope: material
    conditions:
      temperature: not stated on the page
    method: Value printed on a manufacturer materials data sheet
    status: ground
    source: crystran-lif-datasheet
    where: Data table, Bulk Modulus (K) row
  - benchmark: poissons_ratio
    label: Poisson ratio
    value: 0.326
    unit: '-'
    scope: material
    conditions:
      temperature: not stated on the page
    method: Printed on the data sheet as calculated by the supplier
    status: ground
    source: crystran-lif-datasheet
    where: Data table, Poisson Ratio row
  - benchmark: apparent_elastic_limit
    label: Apparent elastic limit
    value: 11.2
    unit: MPa
    scope: material
    conditions:
      temperature: not stated on the page
    method: Value printed on the data sheet as 11.2 MPa (1620 psi); not a canonical property name
    status: ground
    source: crystran-lif-datasheet
    where: Data table, Apparent Elastic Limit row
  - benchmark: reststrahlen_peak
    label: Reststrahlen peak
    value: 25
    unit: µm
    scope: material
    conditions:
      temperature: not stated on the page
    method: Value printed on the data sheet; not a canonical property name
    status: ground
    source: crystran-lif-datasheet
    where: Data table, Reststrahlen Peak row
  - benchmark: refractive_index_temperature_coefficient
    label: Refractive index change with temperature (dn/dT)
    value: -16
    unit: ppm/K
    scope: material
    conditions:
      unit_in_source: x 10-6 K-1
      wavelength: 1.15 µm
    method: Printed as -16 x 10-6 at 1.15 µm on the data sheet, which is the same as ppm/K; not a canonical property name
    status: ground
    source: crystran-lif-datasheet
    where: Data table, dn/dT row
  - benchmark: water_solubility
    label: Solubility in water at 20 °C
    value: 0.27
    unit: g/100 g water
    scope: material
    conditions:
      temperature: 20 °C
    method: Value printed on the data sheet; the safety sheet prints the same figure as 270 mg/100 ml at 20 C; not a canonical property name
    status: ground
    source: crystran-lif-datasheet
    where: Data table, Solubility row
corrosion:
  - environment: Strong mineral acids and strong oxidising materials
    headline: Lithium fluoride reacts with strong mineral acids and strong oxidising materials, and gives off hydrogen fluoride gas in contact with a mineral acid.
    effect: The Crystran safety sheet lists strong mineral acids and strong oxidising materials as incompatible, says it avoids acids, particularly hot concentrated sulphuric acid, and gives hydrogen fluoride as the decomposition product. No rate or concentration is printed, so the rating is qualitative.
    rating: moderate
    conditions:
      basis: qualitative reactivity statement; no rate or concentration printed
      agent: strong mineral acids and strong oxidising materials
    source: crystran-lif-msds
    where: Sections 7.2, 10.1, 10.4, 10.5 and 10.6
  - environment: Water at 20 °C
    headline: Lithium fluoride is slightly soluble in water.
    effect: The data sheet gives a solubility of 0.27 g per 100 g of water at 20 C, and the safety sheet says slightly soluble, 270 mg per 100 ml at 20 C. The safety sheet also lists the material as hazardous to drinking water. No dissolution or corrosion test is printed.
    rating: low
    conditions:
      temperature: 20 °C
      note: solubility figure, not a corrosion rate
    source: crystran-lif-datasheet
    where: Data table, Solubility row; crystran-lif-msds sections 9.1 and 12.1
risks:
  hazards:
    - text: The Crystran safety sheet (revision 2026) classes lithium fluoride as a Class 6.1 poison, with signal word Warning and the statements H302 (harmful if swallowed), H315 (causes skin irritation), H319 (causes serious eye irritation) and H332 (harmful if inhaled).
      ghs:
        - H302
        - H315
        - H319
        - H332
      source: crystran-lif-msds
      where: Sections 2.1 and 2.2
    - text: The same sheet gives an oral LD50 above 143 mg/kg in rats and 119 mg/kg in mice, and says that if swallowed the material causes nausea, vomiting, stomach pains and diarrhoea.
      ghs: []
      source: crystran-lif-msds
      where: Sections 2.1 and 11.1
    - text: The sheet gives an occupational exposure limit of 2.5 mg/m3 as fluoride, as an 8 hour time-weighted average, and advises avoiding dust.
      ghs: []
      source: crystran-lif-msds
      where: Sections 6.1 and 8.1
    - text: For transport the sheet gives UN 3288, Toxic solid, inorganic, N.O.S. (Lithium Fluoride), class 6.1, packing group III, and marine pollutant.
