Al–O phases

9 phases (tier A 3, tier C 1, liquid 2, gas 2, unresolved_no_candidates 1); 6 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 · Al–O system page · Markdown · field reference

Phases of the Al–O system (9)
Phase	Structure	Basis	Stability (calculated)	TDB models
BCC_A2 phase:al-o:bcc-a2	W · A2 · cI2 · Im-3m (229)	tier A: standard phase name	not stable in 3 calculated diagram(s)	3
CORUNDUM_D51 phase:al-o:d51-corundum	alpha-Al2O3 · D5_1 · hR10 · R-3c (167)	tier C: assessor-stated (Hallstedt 2025 crystallographic table)	stable in 3 of 3 calculated diagram(s): 300–2327 K, x(O) 0.6–0.6	3
DILUTE phase:al-o:dilute		unresolved_no_candidates	stable in 2 of 2 calculated diagram(s): 2054.81–2500 K, x(O) 0–0.00071	2
FCC_A1 phase:al-o:fcc-a1	Cu · A1 · cF4 · Fm-3m (225)	tier A: standard phase name	stable in 3 of 3 calculated diagram(s): 300–345 K, x(O) 0–0	3
GAS phase:al-o:gas	gas	gas	stable in 3 of 3 calculated diagram(s): 2213.75–2500 K, x(O) 0.30484–1	3
HCP_A3 phase:al-o:hcp-a3	Mg · A3 · hP2 · P6_3/mmc (194)	tier A: standard phase name	not stable in 3 calculated diagram(s)	3
ION phase:al-o:ion	liquid	liquid	stable in 3 of 3 calculated diagram(s): 2054.81–2500 K, x(O) 0–0.6	3
LIQUID phase:al-o:liquid	liquid	liquid	not stable in 3 calculated diagram(s)	3
O2GAS phase:al-o:o2gas	gas	gas	stable in 3 of 3 calculated diagram(s): 300–825 K, x(O) 1–1	3

BCC_A2 (Al–O)

Id: phase:al-o:bcc-a2; status assigned
Structure: W · A2 · cI2 · Im-3m (229); type st:a2-w-ci2; tier A: standard phase name; confidence high
Stoichiometry: Al 1.0000
Stability: not stable in 3 calculated diagram(s)
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (4): corpus: corpus:phase:al-o:bcc-a2
tdb: tdb:AlO-23Li.tdb:BCC_A2, tdb:AlO-92Tay.tdb:BCC_A2, tdb:AlO-93Hal-LB.tdb:BCC_A2

TDB models of BCC_A2 (3): PHASE and CONSTITUENT statements as written

AlO-23Li.tdb: BCC_A2, type code %B, sha256 b626da52ef13746e…

52: PHASE BCC_A2 %B 2 1 3 !
53: CONST BCC_A2 : AL : VA : !

AlO-92Tay.tdb: BCC_A2, type code %B, sha256 f56b31da71628e62…

53: PHASE BCC_A2 %B 2 1 3 !
54: CONST BCC_A2 : AL : VA : !

AlO-93Hal-LB.tdb: BCC_A2, type code %B, sha256 3893b53d655fc07c…

61: PHASE BCC_A2 %B 2 1 3 !
62: CONST BCC_A2 : AL : VA : !

Example references (3 of 3; assessments first):

doi:10.1007/BF02667878 B. Hallstedt, J. Phase Equilib., 14, 662-75(1993).
assessment that models this phase
doi:10.1016/0364-5916(92)90005-I J.R. Taylor, A.T. Dinsdale, M. Hillert, M. Selleby, Calphad, 16, 173-79(1992).
assessment that models this phase
doi:10.2298/JMMB230621034L X.-J. Li, S.-H. Liu, J. Mining Metall. B, 59, 395-405(2023).
assessment that models this phase

CORUNDUM_D51 (Al–O)

Id: phase:al-o:d51-corundum; status assigned
Structure: alpha-Al2O3 · D5_1 · hR10 · R-3c (167); type st:d5-1-alpha-al2o3-hr10; tier C: assessor-stated (Hallstedt 2025 crystallographic table); confidence assessor-stated
Structure source: B. Hallstedt, The SGTE collection of binary datasets, Calphad 89 (2025) 102833, supplementary crystallographic table (mmc2) doi:10.1016/j.calphad.2025.102833
Caveat: not certain from the name or DFT alone (unrecognised_name_tokens:CORUNDUM); structure as stated in the SGTE crystallographic table for this phase name and system
Stability: stable in 3 of 3 calculated diagram(s): 300–2327 K, x(O) 0.6–0.6
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (4): corpus: corpus:phase:al-o:d51-corundum
tdb: tdb:AlO-23Li.tdb:CORUNDUM_D51, tdb:AlO-92Tay.tdb:CORUNDUM_D51, tdb:AlO-93Hal-LB.tdb:CORUNDUM_D51

TDB models of CORUNDUM_D51 (3): PHASE and CONSTITUENT statements as written

AlO-23Li.tdb: CORUNDUM_D51, type code %A, sha256 b626da52ef13746e…

62: PHASE CORUNDUM_D51:I %A 2 2 3 !
63: CONST CORUNDUM_D51:I : AL+3 : O-2 : !

