Na–O phases

12 phases (tier A 5, liquid 1, gas 2, needs_review 4); 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 · Na–O system page · Markdown · field reference

Phases of the Na–O system (12)
Phase	Structure	Basis	Stability (calculated)	Literature values	TDB models
BCC_A2 phase:na-o:bcc-a2	W · A2 · cI2 · Im-3m (229)	tier A: standard phase name	stable in 1 of 1 calculated diagram(s): 300–301 K, x(O) 0–0	4	1
FCC_A1 phase:na-o:fcc-a1	Cu · A1 · cF4 · Fm-3m (225)	tier A: standard phase name	not stable in 1 calculated diagram(s)	0	1
GAS phase:na-o:gas	gas	gas	stable in 1 of 1 calculated diagram(s): 1006.07–2111.07 K, x(O) 0.39956–1	0	1
HCP_A3 phase:na-o:hcp-a3	Mg · A3 · hP2 · P6_3/mmc (194)	tier A: standard phase name	not stable in 1 calculated diagram(s)	0	1
ION phase:na-o:ion	liquid	liquid	stable in 1 of 1 calculated diagram(s): 1006.07–2111.07 K, x(O) 0.3426–0.49063	0	1
NA2O_C1 phase:na-o:na2o-c1	CaF2 · C1 · cF12 · Fm-3m (225)	tier A: standard phase name	stable in 1 of 1 calculated diagram(s): 300–301 K, x(O) 0.33333–0.33333	7	1
NA2O_II phase:na-o:na2o-ii		needs_review	not stable in 1 calculated diagram(s)	4	1
NA2O_III phase:na-o:na2o-iii		needs_review	not stable in 1 calculated diagram(s)	6	1
NA2O2_I phase:na-o:na2o2-i		needs_review	stable in 1 of 1 calculated diagram(s): 300–422.5 K, x(O) 0.5–0.5	4	1
NA2O2_II phase:na-o:na2o2-ii		needs_review	not stable in 1 calculated diagram(s)	5	1
NAO2_B1 phase:na-o:nao2-b1	NaCl · B1 · cF8 · Fm-3m (225)	tier A: standard phase name	not stable in 1 calculated diagram(s)	0	1
O2GAS phase:na-o:o2gas	gas	gas	stable in 1 of 1 calculated diagram(s): 300–422.5 K, x(O) 1–1	0	1

BCC_A2 (Na–O)

Id: phase:na-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: Na 1.0000
Stability: stable in 1 of 1 calculated diagram(s): 300–301 K, x(O) 0–0
Literature: 4 values (4 accepted) from 1 papers
Interactive: phase registry entry

Names (3): corpus: corpus:phase:na-o:bcc-a2
paper: paper:10.1016/j.jct.2017.04.003:β-Na
tdb: tdb:NaO-17Smi.tdb:BCC_A2

TDB models of BCC_A2 (1): PHASE and CONSTITUENT statements as written

NaO-17Smi.tdb: BCC_A2, type code %B, sha256 4ebf441b547a4b28…

47: PHASE BCC_A2 %B 2 1 3 !
48: CONST BCC_A2 : NA : VA : !

Example references (2 of 2; assessments first):

doi:10.1016/j.jct.2017.04.003 A.L. Smith, C. Guéneau, J.-L. Flèche, S. Chatain, O. Beneš, R.J.M. Konings, Thermodynamic assessment of the Na-O and Na-U-O systems: Margin to the safe operation of SFRs, The Journal of Chemical Thermodynamics 114, 93-115 (2017).
assessment that models this phase; reports values for this phase
doi:10.1007/bf02874915 H. A. Wriedt, The Na−O (Sodium-Oxygen) System, Bulletin of Alloy Phase Diagrams 8, 234-246 (1987).
cited as the source of values for this phase

FCC_A1 (Na–O)

Id: phase:na-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: Na 1.0000
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:na-o:fcc-a1
tdb: tdb:NaO-17Smi.tdb:FCC_A1

TDB models of FCC_A1 (1): PHASE and CONSTITUENT statements as written

NaO-17Smi.tdb: FCC_A1, type code %A, sha256 4ebf441b547a4b28…

42: PHASE FCC_A1 %A 2 1 1 !
43: CONST FCC_A1 : NA : VA : !