      ghs: []
      source: crystran-lif-msds
      where: Section 14
  failure_risks:
    - mode: Cleavage on (100)
      trigger: Impact, mechanical stress, or polishing at steep radii
      consequence: The data sheet says lithium fluoride cleaves easily and must be worked with extreme care, and that polishing, particularly at steep radii, often causes surface rip-out. The apparent elastic limit is 11.2 MPa.
      severity: moderate
      source: crystran-lif-datasheet
      where: Introduction text; Apparent Elastic Limit row; Class/Structure row
    - mode: Loss of mechanical integrity in a LiF-rich interphase on lithium metal
      trigger: Plating of lithium metal against a LiF-enriched interphase
      consequence: The PNAS study finds that the mechanical integrity of LiF is easily compromised during plating, so LiF alone cannot protect the lithium. It finds that in situ repair of the interface by the electrolyte is the more critical determinant of electrode performance.
      severity: moderate
      source: he-pnas-2020
      where: Abstract
  side_effects:
    - text: In contact with a mineral acid the material gives off hydrogen fluoride gas, according to the safety sheet.
      affects: Operators and nearby equipment
      source: crystran-lif-msds
      where: Section 10.6
  handling:
    - text: Wear PVA gloves, a laboratory coat and safety goggles where chipping or dust may occur. Provide general mechanical and local exhaust ventilation, and wash hands immediately after handling.
      source: crystran-lif-msds
      where: Section 8.2
    - text: Avoid generating dust. Take up and containerise broken pieces for disposal, and do not let product enter drains.
      source: crystran-lif-msds
      where: Sections 6.1, 6.2, 6.3 and 7.1
    - text: Keep away from heat, foodstuffs, acids and strong bases, and protect the crystal from physical damage.
      source: crystran-lif-msds
      where: Sections 7.1 and 7.2
  mitigations:
    - text: Keep the crystal away from strong mineral acids and strong oxidising materials, which react with it.
      source: crystran-lif-msds
      where: Sections 10.1 and 10.5
uses:
  - application: optics-and-cameras
    device: Special UV optics and vacuum-ultraviolet windows
    example: Crystran says lithium fluoride is the material with the most extreme UV transmission of all, and that it transmits well into the vacuum ultraviolet at the hydrogen Lyman-alpha line (121 nm) and beyond.
    source: crystran-lif-datasheet
    where: Materials data text, applications paragraph
  - application: optics-and-cameras
    device: X-ray monochromator plates
    example: Crystran says lithium fluoride is used for X-ray monochromator plates, where its lattice spacing makes it the most useful analysis crystal.
    source: crystran-lif-datasheet
    where: Materials data text, applications paragraph
  - application: habitats-and-suits
    device: Thermoluminescent dosimeters (LiF:Mg,Ti)
    example: A 2021 paper on LiF:Mg,Ti detectors states that a fraction of the thermoluminescence signal comes from the supralinear dose range, and that prediction of TL efficiency is particularly important in space dosimetry.
    source: tl-pmc7840113
    where: Abstract
  - application: batteries
    device: Lithium-metal anode solid electrolyte interphase
    example: A 2020 PNAS study examines LiF-enriched interphases on lithium anodes, made artificially or from fluorinated electrolytes, and finds that LiF's mechanical integrity is easily compromised during plating.
    source: he-pnas-2020
    where: Abstract
supply:
  - subject: Lithium (feedstock, 2025 world mine production)
    producers:
      - country: Australia
        share_percent: 31.7
        year: 2025
      - country: China
        share_percent: 21.4
        year: 2025
      - country: Chile
        share_percent: 19.3
        year: 2025
      - country: Zimbabwe
        share_percent: 9.7
        year: 2025
      - country: Argentina
        share_percent: 7.9
        year: 2025
    critical_lists:
      - list: USGS 2025 List of Critical Minerals (lithium, used in rechargeable batteries)
        listed: true
      - list: EU critical raw materials list (Regulation (EU) 2024/1252, fifth list)
        listed: true
    recycling: 'USGS: construction of lithium battery recycling plants continued throughout 2025.'
    substitutes:
      - 'USGS: substitution for lithium compounds is possible in batteries, ceramics, greases and manufactured glass.'
