Ba–O phases

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

Phases of the Ba–O system (10)
Phase	Structure	Basis	Stability (calculated)	Literature values	TDB models
BAO phase:ba-o:bao		needs_review	stable in 1 of 1 calculated diagram(s): 300–2285.72 K, x(O) 0.5–0.66667	43	3
BAO_B1 phase:ba-o:bao-b1	NaCl · B1 · cF8 · Fm-3m (225)	tier A: standard phase name	no calculated diagram	0	2
BAO2_C11A phase:ba-o:bao2-c11a		needs_review	no calculated diagram	0	2
BCC_A2 phase:ba-o:bcc-a2	W · A2 · cI2 · Im-3m (229)	tier A: standard phase name	stable in 1 of 1 calculated diagram(s): 300–1041.25 K, x(O) 0–0	0	3
FCC_A1 phase:ba-o:fcc-a1	Cu · A1 · cF4 · Fm-3m (225)	tier A: standard phase name	not stable in 1 calculated diagram(s)	0	3
GAS phase:ba-o:gas	gas	gas	stable in 1 of 1 calculated diagram(s): 301.02–2500 K, x(O) 0–1	4	3
HCP_A3 phase:ba-o:hcp-a3	Mg · A3 · hP2 · P6_3/mmc (194)	tier A: standard phase name	not stable in 1 calculated diagram(s)	0	3
ION phase:ba-o:ion	liquid	liquid	no calculated diagram	0	2
LIQUID phase:ba-o:liquid	liquid	liquid	stable in 1 of 1 calculated diagram(s): 854.47–2500 K, x(O) 0–0.56843	6	1
O2GAS phase:ba-o:o2gas	gas	gas	stable in 1 of 1 calculated diagram(s): 300–1181.02 K, x(O) 1–1	0	3

BAO (Ba–O)

Id: phase:ba-o:bao; status needs_review
No structure assigned. Why: no_structure_token; off_stoichiometric_model; sgte_mmc2_rows_disagree
Candidate (dft_mp): Fm-3m (225) — on-hull MP BaO at x(O)=0.5000
Candidate (dft_mp): I4/mmm (139) — on-hull MP BaO2 at x(O)=0.6667
Candidate (dft_oqmd): R3 (146) — on-hull OQMD Ba1 O1 at x(O)=0.5000
Candidate (dft_oqmd): C2/m (12) — on-hull OQMD Ba1 O2 at x(O)=0.6667
Candidate (sgte_mmc2): NaCl · B1 · cF8 · Fm-3m (225) — Hallstedt 2025 mmc2 row for BAO: BaO (common model for BaO and BaO2)
Candidate (sgte_mmc2): CaC2 · C11_a · tI6 · I4/mmm (139) — Hallstedt 2025 mmc2 row for BAO: BaO2 (common model for BaO and BaO2)
Candidate (tdb_comment): CaC2 · tI6 · I4/mmm — BaO-05Zho-mod.tdb: 'Prototype CaC2 (tI6, I4/mmm), C11_a, barium peroxide'
Candidate (tdb_comment): NaCl · cF8 · Fm-3m — BaO-05Zho-mod.tdb: 'Prototype NaCl (cF8, Fm-3m), B1, barium oxide'
Stability: stable in 1 of 1 calculated diagram(s): 300–2285.72 K, x(O) 0.5–0.66667
Literature: 43 values (17 accepted) from 2 papers
Interactive: phase registry entry

Names (9): corpus: corpus:phase:ba-o:bao
paper: paper:10.1016/0364-5916(95)00012-4:BaO(G), paper:10.1016/0364-5916(95)00012-4:BaO(L), paper:10.1016/0364-5916(95)00012-4:BaO(S), paper:10.1016/0364-5916(95)00012-4:BaO2(S), paper:10.1111/j.1551-2916.2005.00368.x:BaO
tdb: tdb:BaO-05Zho-mod.tdb:BAO, tdb:BaO-05Zho.tdb:BAO, tdb:BaO-95Zim.tdb:BAO

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

BaO-05Zho-mod.tdb: BAO, type code %, sha256 1166f495f723a413…

76: PHASE BAO:I % 2 1 1 !
77: CONST BAO:I : BA+2 : O-2 O2-2 : !

