Ge2Sb2Te5 (GST225) phase-change memory alloy GST225

spore: profile
id: ge2sb2te5
spore_version: 0.2
family: phase-change-chalcogenides
name: Ge2Sb2Te5 (GST225) phase-change memory alloy
abbreviation: GST225
role: phase-change memory material
category: electronics
type: memory-materials
summary: |
  Ge2Sb2Te5 (GST225) is a germanium-antimony-tellurium alloy in the atomic ratio 2:2:5. It switches between an amorphous, high-resistance state and a crystalline, low-resistance state. Zhang et al. give a crystallization temperature of about 175°C and a melting temperature of about 610°C for the thin film, while a globalsino data table gives 151 to 174 °C and 632 °C for the metastable fcc phase. Zaytseva et al. report that the resistivity of a sputtered film falls by an order of magnitude when annealed to 168 °C.
best_for: Phase-change memory cells that need a large change in electrical resistance between the amorphous and the crystalline state (Zhang et al. give 1.7 x 10^8 Ω/sq as deposited and 165 Ω/sq after 400 °C annealing)
weakest_at: 'Heat tolerance of the stored amorphous state: crystallization is reported from 151 to 174 °C (globalsino) or about 175 °C (Zhang et al.), and no radiation or space test of the alloy was read in this run'
identity:
  formula: Ge2Sb2Te5 (Ge:Sb:Te = 2:2:5), a chalcogenide alloy of germanium, antimony and tellurium; general form GexSbyTez
  crystal_system: Amorphous as deposited; metastable fcc (NaCl-type) and stable hcp (trigonal) crystal forms
  space_group: Fm-3m (metastable fcc); P-3m1 (stable hcp)
  source: globalsino
  where: Table 3161, Ge2Sb2Te5 phase rows and their notes; Zaytseva et al. (2020), Section 1 (hexagonal structure P-3m1)
tags:
  environments: []
  stresses: []
  applications:
    - electronics-and-chips
    - optics-and-cameras
properties:
  - benchmark: atomic_density
    label: Atomic density, amorphous Ge2Sb2Te5
    value: 0.03
    unit: atom·Å⁻³
    scope: material
    conditions:
      phase: amorphous
      unit_in_source: atom·Å⁻³
    method: Value printed in the structural properties table of the Globalsino page (Table 3161)
    status: ground
    source: globalsino
    where: Table 3161, amorphous Ge2Sb2Te5 row, Atomic density column
  - benchmark: atomic_density
    label: Atomic density, metastable fcc Ge2Sb2Te5
    value: 0.0335
    unit: atom·Å⁻³
    scope: material
    conditions:
      phase: metastable fcc (NaCl-type, Fm-3m)
      unit_in_source: atom·Å⁻³
    method: Value printed in the structural properties table of the Globalsino page (Table 3161)
    status: ground
    source: globalsino
    where: Table 3161, metastable fcc Ge2Sb2Te5 row, Atomic density column
  - benchmark: density
    label: Density, stable hcp Ge2Sb2Te5
    value: 6300
    unit: kg·m⁻³
    scope: material
    conditions:
      phase: stable hcp (trigonal, P-3m1)
      unit_in_source: kg·m⁻³
    method: Value printed in the note of the stable hcp row of the Globalsino page (Table 3161); the page gives no mass density for the amorphous or fcc phases
    status: ground
    source: globalsino
    where: Table 3161, note for the stable hcp Ge2Sb2Te5 row
  - benchmark: melting_point
    label: Melting point, metastable fcc Ge2Sb2Te5
    value: 632
    unit: °C
    scope: material
    conditions:
      phase: metastable fcc
      pressure: not stated
    method: Value printed in the melting point column of Table 3161 on the Globalsino page
    status: ground
    source: globalsino
    where: Table 3161, metastable fcc Ge2Sb2Te5 row, Melting point column
  - benchmark: melting_point
    label: Melting temperature of the thin film (printed as about)
    value: 610
    unit: °C
    scope: material
    conditions:
      form: thin film
      phase: not specified in the abstract
      printed_as: about 610°C
    method: Value printed in the abstract of the Zhang et al. paper; the abstract gives it as approximate
    status: ground
    source: zhang-cpl
    where: Abstract
  - benchmark: crystallization_temperature
    label: Crystallization temperature range, metastable fcc Ge2Sb2Te5