AlO-92Tay.tdb: CORUNDUM_D51, type code %A, sha256 f56b31da71628e62…

63: PHASE CORUNDUM_D51:I %A 2 2 3 !
64: CONST CORUNDUM_D51:I : AL+3 : O-2 : !

AlO-93Hal-LB.tdb: CORUNDUM_D51, type code %A, sha256 3893b53d655fc07c…

71: PHASE CORUNDUM_D51:I %A 2 2 3 !
72: CONST CORUNDUM_D51:I : AL+3 : O-2 : !

Example references (3 of 3; assessments first):

doi:10.1007/BF02667878 B. Hallstedt, J. Phase Equilib., 14, 662-75(1993).
assessment that models this phase
doi:10.1016/0364-5916(92)90005-I J.R. Taylor, A.T. Dinsdale, M. Hillert, M. Selleby, Calphad, 16, 173-79(1992).
assessment that models this phase
doi:10.2298/JMMB230621034L X.-J. Li, S.-H. Liu, J. Mining Metall. B, 59, 395-405(2023).
assessment that models this phase

DILUTE (Al–O)

Id: phase:al-o:dilute; status unresolved_no_candidates
No structure assigned. Why: name_has_descriptive_tokens:DILUTE; no_structure_token
Stability: stable in 2 of 2 calculated diagram(s): 2054.81–2500 K, x(O) 0–0.00071
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (3): corpus: corpus:phase:al-o:dilute
tdb: tdb:AlO-92Tay.tdb:DILUTE, tdb:AlO-93Hal-LB.tdb:DILUTE

TDB models of DILUTE (2): PHASE and CONSTITUENT statements as written

AlO-92Tay.tdb: DILUTE, type code %, sha256 f56b31da71628e62…

43: PHASE DILUTE % 1 1 !
44: CONST DILUTE : AL O : !

AlO-93Hal-LB.tdb: DILUTE, type code %, sha256 3893b53d655fc07c…

51: PHASE DILUTE % 1 1 !
52: CONST DILUTE : AL O : !

Example references (2 of 2; assessments first):

doi:10.1007/BF02667878 B. Hallstedt, J. Phase Equilib., 14, 662-75(1993).
assessment that models this phase
doi:10.1016/0364-5916(92)90005-I J.R. Taylor, A.T. Dinsdale, M. Hillert, M. Selleby, Calphad, 16, 173-79(1992).
assessment that models this phase

FCC_A1 (Al–O)

Id: phase:al-o:fcc-a1; status assigned
Structure: Cu · A1 · cF4 · Fm-3m (225); type st:a1-cu-cf4; tier A: standard phase name; confidence high
Stoichiometry: Al 1.0000
Stability: stable in 3 of 3 calculated diagram(s): 300–345 K, x(O) 0–0
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (4): corpus: corpus:phase:al-o:fcc-a1
tdb: tdb:AlO-23Li.tdb:FCC_A1, tdb:AlO-92Tay.tdb:FCC_A1, tdb:AlO-93Hal-LB.tdb:FCC_A1

TDB models of FCC_A1 (3): PHASE and CONSTITUENT statements as written

AlO-23Li.tdb: FCC_A1, type code %A, sha256 b626da52ef13746e…

47: PHASE FCC_A1 %A 2 1 1 !
48: CONST FCC_A1 : AL : VA : !

AlO-92Tay.tdb: FCC_A1, type code %A, sha256 f56b31da71628e62…

48: PHASE FCC_A1 %A 2 1 1 !
49: CONST FCC_A1 : AL : VA : !

AlO-93Hal-LB.tdb: FCC_A1, type code %A, sha256 3893b53d655fc07c…

56: PHASE FCC_A1 %A 2 1 1 !
57: CONST FCC_A1 : AL : VA : !