BaO-05Zho.tdb: BAO, type code %, sha256 c272fdb1966d275b…

62: PHASE BAO:I % 2 1 1 !
63: CONST BAO:I : BA+2 : O-2 O2-2 : !

BaO-95Zim.tdb: BAO, type code %, sha256 a0f7658f38a4a7d7…

51: PHASE BAO % 1 1 !
52: CONST BAO : BAO BAO2 : !

Example references (2 of 2; assessments first):

doi:10.1016/0364-5916(95)00012-4 E. Zimmermann, K. Hack, D. Neuschütz, Thermochemical assessment of the binary system Ba-O, Calphad 19, 119-127 (1995).
assessment that models this phase; reports values for this phase
doi:10.1111/j.1551-2916.2005.00368.x Shihuai Zhou, Raymundo Arroyave, Clive A. Randall, Zi‐Kui Liu, Thermodynamic Modeling of the Binary Barium–Oxygen System, Journal of the American Ceramic Society 88, 1943-1948 (2005).
assessment that models this phase; reports values for this phase

BAO_B1 (Ba–O)

Id: phase:ba-o:bao-b1; status assigned
Structure: NaCl · B1 · cF8 · Fm-3m (225); type st:b1-nacl-cf8; tier A: standard phase name; confidence high
Stability: no calculated diagram
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (3): corpus: corpus:phase:ba-o:bao-b1
tdb: tdb:BaO-05Zho-mod.tdb:BAO_B1, tdb:BaO-05Zho.tdb:BAO_B1

TDB models of BAO_B1 (2): PHASE and CONSTITUENT statements as written

BaO-05Zho-mod.tdb: BAO_B1, type code %, sha256 1166f495f723a413…

81: PHASE BAO_B1:I % 2 1 1 !
82: CONST BAO_B1:I : BA+2 : O-2 O2-2 : !

BaO-05Zho.tdb: BAO_B1, type code %, sha256 c272fdb1966d275b…

67: PHASE BAO_B1:I % 2 1 1 !
68: CONST BAO_B1:I : BA+2 : O-2 O2-2 : !

Example references (1 of 1; assessments first):

doi:10.1111/j.1551-2916.2005.00368.x Shihuai Zhou, Raymundo Arroyave, Clive A. Randall, Zi‐Kui Liu, Thermodynamic Modeling of the Binary Barium–Oxygen System, Journal of the American Ceramic Society 88, 1943-1948 (2005).
assessment that models this phase

BAO2_C11A (Ba–O)

Id: phase:ba-o:bao2-c11a; status needs_review
No structure assigned. Why: assessment_declared_blocked_by:site_ratios_contradict_C11_a; site_ratios_contradict_C11_a:BaO-05Zho-mod.tdb; site_ratios_contradict_C11_a:BaO-05Zho.tdb
Candidate (name_token): CaC2 · C11_a · tI6 · I4/mmm (139) — Strukturbericht/word 'C11A' in the TDB name
Candidate (sgte_mmc2): CaC2 · C11_a · tI6 · I4/mmm (139) — Hallstedt 2025 mmc2 row for BAO2_C11A: BaO2
Candidate (tdb_comment): CaC2 · tI6 · I4/mmm — BaO-05Zho-mod.tdb: 'Prototype CaC2 (tI6, I4/mmm), C11_a, barium peroxide'
Candidate (tdb_comment): CaC2 · tI6 · I4/mmm — BaO-05Zho.tdb: 'Prototype CaC2 (tI6, I4/mmm), C11_a, barium peroxide'
Stability: no calculated diagram
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (3): corpus: corpus:phase:ba-o:bao2-c11a
tdb: tdb:BaO-05Zho-mod.tdb:BAO2_C11A, tdb:BaO-05Zho.tdb:BAO2_C11A

TDB models of BAO2_C11A (2): PHASE and CONSTITUENT statements as written

BaO-05Zho-mod.tdb: BAO2_C11A, type code %, sha256 1166f495f723a413…

86: PHASE BAO2_C11A:I % 2 1 1 !
87: CONST BAO2_C11A:I : BA+2 : O-2 O2-2 : !