    value: 151
    value_high: 174
    bound: range
    unit: °C
    scope: material
    conditions:
      phase: amorphous to metastable fcc
      heating: not stated
    method: Range printed in the crystallization temperature column of Table 3161 on the Globalsino page
    status: ground
    source: globalsino
    where: Table 3161, metastable fcc Ge2Sb2Te5 row, Crystallization temperature column
  - benchmark: crystallization_temperature
    label: Crystallization temperature of the thin film (printed as about)
    value: 175
    unit: °C
    scope: material
    conditions:
      transition: amorphous to crystalline
      form: thin film
      printed_as: about 175°C
    method: Value printed in the abstract of the Zhang et al. paper
    status: ground
    source: zhang-cpl
    where: Abstract
  - benchmark: crystallization_temperature
    label: Resistivity inflection point during heating
    value: 168
    unit: °C
    scope: material
    conditions:
      heating_rate: 5 °C/min
      atmosphere: argon
      form: DC magnetron sputtered thin film
    method: Temperature of the inflection point on the resistivity-temperature curve, printed in the abstract and Section 3 of the Zaytseva et al. paper
    status: ground
    source: zaytseva2020
    where: Abstract; Section 3 (Results and discussion)
  - benchmark: crystallization_temperature
    label: End of the resistivity drop during heating
    value: 183
    unit: °C
    scope: material
    conditions:
      heating_rate: 5 °C/min
      atmosphere: argon
      form: DC magnetron sputtered thin film
    method: Temperature at which the resistivity drop ends, printed in the abstract of the Zaytseva et al. paper
    status: ground
    source: zaytseva2020
    where: Abstract; Section 3 (Results and discussion)
  - benchmark: electrical_conductivity
    label: Electrical conductivity, amorphous Ge2Sb2Te5
    value: 3
    unit: Ω⁻¹·m⁻¹
    scope: material
    conditions:
      phase: amorphous
      unit_in_source: Ω⁻¹·m⁻¹
    method: Value printed in the note of the amorphous Ge2Sb2Te5 row of Table 3161 on the Globalsino page
    status: ground
    source: globalsino
    where: Table 3161, note for the amorphous Ge2Sb2Te5 row (electric conductivity 3 Ω-1-m-1)
  - benchmark: electrical_conductivity
    label: Electrical conductivity, metastable fcc Ge2Sb2Te5
    value: 2770
    unit: Ω⁻¹·m⁻¹
    scope: material
    conditions:
      phase: metastable fcc
      unit_in_source: Ω⁻¹·m⁻¹
    method: Value printed in the note of the metastable fcc row of Table 3161 on the Globalsino page
    status: ground
    source: globalsino
    where: Table 3161, note for the metastable fcc Ge2Sb2Te5 row
  - benchmark: thermal_conductivity
    label: Thermal conductivity, amorphous Ge2Sb2Te5
    value: 0.2
    unit: W/K-m
    scope: material
    conditions:
      phase: amorphous
      unit_in_source: W/K-m
    method: Value printed in the note of the amorphous Ge2Sb2Te5 row of Table 3161 (unit printed as W/K-m)
    status: ground
    source: globalsino
    where: Table 3161, note for the amorphous Ge2Sb2Te5 row
  - benchmark: thermal_conductivity
    label: Thermal conductivity, metastable fcc Ge2Sb2Te5
    value: 0.5
    unit: W/K-m
    scope: material
    conditions:
      phase: metastable fcc
      unit_in_source: W/K-m
    method: Value printed in the note of the metastable fcc row of Table 3161 (unit printed as W/K-m)
    status: ground
    source: globalsino
    where: Table 3161, note for the metastable fcc Ge2Sb2Te5 row
  - benchmark: thermal_conductivity
    label: Thermal conductivity, stable hcp Ge2Sb2Te5
    value: 1.59
    unit: W·m⁻¹·K⁻¹
    scope: material
    conditions:
      phase: stable hcp
      unit_in_source: W•m-1•K-1
    method: Value printed in the note of the stable hcp row of Table 3161 on the Globalsino page
    status: ground
    source: globalsino
    where: Table 3161, note for the stable hcp Ge2Sb2Te5 row
  - benchmark: activation_energy_crystallization