Example references (3 of 3; assessments first):

doi:10.1007/BF02667878 B. Hallstedt, J. Phase Equilib., 14, 662-75(1993).
assessment that models this phase
doi:10.1016/0364-5916(92)90005-I J.R. Taylor, A.T. Dinsdale, M. Hillert, M. Selleby, Calphad, 16, 173-79(1992).
assessment that models this phase
doi:10.2298/JMMB230621034L X.-J. Li, S.-H. Liu, J. Mining Metall. B, 59, 395-405(2023).
assessment that models this phase

GAS (Al–O)

Id: phase:al-o:gas; status assigned
Structure: gas; type st:gas; gas; confidence high
Stability: stable in 3 of 3 calculated diagram(s): 2213.75–2500 K, x(O) 0.30484–1
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (4): corpus: corpus:phase:al-o:gas
tdb: tdb:AlO-23Li.tdb:GAS, tdb:AlO-92Tay.tdb:GAS, tdb:AlO-93Hal-LB.tdb:GAS

TDB models of GAS (3): PHASE and CONSTITUENT statements as written

AlO-23Li.tdb: GAS, type code %, sha256 b626da52ef13746e…

65: PHASE GAS:G % 1 1 !
66: CONST GAS:G : AL% AL2 ALO ALO2 AL2O% AL2O2 AL2O3 O O2% O3 : !

AlO-92Tay.tdb: GAS, type code %, sha256 f56b31da71628e62…

66: PHASE GAS:G % 1 1 !
67: CONST GAS:G : AL% AL2 ALO ALO2 AL2O% AL2O2 AL2O3 O O2% O3 : !

AlO-93Hal-LB.tdb: GAS, type code %, sha256 3893b53d655fc07c…

74: PHASE GAS:G % 1 1 !
75: CONST GAS:G : AL% AL2 ALO ALO2 AL2O% AL2O2 AL2O3 O O2% O3 : !

Example references (3 of 3; assessments first):

doi:10.1007/BF02667878 B. Hallstedt, J. Phase Equilib., 14, 662-75(1993).
assessment that models this phase
doi:10.1016/0364-5916(92)90005-I J.R. Taylor, A.T. Dinsdale, M. Hillert, M. Selleby, Calphad, 16, 173-79(1992).
assessment that models this phase
doi:10.2298/JMMB230621034L X.-J. Li, S.-H. Liu, J. Mining Metall. B, 59, 395-405(2023).
assessment that models this phase

HCP_A3 (Al–O)

Id: phase:al-o:hcp-a3; status assigned
Structure: Mg · A3 · hP2 · P6_3/mmc (194); type st:a3-mg-hp2; tier A: standard phase name; confidence high
Stoichiometry: Al 1.0000
Stability: not stable in 3 calculated diagram(s)
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (4): corpus: corpus:phase:al-o:hcp-a3
tdb: tdb:AlO-23Li.tdb:HCP_A3, tdb:AlO-92Tay.tdb:HCP_A3, tdb:AlO-93Hal-LB.tdb:HCP_A3

TDB models of HCP_A3 (3): PHASE and CONSTITUENT statements as written

AlO-23Li.tdb: HCP_A3, type code %A, sha256 b626da52ef13746e…

57: PHASE HCP_A3 %A 2 1 0.5 !
58: CONST HCP_A3 : AL : VA : !

AlO-92Tay.tdb: HCP_A3, type code %A, sha256 f56b31da71628e62…

58: PHASE HCP_A3 %A 2 1 0.5 !
59: CONST HCP_A3 : AL : VA : !

AlO-93Hal-LB.tdb: HCP_A3, type code %A, sha256 3893b53d655fc07c…

66: PHASE HCP_A3 %A 2 1 0.5 !
67: CONST HCP_A3 : AL : VA : !

Example references (3 of 3; assessments first):

doi:10.1007/BF02667878 B. Hallstedt, J. Phase Equilib., 14, 662-75(1993).
assessment that models this phase
doi:10.1016/0364-5916(92)90005-I J.R. Taylor, A.T. Dinsdale, M. Hillert, M. Selleby, Calphad, 16, 173-79(1992).
assessment that models this phase
doi:10.2298/JMMB230621034L X.-J. Li, S.-H. Liu, J. Mining Metall. B, 59, 395-405(2023).
assessment that models this phase

ION (Al–O)

Id: phase:al-o:ion; status assigned
Structure: liquid; type st:liquid; liquid; confidence high
Stability: stable in 3 of 3 calculated diagram(s): 2054.81–2500 K, x(O) 0–0.6
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (4): corpus: corpus:phase:al-o:ion
tdb: tdb:AlO-23Li.tdb:ION, tdb:AlO-92Tay.tdb:ION, tdb:AlO-93Hal-LB.tdb:ION

TDB models of ION (3): PHASE and CONSTITUENT statements as written

AlO-23Li.tdb: ION, type code %, sha256 b626da52ef13746e…

39: PHASE ION:Y % 2 1 1 !
40: CONST ION:Y : AL+3 : O-2 VA : !