    source: usgs-mcs2026-lithium
    where: World Mine Production and Reserves table, 2025 column (shares calculated by Space Mushroom as country value divided by the 290,000 t world total); Recycling; Substitutes
  - subject: Fluorspar (fluorine feedstock, 2025 world mine production)
    producers:
      - country: China
        share_percent: 60
        year: 2025
      - country: Mexico
        share_percent: 15
        year: 2025
      - country: Mongolia
        share_percent: 15
        year: 2025
      - country: South Africa
        share_percent: 4.1
        year: 2025
    critical_lists:
      - list: USGS 2025 List of Critical Minerals (fluorspar)
        listed: true
      - list: EU critical raw materials list (fluorspar)
        listed: true
    recycling: 'USGS: synthetic fluorspar may be produced from waste neutralization in uranium enrichment, petroleum alkylation and stainless-steel pickling, but undesirable impurities constrain its use.'
    substitutes:
      - 'USGS: fluosilicic acid has been used as an alternative to fluorspar in producing aluminum fluoride and hydrogen fluoride.'
    source: usgs-mcs2026-fluorspar
    where: World Mine Production and Reserves table, 2025 column (China 6,000, Mexico 1,500, Mongolia 1,500, South Africa 410 of a world total of 10,000 thousand tons; shares calculated by Space Mushroom); Recycling; Substitutes
documents:
  - title: 'Crystran: Lithium Fluoride (LiF) materials data sheet (PDF, data table and refractive index table)'
    type: datasheet
    url: https://www.crystran.com/wp-content/uploads/2025/09/lithium-fluoride-lif-data-sheet.pdf
    year: 2026
  - title: 'Crystran: Safety Data Sheet, Lithium Fluoride Optical Crystal (revision 2026, issued 6 July 2026)'
    type: sds
    url: https://www.crystran.com/wp-content/uploads/2025/09/lithium-fluoride-lif-msds.pdf
    year: 2026
  - title: 'USGS Mineral Commodity Summaries 2026: Lithium'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-lithium.pdf
    year: 2026
  - title: 'USGS Mineral Commodity Summaries 2026: Fluorspar'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-fluorspar.pdf
    year: 2026
  - title: Microdosimetric understanding of dose response and relative efficiency of thermoluminescence detectors (Radiat Prot Dosimetry 2021, open access)
    type: paper
    url: https://pmc.ncbi.nlm.nih.gov/articles/PMC7840113/
    year: 2021
  - title: 'He et al.: The intrinsic behavior of lithium fluoride in solid electrolyte interphases on lithium (PNAS 2020)'
    type: paper
    url: https://doi.org/10.1073/pnas.1911017116
    year: 2020
gaps:
  - No space, radiation-ageing, UV-ageing, outgassing (TML/CVCM) or atomic-oxygen result for lithium fluoride was found in a source we could open.
  - The molten-salt reactor role of LiF is not sourced in this file. The ORNL/OSTI record, the RSC and DOAJ article pages and the IPEN repository could not be opened in this run, so no LiF-BeF2 mixture figures are entered.
  - PubChem could not be read (bot check). Hazard data rest on one supplier safety data sheet (Crystran), and other suppliers' classifications are not checked.
  - 'Melting point differs: 848 C on the data sheet and 842 C on the safety sheet. The data sheet value is used.'
  - Dielectric constant is printed as 0.1 on the data sheet. That looks wrong for a fluoride, so it is not entered.
  - Knoop hardness is printed as 102 with a 600 g indenter, without a scale unit, so it is not entered.
  - Absorption coefficient 5.9 x 10-3 cm-1 at 4.3 µm and 300 K is printed on the data sheet but not entered; it can be added once the value is checked against the cited page.
  - 'Five benchmark names are kept as snake_case and may not be canonical: apparent_elastic_limit, reststrahlen_peak, refractive_index_temperature_coefficient, water_solubility and transmission_range.'
  - 'Wikipedia gives a lower water solubility and describes the crystals as hygroscopic. Neither is entered: Wikipedia is not used for values, and no supplier sheet read here confirms either point.'
  - The transmission curves are not read as numbers; the range is from the data table only.
  - Lithium and fluorspar supply shares are Space Mushroom calculations from the USGS 2025 production tables, not printed shares.
  - No media (photograph or drawing with a licence) was checked for this profile.
license: CC-BY-4.0
updated: '2026-10-26'
review:
  status: draft
  method: assistant
  checked_values: 17
  unreachable: 5
  caveats: 4
  note: 'Written by an AI assistant on 2026-10-26 from the Crystran data sheet and safety sheet (both read as PDF text), USGS Mineral Commodity Summaries 2026 for lithium and fluorspar, a 2021 open-access paper on TL detectors and a 2020 PNAS paper, read in the same run. Caveats: PubChem, OSTI, RSC, DOAJ and IPEN could not be opened; the molten-salt reactor use is not sourced; the Crystran dielectric constant is not entered.'