    label: Activation energy of crystallization, amorphous Ge2Sb2Te5
    value: 3.636
    unit: eV
    scope: material
    conditions:
      phase: amorphous
      unit_in_source: eV
    method: Value printed in the note of the amorphous Ge2Sb2Te5 row of Table 3161
    status: ground
    source: globalsino
    where: Table 3161, note for the amorphous Ge2Sb2Te5 row
  - benchmark: band_gap
    label: Band gap, amorphous Ge2Sb2Te5
    value: 0.7
    value_high: 1
    bound: range
    unit: eV
    scope: material
    conditions:
      phase: amorphous
      unit_in_source: eV
    method: Range printed in the note of the amorphous Ge2Sb2Te5 row of Table 3161
    status: ground
    source: globalsino
    where: Table 3161, note for the amorphous Ge2Sb2Te5 row (Band gap 0.7 - 1.0 eV)
  - benchmark: elastic_modulus
    label: Young's modulus, stable hcp Ge2Sb2Te5
    value: 58.7
    unit: GPa
    scope: material
    conditions:
      phase: stable hcp
      unit_in_source: GPa
    method: Value printed in the note of the stable hcp row of Table 3161 on the Globalsino page
    status: ground
    source: globalsino
    where: Table 3161, note for the stable hcp Ge2Sb2Te5 row
  - benchmark: cte
    label: Thermal expansion coefficient, stable hcp Ge2Sb2Te5
    value: 17.4
    unit: ppm/K
    scope: material
    conditions:
      phase: stable hcp
      unit_in_source: 17.4 x 10⁻⁶ K⁻¹ (equal to ppm/K)
    method: Value printed in the note of the stable hcp row of Table 3161 on the Globalsino page
    status: ground
    source: globalsino
    where: Table 3161, note for the stable hcp Ge2Sb2Te5 row
  - benchmark: poissons_ratio
    label: Poisson's ratio, stable hcp Ge2Sb2Te5
    value: 0.3
    unit: '-'
    scope: material
    conditions:
      phase: stable hcp
    method: Value printed in the note of the stable hcp row of Table 3161 on the Globalsino page
    status: ground
    source: globalsino
    where: Table 3161, note for the stable hcp Ge2Sb2Te5 row
  - benchmark: sheet_resistance
    label: Sheet resistance after 400 °C annealing
    value: 165
    unit: Ω/sq
    scope: material
    conditions:
      annealing: 400 °C
      phase: hexagonal close-packed (hcp) per the abstract's transition sequence
      unit_in_source: Ω/sq
    method: Value printed in the abstract of the Zhang et al. paper, where the page calls it electrical resistance
    status: ground
    source: zhang-cpl
    where: Abstract
corrosion:
  - environment: Aqueous nitric acid (wet etch test on Ge2Sb2Te5 films)
    headline: Nitric acid is the only acid on the globalsino list that etches Ge2Sb2Te5.
    effect: Both alpha- and c-Ge2Sb2Te5 can only be etched by aqueous nitric acid (HNO3). The page says they cannot be etched by oxalic acid, perchloric acid, acetic acid, sulphuric acid, phosphoric acid or hydrochloric acid. The page gives this as an etch property, not as a corrosion rate.
    rating: moderate
    conditions:
      acid: HNO3 aqueous solution
      concentration: not stated
      temperature: not stated
    source: globalsino
    where: Table 3161, note for the Ge2Sb2Te5 row
  - environment: Oxalic, perchloric, acetic, sulphuric, phosphoric and hydrochloric acids
    headline: The globalsino page says Ge2Sb2Te5 cannot be etched by these six acids.
    effect: The same note lists oxalic acid (H2C2O4), perchloric acid (HClO4), acetic acid (CH3COOH), sulphuric acid (H2SO4), phosphoric acid (H3PO4) and hydrochloric acid (HCl) as not etching the alpha- and c-Ge2Sb2Te5 phases. No corrosion rate was recorded for them.
    rating: low
    conditions:
      basis: etch test as printed; concentration and temperature not stated
    source: globalsino
    where: Table 3161, note for the Ge2Sb2Te5 row
  - environment: Room-temperature storage (stated for Ge2Sb2Te5)
    headline: The globalsino page says Ge2Sb2Te5 is stable at room temperature for more than 10 years.
    effect: The globalsino table note states that Ge2Sb2Te5 is stable at room temperature for more than 10 years. No humidity, atmosphere or test method is given for this statement.