BaO-05Zho.tdb: BAO2_C11A, type code %, sha256 c272fdb1966d275b…

72: PHASE BAO2_C11A:I % 2 1 1 !
73: CONST BAO2_C11A:I : BA+2 : O-2 O2-2 : !

Example references (1 of 1; assessments first):

doi:10.1111/j.1551-2916.2005.00368.x Shihuai Zhou, Raymundo Arroyave, Clive A. Randall, Zi‐Kui Liu, Thermodynamic Modeling of the Binary Barium–Oxygen System, Journal of the American Ceramic Society 88, 1943-1948 (2005).
assessment that models this phase

BCC_A2 (Ba–O)

Id: phase:ba-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: Ba 1.0000
Stability: stable in 1 of 1 calculated diagram(s): 300–1041.25 K, x(O) 0–0
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (4): corpus: corpus:phase:ba-o:bcc-a2
tdb: tdb:BaO-05Zho-mod.tdb:BCC_A2, tdb:BaO-05Zho.tdb:BCC_A2, tdb:BaO-95Zim.tdb:BCC_A2

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

BaO-05Zho-mod.tdb: BCC_A2, type code %B, sha256 1166f495f723a413…

65: PHASE BCC_A2 %B 2 1 3 !
66: CONST BCC_A2 : BA : VA : !

BaO-05Zho.tdb: BCC_A2, type code %B, sha256 c272fdb1966d275b…

51: PHASE BCC_A2 %B 2 1 3 !
52: CONST BCC_A2 : BA : VA : !

BaO-95Zim.tdb: BCC_A2, type code %B, sha256 a0f7658f38a4a7d7…

40: PHASE BCC_A2 %B 2 1 3 !
41: CONST BCC_A2 : BA : VA : !

Example references (2 of 2; assessments first):

doi:10.1016/0364-5916(95)00012-4 E. Zimmermann, K. Hack, D. Neuschütz, Thermochemical assessment of the binary system Ba-O, Calphad 19, 119-127 (1995).
assessment that models this phase
doi:10.1111/j.1551-2916.2005.00368.x Shihuai Zhou, Raymundo Arroyave, Clive A. Randall, Zi‐Kui Liu, Thermodynamic Modeling of the Binary Barium–Oxygen System, Journal of the American Ceramic Society 88, 1943-1948 (2005).
assessment that models this phase

FCC_A1 (Ba–O)

Id: phase:ba-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: Ba 1.0000
Stability: not stable in 1 calculated diagram(s)
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (4): corpus: corpus:phase:ba-o:fcc-a1
tdb: tdb:BaO-05Zho-mod.tdb:FCC_A1, tdb:BaO-05Zho.tdb:FCC_A1, tdb:BaO-95Zim.tdb:FCC_A1

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

BaO-05Zho-mod.tdb: FCC_A1, type code %A, sha256 1166f495f723a413…

60: PHASE FCC_A1 %A 2 1 1 !
61: CONST FCC_A1 : BA : VA : !

BaO-05Zho.tdb: FCC_A1, type code %A, sha256 c272fdb1966d275b…

46: PHASE FCC_A1 %A 2 1 1 !
47: CONST FCC_A1 : BA : VA : !

BaO-95Zim.tdb: FCC_A1, type code %A, sha256 a0f7658f38a4a7d7…

35: PHASE FCC_A1 %A 2 1 1 !
36: CONST FCC_A1 : BA : VA : !