sources:
  crystran-lif-datasheet:
    title: 'Crystran: Lithium Fluoride (LiF) materials data sheet (data table, refractive index table, VUV transmission curve)'
    id: lithium-fluoride-lif-data-sheet.pdf (undated; pages 66 and 67)
    url: https://www.crystran.com/wp-content/uploads/2025/09/lithium-fluoride-lif-data-sheet.pdf
    year: 2026
    kind: datasheet
    license: supplier document, linked not reproduced
  crystran-lif-msds:
    title: 'Crystran: Safety Data Sheet, Lithium Fluoride Optical Crystal (REACH format, revision 2026)'
    id: Revision 2026, issued 6 July 2026; CAS 7789-24-4; EC 232-152-0
    url: https://www.crystran.com/wp-content/uploads/2025/09/lithium-fluoride-lif-msds.pdf
    year: 2026
    kind: datasheet
    license: supplier document, linked not reproduced
  usgs-mcs2026-lithium:
    title: Mineral Commodity Summaries 2026, Lithium (USGS)
    id: USGS MCS 2026, February 2026
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-lithium.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
  usgs-mcs2026-fluorspar:
    title: Mineral Commodity Summaries 2026, Fluorspar (USGS, Vanessa Londono)
    id: USGS MCS 2026, February 2026
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-fluorspar.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, list of 34 critical raw materials under Regulation (EU) 2024/1252)
    id: Regulation (EU) 2024/1252
    url: https://single-market-economy.ec.europa.eu/sectors/raw-materials/areas-specific-interest/critical-raw-materials_en
    year: 2024
    kind: web
    license: European Commission web page
  tl-pmc7840113:
    title: Microdosimetric understanding of dose response and relative efficiency of thermoluminescence detectors
    id: doi:10.1093/rpd/ncaa211 (Radiat Prot Dosimetry 192(2), 165-177, 2021; PMC7840113)
    url: https://pmc.ncbi.nlm.nih.gov/articles/PMC7840113/
    year: 2021
    kind: paper
    license: open access (Oxford University Press, PMC copy)
  he-pnas-2020:
    title: The intrinsic behavior of lithium fluoride in solid electrolyte interphases on lithium
    id: doi:10.1073/PNAS.1911017116 (PNAS 2020; He, Guo, Hobold, Gao, Gallant)
    url: https://doi.org/10.1073/pnas.1911017116
    year: 2020
    kind: paper
    license: MIT DSpace open access record; publisher terms apply
  wikipedia-lif:
    title: Lithium fluoride (Wikipedia article)
    id: en.wikipedia.org, accessed 2026-10-26; used for preparation route only
    url: https://en.wikipedia.org/wiki/Lithium_fluoride
    year: 2026
    kind: web
    license: CC BY-SA 4.0
story:
  recipe:
    line: Lithium fluoride is LiF, one lithium ion and one fluoride ion per formula unit, with a sodium-chloride-type structure. It is prepared from lithium hydroxide or lithium carbonate with hydrogen fluoride (Wikipedia). Crystran grows the optical crystal by the vacuum Stockbarger technique in ingots about 100 mm in diameter. Hydrogen fluoride, the fluorine source, is made from fluorspar, which USGS names as the feedstock for virtually all fluorine-bearing chemicals.
    parts:
      - name: Lithium
        symbol: Li
        role: The mobile ion. Lithium ions are the species that carry charge in a lithium-metal interphase and in the lithium salts that the material supplies.
      - name: Fluorine
        symbol: F
        role: The anion. Fluoride ions give the crystal its wide transmission in the ultraviolet and make it reactive with strong acids.
  risk_groups:
    - title: For people
      level: 1
      verdict: Harmful if swallowed or inhaled; irritating
      lead: The Crystran safety sheet (revision 2026) classes lithium fluoride as a Class 6.1 poison with H302, H315, H319 and H332, and gives an oral LD50 above 143 mg/kg in rats.
      points:
        - label: Dust
          line: The sheet gives an occupational limit of 2.5 mg/m3 as fluoride, as an 8 hour average, and says to avoid making dust.
        - label: Swallowed
          line: If swallowed, the material causes nausea, vomiting, stomach pains and diarrhoea, according to the sheet.
        - label: Scope
          line: Only the Crystran safety sheet was read. PubChem could not be opened, and other suppliers' classifications are not checked here.
    - title: If it fails
      lead: The failure results come from supplier data sheets and one interphase study. No flight failure record was read.
      points:
        - label: Cleavage
          line: The data sheet says the crystal cleaves easily on (100), and that polishing, particularly at steep radii, often causes surface rip-out.