    rating: low
    conditions:
      temperature: room temperature (no value printed)
      atmosphere: not stated
      basis: statement in the table note
    source: globalsino
    where: Table 3161, note for the amorphous Ge2Sb2Te5 row
risks:
  hazards:
    - text: 'Germanium (element, PubChem CID 6326954): PubChem''s GHS classification gives the signal word Danger and pictograms GHS02 (flammable) and GHS08 (health hazard). Hazard statements printed: 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. These describe the element, not the Ge2Sb2Te5 alloy.'
      ghs:
        - H228
        - H361
        - H373
        - H412
      source: pubchem-ge
      where: GHS Classification section (aggregated company notifications), CID 6326954
    - text: 'Tellurium (element, PubChem CID 6327182): the ECHA C&L Inventory record in PubChem gives the signal word Danger and hazard statements H301 Toxic if swallowed; H317 May cause an allergic skin reaction; H319 Causes serious eye irritation; H332 Harmful if inhaled; H335 May cause respiratory irritation; H360 May damage fertility or the unborn child; H360Df May damage the unborn child; Suspected of damaging fertility; H362 May cause harm to breast-fed children; H413 May cause long lasting harmful effects to aquatic life. These describe the element, not the Ge2Sb2Te5 alloy.'
      ghs:
        - H301
        - H317
        - H319
        - H332
        - H335
        - H360
        - H360Df
        - H362
        - H413
      source: pubchem-te
      where: GHS Classification section, ECHA C&L Inventory aggregated notifications, CID 6327182
    - text: 'Antimony (element, PubChem CID 5354495): the ECHA C&L Inventory record (EC 231-146-5) in PubChem gives the signal word Danger and pictograms Acute Toxic, Irritant, Health Hazard and Environmental Hazard. Hazard statements printed: H301 Toxic if swallowed; H302 Harmful if swallowed; H332 Harmful if inhaled; H351 Suspected of causing cancer; H373 "May causes damage to organs through prolonged or repeated exposure"; H411 Toxic to aquatic life with long lasting effects. These describe the element, not the Ge2Sb2Te5 alloy.'
      ghs:
        - H301
        - H302
        - H332
        - H351
        - H373
        - H411
      source: pubchem-sb
      where: GHS Classification section, ECHA C&L Inventory record, CID 5354495
  failure_risks:
    - mode: Crystallization of the amorphous (high-resistance) state
      trigger: Heating of the film into the crystallization range, 151 to 174 °C (globalsino) or about 175 °C (Zhang et al.)
      consequence: The amorphous state turns crystalline and its resistance falls. Zaytseva et al. report that the resistivity of a sputtered film falls by an order of magnitude when annealed to 168 °C, and that crystallites of up to 7 nm were seen in the TEM at that point. The sources give no retention time at a stated temperature.
      severity: moderate
      source: zaytseva2020
      where: Abstract; Section 3 (Results and discussion)
    - mode: Melting of the crystalline film
      trigger: Heating to the melting point, 632 °C for the metastable fcc phase (globalsino) or about 610 °C for the thin film (Zhang et al.)
      consequence: The film melts. The sources give the melting temperatures only and no consequence test for a memory cell.
      severity: moderate
      source: globalsino
      where: Table 3161, Melting point column
  side_effects: []
  handling: []
  mitigations: []
uses:
  - application: electronics-and-chips
    device: Rewritable phase-change memory cells
    example: Zaytseva et al. state that GST materials are widely used as rewritable storage media. The same paper says crystallization is the slowest operation of a phase-change device and so limits its overall performance.
    source: zaytseva2020
    where: Section 1 (Introduction)
  - application: electronics-and-chips
    device: Multi-level non-volatile memory (research direction)
    example: Zaytseva et al. say a new type of non-volatile memory is being developed that would store several levels in one cell by using intermediate phases between the fully crystalline and fully amorphous states.
    source: zaytseva2020
    where: Section 1 (Introduction)
  - application: optics-and-cameras
    device: Configurable photonic devices (phase change optical metamaterials, metasurfaces, optoelectronic displays)
    example: Zaytseva et al. say GST alloys are very attractive for configurable photonic applications such as phase change optical metamaterials, metasurfaces and optoelectronic displays.