Example references (2 of 2; assessments first):

doi:10.1016/0364-5916(95)00012-4 E. Zimmermann, K. Hack, D. Neuschütz, Thermochemical assessment of the binary system Ba-O, Calphad 19, 119-127 (1995).
assessment that models this phase
doi:10.1111/j.1551-2916.2005.00368.x Shihuai Zhou, Raymundo Arroyave, Clive A. Randall, Zi‐Kui Liu, Thermodynamic Modeling of the Binary Barium–Oxygen System, Journal of the American Ceramic Society 88, 1943-1948 (2005).
assessment that models this phase

GAS (Ba–O)

Id: phase:ba-o:gas; status assigned
Structure: gas; type st:gas; gas; confidence high
Stability: stable in 1 of 1 calculated diagram(s): 301.02–2500 K, x(O) 0–1
Literature: 4 values (4 accepted) from 1 papers
Interactive: phase registry entry

Names (6): corpus: corpus:phase:ba-o:gas
paper: paper:10.1111/j.1551-2916.2005.00368.x:Gas, paper:10.1111/j.1551-2916.2005.00368.x:gas
tdb: tdb:BaO-05Zho-mod.tdb:GAS, tdb:BaO-05Zho.tdb:GAS, tdb:BaO-95Zim.tdb:GAS

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

BaO-05Zho-mod.tdb: GAS, type code %, sha256 1166f495f723a413…

92: PHASE GAS:G % 1 1 !
93: CONST GAS:G : BA BA2 BA2O BAO O O2 O3 : !

BaO-05Zho.tdb: GAS, type code %, sha256 c272fdb1966d275b…

78: PHASE GAS:G % 1 1 !
79: CONST GAS:G : BA BA2 BA2O BAO O O2 O3 : !

BaO-95Zim.tdb: GAS, type code %, sha256 a0f7658f38a4a7d7…

57: PHASE GAS:G % 1 1 !
58: CONST GAS:G : BA BA2 BA2O BAO BA2O2 O O2 O3 : !

Example references (2 of 2; assessments first):

doi:10.1111/j.1551-2916.2005.00368.x Shihuai Zhou, Raymundo Arroyave, Clive A. Randall, Zi‐Kui Liu, Thermodynamic Modeling of the Binary Barium–Oxygen System, Journal of the American Ceramic Society 88, 1943-1948 (2005).
assessment that models this phase; reports values for this phase
doi:10.1016/0364-5916(95)00012-4 E. Zimmermann, K. Hack, D. Neuschütz, Thermochemical assessment of the binary system Ba-O, Calphad 19, 119-127 (1995).
assessment that models this phase

HCP_A3 (Ba–O)

Id: phase:ba-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: Ba 1.0000
Stability: not stable in 1 calculated diagram(s)
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (4): corpus: corpus:phase:ba-o:hcp-a3
tdb: tdb:BaO-05Zho-mod.tdb:HCP_A3, tdb:BaO-05Zho.tdb:HCP_A3, tdb:BaO-95Zim.tdb:HCP_A3

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

BaO-05Zho-mod.tdb: HCP_A3, type code %A, sha256 1166f495f723a413…

70: PHASE HCP_A3 %A 2 1 0.5 !
71: CONST HCP_A3 : BA : VA : !

BaO-05Zho.tdb: HCP_A3, type code %A, sha256 c272fdb1966d275b…

56: PHASE HCP_A3 %A 2 1 0.5 !
57: CONST HCP_A3 : BA : VA : !

BaO-95Zim.tdb: HCP_A3, type code %A, sha256 a0f7658f38a4a7d7…

45: PHASE HCP_A3 %A 2 1 0.5 !
46: CONST HCP_A3 : BA : VA : !

Example references (2 of 2; assessments first):

doi:10.1016/0364-5916(95)00012-4 E. Zimmermann, K. Hack, D. Neuschütz, Thermochemical assessment of the binary system Ba-O, Calphad 19, 119-127 (1995).
assessment that models this phase
doi:10.1111/j.1551-2916.2005.00368.x Shihuai Zhou, Raymundo Arroyave, Clive A. Randall, Zi‐Kui Liu, Thermodynamic Modeling of the Binary Barium–Oxygen System, Journal of the American Ceramic Society 88, 1943-1948 (2005).
assessment that models this phase

ION (Ba–O)

Id: phase:ba-o:ion; status assigned
Structure: liquid; type st:liquid; liquid; confidence high
Stability: no calculated diagram
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (3): corpus: corpus:phase:ba-o:ion
tdb: tdb:BaO-05Zho-mod.tdb:ION, tdb:BaO-05Zho.tdb:ION

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

BaO-05Zho-mod.tdb: ION, type code %, sha256 1166f495f723a413…

55: PHASE ION:Y % 2 1 1 !
56: CONST ION:Y : BA+2 : O-2 VA : !