Example references (1 of 1; assessments first):

doi:10.1016/j.jct.2017.04.003 A.L. Smith, C. Guéneau, J.-L. Flèche, S. Chatain, O. Beneš, R.J.M. Konings, Thermodynamic assessment of the Na-O and Na-U-O systems: Margin to the safe operation of SFRs, The Journal of Chemical Thermodynamics 114, 93-115 (2017).
assessment that models this phase

GAS (Na–O)

Id: phase:na-o:gas; status assigned
Structure: gas; type st:gas; gas; confidence high
Stability: stable in 1 of 1 calculated diagram(s): 1006.07–2111.07 K, x(O) 0.39956–1
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (2): corpus: corpus:phase:na-o:gas
tdb: tdb:NaO-17Smi.tdb:GAS

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

NaO-17Smi.tdb: GAS, type code %, sha256 4ebf441b547a4b28…

88: PHASE GAS:G % 1 1 !
89: CONST GAS:G : NA NA2 NA2O NA2O2 O O2 O3 : !

Example references (1 of 1; assessments first):

doi:10.1016/j.jct.2017.04.003 A.L. Smith, C. Guéneau, J.-L. Flèche, S. Chatain, O. Beneš, R.J.M. Konings, Thermodynamic assessment of the Na-O and Na-U-O systems: Margin to the safe operation of SFRs, The Journal of Chemical Thermodynamics 114, 93-115 (2017).
assessment that models this phase

HCP_A3 (Na–O)

Id: phase:na-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: Na 1.0000
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:na-o:hcp-a3
tdb: tdb:NaO-17Smi.tdb:HCP_A3

TDB models of HCP_A3 (1): PHASE and CONSTITUENT statements as written

NaO-17Smi.tdb: HCP_A3, type code %A, sha256 4ebf441b547a4b28…

52: PHASE HCP_A3 %A 2 1 0.5 !
53: CONST HCP_A3 : NA : VA : !

Example references (1 of 1; assessments first):

doi:10.1016/j.jct.2017.04.003 A.L. Smith, C. Guéneau, J.-L. Flèche, S. Chatain, O. Beneš, R.J.M. Konings, Thermodynamic assessment of the Na-O and Na-U-O systems: Margin to the safe operation of SFRs, The Journal of Chemical Thermodynamics 114, 93-115 (2017).
assessment that models this phase

ION (Na–O)

Id: phase:na-o:ion; status assigned
Structure: liquid; type st:liquid; liquid; confidence high
Stability: stable in 1 of 1 calculated diagram(s): 1006.07–2111.07 K, x(O) 0.3426–0.49063
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (2): corpus: corpus:phase:na-o:ion
tdb: tdb:NaO-17Smi.tdb:ION

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

NaO-17Smi.tdb: ION, type code %, sha256 4ebf441b547a4b28…

37: PHASE ION:Y % 2 1 1 !
38: CONST ION:Y : NA+1 : O-2 VA NA2O2 O : !

Example references (1 of 1; assessments first):

doi:10.1016/j.jct.2017.04.003 A.L. Smith, C. Guéneau, J.-L. Flèche, S. Chatain, O. Beneš, R.J.M. Konings, Thermodynamic assessment of the Na-O and Na-U-O systems: Margin to the safe operation of SFRs, The Journal of Chemical Thermodynamics 114, 93-115 (2017).
assessment that models this phase

NA2O_C1 (Na–O)

Id: phase:na-o:na2o-c1; status assigned
Structure: CaF2 · C1 · cF12 · Fm-3m (225); type st:c1-caf2-cf12; tier A: standard phase name; confidence high
Stability: stable in 1 of 1 calculated diagram(s): 300–301 K, x(O) 0.33333–0.33333
Literature: 7 values (6 accepted) from 1 papers
Interactive: phase registry entry

Names (4): corpus: corpus:phase:na-o:na2o-c1
paper: paper:10.1016/j.jct.2017.04.003:Na2O-I, paper:10.1016/j.jct.2017.04.003:Na2O-I(cr)
tdb: tdb:NaO-17Smi.tdb:NA2O_C1

TDB models of NA2O_C1 (1): PHASE and CONSTITUENT statements as written

NaO-17Smi.tdb: NA2O_C1, type code %, sha256 4ebf441b547a4b28…

57: PHASE NA2O_C1 % 2 2 1 !
58: CONST NA2O_C1 : NA+1 : O-2 : !