    source: zaytseva2020
    where: Section 1 (Introduction)
  - application: electronics-and-chips
    device: Intel and Micron 3D XPoint memory (history)
    example: Wikipedia's timeline says Intel and Micron announced 3D Xpoint memory in which a phase-change alloy is the storage part of a memory cell. That entry does not name Ge2Sb2Te5.
    source: wikipedia-pcm
    where: Timeline section
supply:
  - subject: Germanium
    abundance: Not read in this run.
    producers: []
    critical_lists:
      - list: 'USGS 2025 List of Critical Minerals (entry: Germanium, used in fiberoptics, semiconductors and night vision)'
        listed: true
    recycling: 'USGS: the United States has the capability to recycle new (preconsumer) and old (postconsumer) germanium.'
    substitutes:
      - 'USGS: silicon or gallium arsenide substitute for germanium in certain electronic applications.'
    source: usgs-mcs2026-germanium
    where: 'Domestic Production and Use, Import Sources (2021–24) for germanium metal: China 41%, Belgium 27%, Germany 25%, Russia 3%; World Refinery Production and Reserves (China the leading producer, no production shares printed); Recycling; Substitutes. Critical list: USGS 2025 list page.'
  - subject: Antimony
    abundance: Not read in this run.
    producers: []
    critical_lists:
      - list: 'USGS 2025 List of Critical Minerals (entry: Antimony, used in lead-acid batteries and flame retardants)'
        listed: true
    recycling: 'USGS: the bulk of secondary antimony is recovered at secondary lead smelters as antimonial lead.'
    substitutes: []
    source: usgs-mcs2026-antimony
    where: 'World Mine Production and Reserves, mine production 2025e in metric tons of antimony content: China 40,000; Russia 32,000; Tajikistan 22,000; Bolivia 5,000; world total (rounded) 110,000. Recycling; Critical list: USGS 2025 list page.'
  - subject: Tellurium
    abundance: Not read in this run.
    producers:
      - country: China
        share_percent: 80
        year: 2025
    critical_lists:
      - list: 'USGS 2025 List of Critical Minerals (entry: Tellurium, used in solar cells, to strengthen steel and copper, and to produce rubber, microchips and laser diodes)'
        listed: true
    recycling: 'USGS: tellurium was recycled from CdTe solar cells in the United States, but the quantity recycled was limited.'
    substitutes:
      - 'USGS: several materials can replace tellurium in most of its uses, usually with losses in efficiency or product characteristics.'
    source: usgs-mcs2026-tellurium
    where: 'Events, Trends, and Issues: China accounted for 80% of estimated global production in 2025; Recycling; Substitutes; Critical list: USGS 2025 list page.'
documents:
  - title: 'Globalsino: Ge2Sb2Te5 (GST) structural and property data, Table 3161'
    type: database
    url: https://www.globalsino.com/EM/page3161.html
  - title: Zhang et al., Structure and Electrical Properties of Ge2Sb2Te5 Thin Film Used for Ovonic Unified Memory (Chinese Physics Letters website)
    type: paper
    url: https://cpl.iphy.ac.cn/article/id/37700
  - title: Zaytseva et al., Structure of Ge2Sb2Te5 thin films near the inflection point of the resistivity temperature dependence, Chalcogenide Letters 17(2), 41-47
    type: paper
    url: https://www.chalcogen.ro/41_ZaytsevaY.pdf
    year: 2020
  - title: 'Wikipedia: Phase-change memory (composition and timeline)'
    type: database
    url: https://en.wikipedia.org/wiki/Phase-change_memory
  - title: 'USGS Mineral Commodity Summaries 2026: Germanium'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-germanium.pdf
    year: 2026
  - title: 'USGS Mineral Commodity Summaries 2026: Antimony'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-antimony.pdf
    year: 2026
  - title: 'USGS Mineral Commodity Summaries 2026: Tellurium'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-tellurium.pdf
    year: 2026
  - title: 'USGS: About the 2025 List of Critical Minerals (final list, November 6, 2025)'
    type: report
    url: https://www.usgs.gov/programs/mineral-resources-program/science/about-2025-list-critical-minerals
    year: 2025
  - title: 'PubChem: Germanium (CID 6326954), GHS Classification'
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/compound/6326954
  - title: 'PubChem: Tellurium (CID 6327182), GHS Classification (ECHA C&L Inventory)'
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/compound/6327182
  - title: 'PubChem: Antimony (CID 5354495), GHS Classification (ECHA C&L Inventory)'
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/compound/5354495
gaps:
  - 'Alloy-level hazards: no safety data sheet for the Ge2Sb2Te5 alloy itself was read. The LTS Research Laboratories sheet (ltschem.com/msds/Ge2Sb2Te5.pdf) and the American Elements listing returned HTTP 403 to the fetch tool, so they were not used. risks.hazards gives the PubChem GHS records for germanium, tellurium and antimony only; those describe the elements, not the alloy.'