BaO-05Zho.tdb: ION, type code %, sha256 c272fdb1966d275b…

41: PHASE ION:Y % 2 1 1 !
42: CONST ION:Y : BA+2 : O-2 O2-2 VA : !

Example references (1 of 1; assessments first):

doi:10.1111/j.1551-2916.2005.00368.x Shihuai Zhou, Raymundo Arroyave, Clive A. Randall, Zi‐Kui Liu, Thermodynamic Modeling of the Binary Barium–Oxygen System, Journal of the American Ceramic Society 88, 1943-1948 (2005).
assessment that models this phase

LIQUID (Ba–O)

Id: phase:ba-o:liquid; status assigned
Structure: liquid; type st:liquid; liquid; confidence high
Stability: stable in 1 of 1 calculated diagram(s): 854.47–2500 K, x(O) 0–0.56843
Literature: 6 values (6 accepted) from 1 papers
Interactive: phase registry entry

Names (4): corpus: corpus:phase:ba-o:liquid
paper: paper:10.1111/j.1551-2916.2005.00368.x:L, paper:10.1111/j.1551-2916.2005.00368.x:liquid
tdb: tdb:BaO-95Zim.tdb:LIQUID

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

BaO-95Zim.tdb: LIQUID, type code %, sha256 a0f7658f38a4a7d7…

30: PHASE LIQUID:L % 1 1 !
31: CONST LIQUID:L : BA BAO O : !

Example references (2 of 2; assessments first):

doi:10.1016/0364-5916(95)00012-4 E. Zimmermann, K. Hack, D. Neuschütz, Thermochemical assessment of the binary system Ba-O, Calphad 19, 119-127 (1995).
assessment that models this phase
doi:10.1111/j.1551-2916.2005.00368.x Shihuai Zhou, Raymundo Arroyave, Clive A. Randall, Zi‐Kui Liu, Thermodynamic Modeling of the Binary Barium–Oxygen System, Journal of the American Ceramic Society 88, 1943-1948 (2005).
reports values for this phase

O2GAS (Ba–O)

Id: phase:ba-o:o2gas; status assigned
Structure: gas; type st:gas; gas; confidence high
Stability: stable in 1 of 1 calculated diagram(s): 300–1181.02 K, x(O) 1–1
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (4): corpus: corpus:phase:ba-o:o2gas
tdb: tdb:BaO-05Zho-mod.tdb:O2GAS, tdb:BaO-05Zho.tdb:O2GAS, tdb:BaO-95Zim.tdb:O2GAS

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

BaO-05Zho-mod.tdb: O2GAS, type code %, sha256 1166f495f723a413…

89: PHASE O2GAS % 1 1 !
90: CONST O2GAS : O2 :!

BaO-05Zho.tdb: O2GAS, type code %, sha256 c272fdb1966d275b…

75: PHASE O2GAS % 1 1 !
76: CONST O2GAS : O2 :!

BaO-95Zim.tdb: O2GAS, type code %, sha256 a0f7658f38a4a7d7…

54: PHASE O2GAS % 1 1 !
55: CONST O2GAS : O2 :!

Example references (2 of 2; assessments first):

doi:10.1016/0364-5916(95)00012-4 E. Zimmermann, K. Hack, D. Neuschütz, Thermochemical assessment of the binary system Ba-O, Calphad 19, 119-127 (1995).
assessment that models this phase
doi:10.1111/j.1551-2916.2005.00368.x Shihuai Zhou, Raymundo Arroyave, Clive A. Randall, Zi‐Kui Liu, Thermodynamic Modeling of the Binary Barium–Oxygen System, Journal of the American Ceramic Society 88, 1943-1948 (2005).
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}
}