H–O phases

4 phases (liquid 1, gas 3); 2 stable in a calculated diagram. Structure types are assigned only when the stored evidence supports an assignment under the stated tier rules (tier A: standard phase name; tier B: unique Materials Project + OQMD on-hull match, DFT-supported; tier C: one structure stated by the assessment's crystallographic table, assessor-stated); other phases list candidates and are marked needs_review. Stability is from phase diagrams calculated with pycalphad from the SGTE binary collection (evidence class: model).

Data: interactive registry · full JSON · H–O system page · Markdown · field reference

Phases of the H–O system (4)
Phase	Structure	Basis	Stability (calculated)	TDB models
GAS phase:h-o:gas	gas	gas	stable in 1 of 1 calculated diagram(s): 300–2500 K, x(O) 0–1	1
H2GAS phase:h-o:h2gas	gas	gas	not stable in 1 calculated diagram(s)	1
LIQUID phase:h-o:liquid	liquid	liquid	stable in 1 of 1 calculated diagram(s): 300–373.44 K, x(O) 0.33333–0.33333	1
O2GAS phase:h-o:o2gas	gas	gas	not stable in 1 calculated diagram(s)	1

GAS (H–O)

Id: phase:h-o:gas; status assigned
Structure: gas; type st:gas; gas; confidence high
Stability: stable in 1 of 1 calculated diagram(s): 300–2500 K, x(O) 0–1
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (2): corpus: corpus:phase:h-o:gas
tdb: tdb:HO-97SUB.tdb:GAS

TDB models of GAS (1): PHASE and CONSTITUENT statements as written

HO-97SUB.tdb: GAS, type code %, sha256 b481d8010be99a89…

32: PHASE GAS:G % 1 1 !
33: CONST GAS:G : H H2 H1O1 H1O2 H2O H2O2 O O2% O3 : !

H2GAS (H–O)

Id: phase:h-o:h2gas; status assigned
Structure: gas; type st:gas; gas; confidence high
Stability: not stable in 1 calculated diagram(s)
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (2): corpus: corpus:phase:h-o:h2gas
tdb: tdb:HO-97SUB.tdb:H2GAS

TDB models of H2GAS (1): PHASE and CONSTITUENT statements as written

HO-97SUB.tdb: H2GAS, type code %, sha256 b481d8010be99a89…

35: PHASE H2GAS % 1 1 !
36: CONST H2GAS : H2 : !

LIQUID (H–O)

Id: phase:h-o:liquid; status assigned
Structure: liquid; type st:liquid; liquid; confidence high
Stability: stable in 1 of 1 calculated diagram(s): 300–373.44 K, x(O) 0.33333–0.33333
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (2): corpus: corpus:phase:h-o:liquid
tdb: tdb:HO-97SUB.tdb:LIQUID

TDB models of LIQUID (1): PHASE and CONSTITUENT statements as written

HO-97SUB.tdb: LIQUID, type code %, sha256 b481d8010be99a89…

29: PHASE LIQUID:L % 1 1 !
30: CONST LIQUID:L : H2O : !

O2GAS (H–O)

Id: phase:h-o:o2gas; status assigned
Structure: gas; type st:gas; gas; confidence high
Stability: not stable in 1 calculated diagram(s)
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (2): corpus: corpus:phase:h-o:o2gas
tdb: tdb:HO-97SUB.tdb:O2GAS

TDB models of O2GAS (1): PHASE and CONSTITUENT statements as written

HO-97SUB.tdb: O2GAS, type code %, sha256 b481d8010be99a89…

38: PHASE O2GAS % 1 1 !
39: CONST O2GAS : O2 : !

Please cite

R. Arróyave, J. Saal, D. Shin, ORCHID-Registry: phase registry of binary systems (version 2026.10; Version 1, machine-extracted), Zenodo (2026). doi:10.5281/zenodo.23735970
R. Arróyave, J. Saal, D. Shin, ORCHID data: umbrella record of the ORCHID datasets (version 2026.10; Version 1, machine-extracted), Zenodo (2026). doi:10.5281/zenodo.23736065

Also cite B. Hallstedt, The SGTE collection of binary datasets, Calphad 89 (2025) 102833, https://doi.org/10.1016/j.calphad.2025.102833 (CC BY 4.0), and the original assessment named in each file; A. Jain et al., The Materials Project: A materials genome approach to accelerating materials innovation, APL Materials 1 (2013) 011002, https://doi.org/10.1063/1.4812323 (CC BY 4.0); J. E. Saal et al., JOM 65 (2013) 1501, https://doi.org/10.1007/s11837-013-0755-4 and S. Kirklin et al., npj Comput. Mater. 1 (2015) 15010, https://doi.org/10.1038/npjcompumats.2015.10 (CC BY 4.0); the original source of every value you use (paper_citation / paper_doi, and cited_dois for values the paper cites from earlier work). Version 1, machine-extracted: values were read by language-model readers constrained to quote their source and checked automatically, and the release was then audited on the printed pages by adversarial audits, an independent second review of fit-facing records and a preliminary human review of a frozen sample. Flags such as accepted and ESPEI-ready record screening results, not certification; known issues are listed in the release notes.

@misc{orchid_phase_registry_2026,
  author    = {Arr{\'o}yave, Raymundo and Saal, James and Shin, Dongwon},
  title     = {{ORCHID-Registry: phase registry of binary systems}},
  version   = {2026.10},
  publisher = {Zenodo},
  year      = {2026},
  doi       = {10.5281/zenodo.23735970},
  url       = {https://doi.org/10.5281/zenodo.23735970},
  note      = {Version 1, machine-extracted}
}

@misc{orchid_data_2026,
  author    = {Arr{\'o}yave, Raymundo and Saal, James and Shin, Dongwon},
  title     = {{ORCHID data: umbrella record of the ORCHID datasets}},
  version   = {2026.10},
  publisher = {Zenodo},
  year      = {2026},
  doi       = {10.5281/zenodo.23736065},
  url       = {https://doi.org/10.5281/zenodo.23736065},
  note      = {Version 1, machine-extracted}
}