        - label: Interphase
          line: The 2020 PNAS study finds that LiF in a lithium-metal interphase is easily broken during plating, so the electrolyte's repair of the interface matters more.
    - title: Handling and storage
      gap: The sheets give no storage temperature or humidity limit.
      points:
        - label: Protective equipment
          line: PVA gloves, a laboratory coat and safety goggles where chipping or dust may occur, with mechanical and local exhaust ventilation.
        - label: Incompatible materials
          line: Strong mineral acids and strong oxidising materials. Hydrogen fluoride gas forms in contact with a mineral acid.
  why: 'Lithium fluoride is a cubic crystal that Crystran supplies for the deepest ultraviolet optics. Its data sheet gives a refractive index of 1.392 at 0.6 µm, a transmission range of 0.12 to 6 µm, a density of 2.639 g/cc and a melting point of 848 °C. Its use is driven by ultraviolet transmission, X-ray monochromators and thermoluminescent dosimetry, rather than by mechanical strength: the crystal cleaves easily and its apparent elastic limit is 11.2 MPa.'
  uses:
    - where: Vacuum-ultraviolet optics
      line: Crystran says lithium fluoride has the most extreme UV transmission of all its materials, and transmits into the vacuum ultraviolet at the 121 nm hydrogen Lyman-alpha line and beyond.
    - where: X-ray monochromators
      line: Crystran says its lattice spacing makes lithium fluoride the most useful analysis crystal for X-ray monochromator plates.
    - where: Thermoluminescent dosimetry
      line: A 2021 open-access paper on LiF:Mg,Ti detectors says that prediction of their thermoluminescence efficiency is particularly important in space dosimetry.
    - where: Lithium-metal battery interphase
      line: A 2020 PNAS study looks at LiF-enriched interphases on lithium anodes, which are formed either artificially or from fluorinated electrolytes, and finds that LiF's mechanical integrity is easily compromised.
  can_do:
    - label: Range
      value: 0.12 to 6 µm
      line: Crystran's data table gives a transmission range of 0.12 to 6 µm, and says the material reaches the 121 nm Lyman-alpha line.
    - label: Refraction
      value: '1.392'
      line: Refractive index 1.392 at 0.6 µm and 1.3266 at 5 µm, per the Crystran data table and its refractive index table.
    - label: Heat
      value: 848 °C
      line: Melting point 848 °C on the data sheet (842 °C on the safety sheet). Thermal conductivity 11.3 W/(m·K) at 314 K.
    - label: Stiffness
      value: 64.97 GPa
      line: Young's modulus 64.97 GPa, shear modulus 55.14 GPa and bulk modulus 62.03 GPa, from the Crystran data table.
  compare: 'This profile does not compare numbers with the other fluorides in this collection, because their sheets were not read in this run. Crystran describes lithium fluoride as having the most extreme UV transmission of all its materials, and its own sheet shows that it is soft and easily cleaved: its apparent elastic limit is 11.2 MPa and it cleaves on (100). The sources read give no side-by-side ground or space test.'
  compare_rows:
    - label: Heat conduction
      benchmark: thermal_conductivity
    - label: Thermal expansion
      benchmark: cte
    - label: Stiffness
      benchmark: elastic_modulus
  handling:
    - Wear PVA gloves and goggles where chipping or dust may occur, and avoid making dust when cutting, grinding or cleaning.
    - Keep the crystal away from strong mineral acids and strong oxidising materials, which give off hydrogen fluoride gas on reaction.
    - Do not let product enter drains, and take up broken pieces into containers for disposal.
  good_for:
    - Vacuum-ultraviolet optics that must transmit to 121 nm (Crystran).
    - X-ray monochromator plates, where its lattice spacing suits analysis (Crystran).
    - Thermoluminescent dosimetry with LiF:Mg,Ti detectors, where space dosimetry relies on predicting their response (2021 paper).
  watch_out:
    - Cleavage. The crystal cleaves easily on (100), and polishing at steep radii can cause rip-out (Crystran).
    - Acids. Strong mineral acids and strong oxidising materials react with it and give off hydrogen fluoride (safety sheet).
    - Solubility. It dissolves to 0.27 g per 100 g of water at 20 C, and the safety sheet lists it as hazardous to drinking water.
    - No space test. No flight, radiation-ageing or outgassing result for lithium fluoride was found in the sources read.
  verdict: Lithium fluoride is Crystran's choice for the deepest ultraviolet optics, with a 0.12 to 6 µm transmission range and a reach to 121 nm. Its brittleness and acid sensitivity are the trade-off. The thermoluminescent and battery uses rest on papers rather than flight data, and this profile does not establish its behaviour in orbit.