Example references (2 of 2; assessments first):

doi:10.1016/j.jct.2017.04.003 A.L. Smith, C. Guéneau, J.-L. Flèche, S. Chatain, O. Beneš, R.J.M. Konings, Thermodynamic assessment of the Na-O and Na-U-O systems: Margin to the safe operation of SFRs, The Journal of Chemical Thermodynamics 114, 93-115 (2017).
assessment that models this phase; reports values for this phase
doi:10.1007/bf02874915 H. A. Wriedt, The Na−O (Sodium-Oxygen) System, Bulletin of Alloy Phase Diagrams 8, 234-246 (1987).
cited as the source of values for this phase

NA2O_II (Na–O)

Id: phase:na-o:na2o-ii; status needs_review
No structure assigned. Why: name_has_descriptive_tokens:II; no_structure_token
Candidate (sgte_mmc2): (Na2O-II) — Hallstedt 2025 mmc2 row for NA2O_II: Na2O-II
Stability: not stable in 1 calculated diagram(s)
Literature: 4 values (4 accepted) from 1 papers
Interactive: phase registry entry

Names (3): corpus: corpus:phase:na-o:na2o-ii
paper: paper:10.1016/j.jct.2017.04.003:Na2O-II
tdb: tdb:NaO-17Smi.tdb:NA2O_II

TDB models of NA2O_II (1): PHASE and CONSTITUENT statements as written

NaO-17Smi.tdb: NA2O_II, type code %, sha256 4ebf441b547a4b28…

62: PHASE NA2O_II % 2 2 1 !
63: CONST NA2O_II : NA+1 : O-2 : !

Example references (1 of 1; assessments first):

doi:10.1016/j.jct.2017.04.003 A.L. Smith, C. Guéneau, J.-L. Flèche, S. Chatain, O. Beneš, R.J.M. Konings, Thermodynamic assessment of the Na-O and Na-U-O systems: Margin to the safe operation of SFRs, The Journal of Chemical Thermodynamics 114, 93-115 (2017).
assessment that models this phase; reports values for this phase

NA2O_III (Na–O)

Id: phase:na-o:na2o-iii; status needs_review
No structure assigned. Why: name_has_descriptive_tokens:III; no_structure_token
Candidate (sgte_mmc2): (Na2O-III) — Hallstedt 2025 mmc2 row for NA2O_III: Na2O-III
Stability: not stable in 1 calculated diagram(s)
Literature: 6 values (6 accepted) from 1 papers
Interactive: phase registry entry

Names (3): corpus: corpus:phase:na-o:na2o-iii
paper: paper:10.1016/j.jct.2017.04.003:Na2O-III
tdb: tdb:NaO-17Smi.tdb:NA2O_III

TDB models of NA2O_III (1): PHASE and CONSTITUENT statements as written

NaO-17Smi.tdb: NA2O_III, type code %, sha256 4ebf441b547a4b28…

67: PHASE NA2O_III % 2 2 1 !
68: CONST NA2O_III : NA+1 : O-2 : !

Example references (2 of 2; assessments first):

doi:10.1016/j.jct.2017.04.003 A.L. Smith, C. Guéneau, J.-L. Flèche, S. Chatain, O. Beneš, R.J.M. Konings, Thermodynamic assessment of the Na-O and Na-U-O systems: Margin to the safe operation of SFRs, The Journal of Chemical Thermodynamics 114, 93-115 (2017).
assessment that models this phase; reports values for this phase
doi:10.1007/bf02874915 H. A. Wriedt, The Na−O (Sodium-Oxygen) System, Bulletin of Alloy Phase Diagrams 8, 234-246 (1987).
cited as the source of values for this phase

NA2O2_I (Na–O)

Id: phase:na-o:na2o2-i; status needs_review
No structure assigned. Why: name_has_descriptive_tokens:I; no_structure_token
Candidate (dft_mp): P-62m (189) — on-hull MP Na2O2 at x(O)=0.5000
Candidate (dft_oqmd): P-62m (189) — on-hull OQMD Na1 O1 at x(O)=0.5000
Candidate (sgte_mmc2): Na2O2 · hP12 · P-62m (189) — Hallstedt 2025 mmc2 row for NA2O2_I: Na2O2-I
Candidate (tdb_comment): Na2O2 · hP12 · P-62m — NaO-17Smi.tdb: 'Prototype Na2O2 (hP12, P-62m)'
Stability: stable in 1 of 1 calculated diagram(s): 300–422.5 K, x(O) 0.5–0.5
Literature: 4 values (4 accepted) from 1 papers
Interactive: phase registry entry

Names (4): corpus: corpus:phase:na-o:na2o2-i
paper: paper:10.1016/j.jct.2017.04.003:Na2O2-I, paper:10.1016/j.jct.2017.04.003:Na2O2-I(cr)
tdb: tdb:NaO-17Smi.tdb:NA2O2_I

TDB models of NA2O2_I (1): PHASE and CONSTITUENT statements as written

NaO-17Smi.tdb: NA2O2_I, type code %, sha256 4ebf441b547a4b28…

72: PHASE NA2O2_I % 2 2 1 !
73: CONST NA2O2_I : NA+1 : O2-2 : !