  - No CAS number, UNS, EN, ASTM or trade designation for Ge2Sb2Te5 was read, so identity.designations is left out.
  - No radiation test (total dose, single-event effects, displacement damage) and no space flight result for Ge2Sb2Te5 was opened. The brief's radiation-tolerant memory claim is not supported by any page read in this run.
  - 'Optane: Wikipedia says Intel and Micron used a phase-change alloy for 3D XPoint but does not name Ge2Sb2Te5, and no Optane-specific source was read.'
  - 'Melting point and crystallization temperature disagree between sources: 632 °C (globalsino, fcc phase) against about 610 °C (Zhang et al.), and 151 to 174 °C against about 175 °C. Both are recorded; no source read resolves the difference.'
  - Resistivity contrast as a ratio, and resistivity in Ω·cm, were not stated on any page read. Zaytseva et al. give an order-of-magnitude fall at 168 °C; Zhang et al. give sheet resistances only.
  - Switching speed and write energy were not read in this run.
  - Atomic weights of germanium, antimony and tellurium were not read, so story.recipe.parts has no atomic_weight.
  - Specific heat is printed only as a volumetric heat capacity (J/K-m3). It is not converted to J/(kg·K), and no mass-based specific heat was read.
  - Mass density of the amorphous and fcc phases was not read; the globalsino table gives only atomic density (atom·Å⁻³).
  - Sheet resistance (Zhang et al.) and electrical conductivity (globalsino) are reported for different samples and conditions and are not converted into each other.
  - A separate passage of the globalsino page gives 3.66 eV for the activation energy of crystallization, which differs from the 3.636 eV in the table. Only the table value is recorded.
  - 'Corrosion: only the acid etch note and the room-temperature storage statement were read. No humidity, oxidation or thermal ageing data for Ge2Sb2Te5 were found.'
  - 'Supply: germanium and antimony production shares are not printed in the USGS summaries read; the germanium shares given are import shares. Crustal abundances of germanium, antimony and tellurium were not read. EU critical raw materials list was not read.'
  - Media (images) were not checked for licence and are left out of this profile.
  - The Zhang et al. page does not print a publication year or volume; the journal is taken from the website domain (cpl.iphy.ac.cn).
  - Hardness, refractive index and the band gap of the crystalline phases were not found in the sources read.
  - The globalsino values come from a flattened table; they were checked against the raw HTML text of the page, but no datasheet or second database confirmed them.
sources:
  globalsino:
    title: 'Globalsino: Ge2Sb2Te5 (GST) structural and property data, Table 3161'
    id: globalsino page3161
    url: https://www.globalsino.com/EM/page3161.html
    kind: database
    license: page content, cited not reproduced
  zhang-cpl:
    title: Structure and Electrical Properties of Ge2Sb2Te5 Thin Film Used for Ovonic Unified Memory
    id: Chinese Physics Letters website, article 37700; authors ZHANG Ting, LIU Bo, XIA Ji-Lin, SONG Zhi-Tang, FENG Song-Lin, CHEN Bomy
    url: https://cpl.iphy.ac.cn/article/id/37700
    kind: paper
    license: page content, cited not reproduced
  zaytseva2020:
    title: Structure of Ge2Sb2Te5 thin films near the inflection point of the resistivity temperature dependence
    id: Chalcogenide Letters 17(2), 41-47 (February 2020); authors Y. Zaytseva et al.