AlO-92Tay.tdb: ION, type code %, sha256 f56b31da71628e62…

37: PHASE ION:Y % 2 1 1 !
38: CONST ION:Y : AL+3 : O-2 VA : !

AlO-93Hal-LB.tdb: ION, type code %, sha256 3893b53d655fc07c…

45: PHASE ION:Y % 2 1 1 !
46: CONST ION:Y : AL+3 : O-2 VA ALO3/2% : !

Example references (3 of 3; assessments first):

doi:10.1007/BF02667878 B. Hallstedt, J. Phase Equilib., 14, 662-75(1993).
assessment that models this phase
doi:10.1016/0364-5916(92)90005-I J.R. Taylor, A.T. Dinsdale, M. Hillert, M. Selleby, Calphad, 16, 173-79(1992).
assessment that models this phase
doi:10.2298/JMMB230621034L X.-J. Li, S.-H. Liu, J. Mining Metall. B, 59, 395-405(2023).
assessment that models this phase

LIQUID (Al–O)

Id: phase:al-o:liquid; status assigned
Structure: liquid; type st:liquid; liquid; confidence high
Stability: not stable in 3 calculated diagram(s)
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (4): corpus: corpus:phase:al-o:liquid
tdb: tdb:AlO-23Li.tdb:LIQUID, tdb:AlO-92Tay.tdb:LIQUID, tdb:AlO-93Hal-LB.tdb:LIQUID

TDB models of LIQUID (3): PHASE and CONSTITUENT statements as written

AlO-23Li.tdb: LIQUID, type code %, sha256 b626da52ef13746e…

42: PHASE LIQUID:L % 1 1 !
43: CONST LIQUID:L : AL : !

AlO-92Tay.tdb: LIQUID, type code %, sha256 f56b31da71628e62…

40: PHASE LIQUID:L % 1 1 !
41: CONST LIQUID:L : AL ALO3/2 : !

AlO-93Hal-LB.tdb: LIQUID, type code %, sha256 3893b53d655fc07c…

48: PHASE LIQUID:L % 1 1 !
49: CONST LIQUID:L : AL ALO3/2 : !

Example references (3 of 3; assessments first):

doi:10.1007/BF02667878 B. Hallstedt, J. Phase Equilib., 14, 662-75(1993).
assessment that models this phase
doi:10.1016/0364-5916(92)90005-I J.R. Taylor, A.T. Dinsdale, M. Hillert, M. Selleby, Calphad, 16, 173-79(1992).
assessment that models this phase
doi:10.2298/JMMB230621034L X.-J. Li, S.-H. Liu, J. Mining Metall. B, 59, 395-405(2023).
assessment that models this phase

O2GAS (Al–O)

Id: phase:al-o:o2gas; status assigned
Structure: gas; type st:gas; gas; confidence high
Stability: stable in 3 of 3 calculated diagram(s): 300–825 K, x(O) 1–1
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (4): corpus: corpus:phase:al-o:o2gas
tdb: tdb:AlO-23Li.tdb:O2GAS, tdb:AlO-92Tay.tdb:O2GAS, tdb:AlO-93Hal-LB.tdb:O2GAS

TDB models of O2GAS (3): PHASE and CONSTITUENT statements as written

AlO-23Li.tdb: O2GAS, type code %, sha256 b626da52ef13746e…

68: PHASE O2GAS % 1 1 !
69: CONST O2GAS : O2 : !

AlO-92Tay.tdb: O2GAS, type code %, sha256 f56b31da71628e62…

69: PHASE O2GAS % 1 1 !
70: CONST O2GAS : O2 : !

AlO-93Hal-LB.tdb: O2GAS, type code %, sha256 3893b53d655fc07c…

77: PHASE O2GAS % 1 1 !
78: CONST O2GAS : O2 : !

Example references (3 of 3; assessments first):

doi:10.1007/BF02667878 B. Hallstedt, J. Phase Equilib., 14, 662-75(1993).
assessment that models this phase
doi:10.1016/0364-5916(92)90005-I J.R. Taylor, A.T. Dinsdale, M. Hillert, M. Selleby, Calphad, 16, 173-79(1992).
assessment that models this phase
doi:10.2298/JMMB230621034L X.-J. Li, S.-H. Liu, J. Mining Metall. B, 59, 395-405(2023).
assessment that models this phase

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}
}