Example references (1 of 1; assessments first):

doi:10.1016/j.jct.2017.04.003 A.L. Smith, C. Guéneau, J.-L. Flèche, S. Chatain, O. Beneš, R.J.M. Konings, Thermodynamic assessment of the Na-O and Na-U-O systems: Margin to the safe operation of SFRs, The Journal of Chemical Thermodynamics 114, 93-115 (2017).
assessment that models this phase; reports values for this phase

NA2O2_II (Na–O)

Id: phase:na-o:na2o2-ii; status needs_review
No structure assigned. Why: name_has_descriptive_tokens:II; no_structure_token
Candidate (sgte_mmc2): (Na2O2-II) — Hallstedt 2025 mmc2 row for NA2O2_II: Na2O2-II
Stability: not stable in 1 calculated diagram(s)
Literature: 5 values (5 accepted) from 1 papers
Interactive: phase registry entry

Names (3): corpus: corpus:phase:na-o:na2o2-ii
paper: paper:10.1016/j.jct.2017.04.003:Na2O2-II
tdb: tdb:NaO-17Smi.tdb:NA2O2_II

TDB models of NA2O2_II (1): PHASE and CONSTITUENT statements as written

NaO-17Smi.tdb: NA2O2_II, type code %, sha256 4ebf441b547a4b28…

77: PHASE NA2O2_II % 2 2 1 !
78: CONST NA2O2_II : NA+1 : O2-2 : !

Example references (1 of 1; assessments first):

doi:10.1016/j.jct.2017.04.003 A.L. Smith, C. Guéneau, J.-L. Flèche, S. Chatain, O. Beneš, R.J.M. Konings, Thermodynamic assessment of the Na-O and Na-U-O systems: Margin to the safe operation of SFRs, The Journal of Chemical Thermodynamics 114, 93-115 (2017).
assessment that models this phase; reports values for this phase

NAO2_B1 (Na–O)

Id: phase:na-o:nao2-b1; status assigned
Structure: NaCl · B1 · cF8 · Fm-3m (225); type st:b1-nacl-cf8; tier A: standard phase name; 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:na-o:nao2-b1
tdb: tdb:NaO-17Smi.tdb:NAO2_B1

TDB models of NAO2_B1 (1): PHASE and CONSTITUENT statements as written

NaO-17Smi.tdb: NAO2_B1, type code %, sha256 4ebf441b547a4b28…

82: PHASE NAO2_B1 % 1 1 !
83: CONST NAO2_B1 : NAO2 : !

Example references (1 of 1; assessments first):

doi:10.1016/j.jct.2017.04.003 A.L. Smith, C. Guéneau, J.-L. Flèche, S. Chatain, O. Beneš, R.J.M. Konings, Thermodynamic assessment of the Na-O and Na-U-O systems: Margin to the safe operation of SFRs, The Journal of Chemical Thermodynamics 114, 93-115 (2017).
assessment that models this phase

O2GAS (Na–O)

Id: phase:na-o:o2gas; status assigned
Structure: gas; type st:gas; gas; confidence high
Stability: stable in 1 of 1 calculated diagram(s): 300–422.5 K, x(O) 1–1
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (2): corpus: corpus:phase:na-o:o2gas
tdb: tdb:NaO-17Smi.tdb:O2GAS

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

NaO-17Smi.tdb: O2GAS, type code %, sha256 4ebf441b547a4b28…

85: PHASE O2GAS % 1 1 !
86: CONST O2GAS : O2 :!

Example references (1 of 1; assessments first):

doi:10.1016/j.jct.2017.04.003 A.L. Smith, C. Guéneau, J.-L. Flèche, S. Chatain, O. Beneš, R.J.M. Konings, Thermodynamic assessment of the Na-O and Na-U-O systems: Margin to the safe operation of SFRs, The Journal of Chemical Thermodynamics 114, 93-115 (2017).
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}
}