    url: https://www.chalcogen.ro/41_ZaytsevaY.pdf
    year: 2020
    kind: paper
    license: journal PDF, cited not reproduced
  wikipedia-pcm:
    title: Phase-change memory
    id: Wikipedia, English
    url: https://en.wikipedia.org/wiki/Phase-change_memory
    kind: web
    license: CC BY-SA 4.0 (cited, not reproduced)
  usgs-mcs2026-germanium:
    title: Mineral Commodity Summaries 2026, Germanium
    id: USGS MCS 2026
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-germanium.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
  usgs-mcs2026-antimony:
    title: Mineral Commodity Summaries 2026, Antimony
    id: USGS MCS 2026
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-antimony.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
  usgs-mcs2026-tellurium:
    title: Mineral Commodity Summaries 2026, Tellurium
    id: USGS MCS 2026
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-tellurium.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
  usgs-crit2025:
    title: About the 2025 List of Critical Minerals (USGS, final list, November 6, 2025)
    id: USGS 2025 List of Critical Minerals
    url: https://www.usgs.gov/programs/mineral-resources-program/science/about-2025-list-critical-minerals
    year: 2025
    kind: report
    license: public domain (USGS)
  pubchem-ge:
    title: 'PubChem: Germanium (CID 6326954), GHS Classification'
    id: PubChem CID 6326954
    url: https://pubchem.ncbi.nlm.nih.gov/compound/6326954
    kind: database
    license: public domain (NCBI PubChem); GHS data are aggregated from submitter notifications
  pubchem-te:
    title: 'PubChem: Tellurium (CID 6327182), GHS Classification (ECHA C&L Inventory)'
    id: PubChem CID 6327182
    url: https://pubchem.ncbi.nlm.nih.gov/compound/6327182
    kind: database
    license: public domain (NCBI PubChem); GHS data are aggregated from submitter notifications
  pubchem-sb:
    title: 'PubChem: Antimony (CID 5354495), GHS Classification (ECHA C&L Inventory)'
    id: PubChem CID 5354495
    url: https://pubchem.ncbi.nlm.nih.gov/compound/5354495
    kind: database
    license: public domain (NCBI PubChem); GHS data are aggregated from submitter notifications
license: CC-BY-4.0
updated: '2026-11-01'
review:
  status: draft
  method: assistant
  checked_values: 20
  unreachable: 2
  caveats: 3
  note: Written by an AI assistant on 2026-11-01 from pages fetched in this run. The hazards are PubChem GHS records for germanium, tellurium and antimony, read in a later pass; the alloy's own safety sheets (ltschem.com and americanelements.com) returned HTTP 403. The zhang-cpl and globalsino values were checked against the page text and the raw HTML; the Zaytseva values were checked against the extracted PDF text.
story:
  recipe:
    line: Ge2Sb2Te5 is an alloy of germanium, antimony and tellurium in the atomic ratio 2:2:5 (Wikipedia). Zaytseva et al. report that the composition of their sputtered thin film was close to Ge2Sb2Te5 by X-ray microanalysis, and the same paper describes the films as deposited by DC magnetron sputtering at room temperature.
    parts:
      - name: Germanium
        symbol: Ge
        role: Sits in the crystal lattice with antimony and vacancies in the metastable fcc phase, and has shorter, stronger bonds in the amorphous phase.
      - name: Antimony
        symbol: Sb
        role: Shares the cation sites with germanium in the crystal, and excess antimony forms conductive filaments in the globalsino notes.
      - name: Tellurium
        symbol: Te
        role: Forms one sublattice in the metastable fcc structure and the Te-Sb-Te-Ge-Te layers of the stable hcp structure.
  risk_groups:
    - title: For people
      level: 0
      verdict: Alloy classification not found; element records listed
      lead: No safety data sheet for the Ge2Sb2Te5 alloy itself was read in this run (two sheets returned access errors). The hazards in risks.hazards are the PubChem GHS records for its three elements.
      points:
        - label: Components
          line: The alloy is made of germanium, antimony and tellurium. Each element has a PubChem GHS record listed under risks.hazards, and each record describes the element, not the alloy.
    - title: If a film is heated
      lead: These results come from laboratory heating of thin films, not from field incidents.
      points:
        - label: Crystallization
          line: The globalsino table gives a crystallization temperature of 151 to 174 °C, and Zhang et al. give about 175 °C. Above this range the amorphous state turns crystalline and its resistance falls.
        - label: Melting
          line: The globalsino table gives a melting point of 632 °C for the metastable fcc phase. Zhang et al. give about 610 °C for the thin film. The two values differ and both are recorded.
    - title: Handling and storage
      points:
        - label: Storage
          line: The globalsino table note states that Ge2Sb2Te5 is stable at room temperature for more than 10 years. No atmosphere or humidity condition is given.
        - label: Heating limit
          line: Keep film process and storage temperatures below the 151 °C lower limit of the crystallization range given in the globalsino table.
  why: Ge2Sb2Te5 (GST225) is the phase-change alloy used as the storage element in rewritable phase-change memory. It switches between an amorphous state and a crystalline state, and the two states have very different electrical resistance. Zaytseva et al. describe GST materials as the basis of rewritable storage media, and a fast, reversible transition between phases is the operating principle of phase-change devices.
  uses:
    - where: Phase-change memory
      line: Zaytseva et al. state that GST materials are widely used as rewritable storage media. The same paper notes that crystallization is the slowest step in a phase-change device, so it limits overall device performance.
    - where: Multi-level memory (research direction)
      line: Zaytseva et al. say a new type of non-volatile memory is being developed that stores several levels in one cell, using phases between the fully crystalline and fully amorphous states.
    - where: Configurable photonics
      line: Zaytseva et al. say GST alloys are very attractive for configurable photonic applications, including phase change optical metamaterials, metasurfaces and optoelectronic displays.
    - where: 3D XPoint (history)
      line: Wikipedia's timeline says Intel and Micron announced 3D XPoint memory in which a phase-change alloy is the storage part of a memory cell. That entry does not name Ge2Sb2Te5, and no Optane source was read in this run.
  can_do:
    - label: Resistance contrast
      benchmark: sheet_resistance
      line: Zhang et al. report a sheet resistance of 1.7 x 10^8 Ω/sq for the as-deposited film, and 165 Ω/sq after annealing at 400 °C. The page prints the first value with its exponent as a superscript.
    - label: Melting point
      benchmark: melting_point
      line: The globalsino table gives a melting point of 632 °C for the metastable fcc phase. Zhang et al. give about 610 °C for the thin film.
    - label: Crystallization
      benchmark: crystallization_temperature
      line: The globalsino table gives a crystallization range of 151 to 174 °C. Zhang et al. give about 175 °C. Zaytseva et al. place a resistivity inflection at 168 °C and the end of the resistivity drop at 183 °C, with heating at 5 °C/min.
    - label: Storage
      benchmark: sheet_resistance
      line: The globalsino table note states that the alloy is stable at room temperature for more than 10 years. The statement gives no test method.
  compare: 'No other memory material was compared in this run. Within this one alloy, the two phases differ sharply in electrical conduction: the globalsino table gives an electrical conductivity of 3 Ω⁻¹·m⁻¹ for the amorphous phase and 2770 Ω⁻¹·m⁻¹ for the metastable fcc phase, and Zhang et al. give sheet resistances of 1.7 x 10^8 Ω/sq as deposited and 165 Ω/sq after 400 °C annealing. These are different samples and conditions, so the figures are not converted into each other.'
  compare_rows:
    - label: Melting point
      benchmark: melting_point
    - label: Crystallization temperature
      benchmark: crystallization_temperature
    - label: Electrical conductivity
      benchmark: electrical_conductivity
  handling:
    - No handling data (safety data sheet or GHS record) for the alloy was read in this run.
    - Heating a film into the crystallization range from about 151 °C changes its state, so keep process and storage temperatures below that range.
    - The globalsino table note says the alloy is stable at room temperature for more than 10 years. No humidity or atmosphere condition is given for that statement.
  good_for:
    - Two-state switching. Zhang et al. report 1.7 x 10^8 Ω/sq as deposited and 165 Ω/sq after 400 °C annealing, which is the contrast a memory cell reads.
    - Photonic switching research. Zaytseva et al. name phase change optical metamaterials and metasurfaces as attractive uses.
  watch_out:
    - Disagreeing values. Melting point is 632 °C in the globalsino table and about 610 °C in Zhang et al. The crystallization temperature is 151 to 174 °C in the table and about 175 °C in Zhang et al.
    - Several values are from thin films, and the sources do not always state the film form or thickness.
    - No radiation or space test of this alloy was read in this run, so radiation tolerance is not shown by these sources.
  verdict: Ge2Sb2Te5 is the reference phase-change alloy for two-state memory. The sources read here agree on its switching between resistive states, but they disagree on its transition temperatures. They give no alloy-level hazard or radiation data; the element-level GHS records are listed under risks.hazards.