Bi–O phases

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

Phases of the Bi–O system (6)
Phase	Structure	Basis	Stability (calculated)	Literature values	TDB models
RHOMBOHEDRAL_A7 phase:bi-o:a7-rhombohedral	alpha-As · A7 · hR2 · R-3m (166)	tier A: standard phase name	stable in 1 of 1 calculated diagram(s): 300–544.55 K, x(O) 0–0	1	1
BI2O3_ALPHA phase:bi-o:bi2o3-alpha	alpha-Bi2O3 · mP20 · P2_1/c (14)	tier C: assessor-stated (Hallstedt 2025 crystallographic table)	stable in 1 of 1 calculated diagram(s): 300–1002.13 K, x(O) 0.6–0.6	34	1
BI2O3_C1 phase:bi-o:bi2o3-c1	CaF2 · C1 · cF12 · Fm-3m (225)	tier A: standard phase name	stable in 1 of 1 calculated diagram(s): 1002.13–1060.59 K, x(O) 0.6–0.6	25	1
GAS phase:bi-o:gas	gas	gas	stable in 1 of 1 calculated diagram(s): 1825.76–1966.02 K, x(O) 0–0.92757	0	1
ION phase:bi-o:ion	liquid	liquid	stable in 1 of 1 calculated diagram(s): 544.55–1966.02 K, x(O) 0–0.59458	25	1
O2GAS phase:bi-o:o2gas	gas	gas	stable in 1 of 1 calculated diagram(s): 300–925 K, x(O) 1–1	0	1

RHOMBOHEDRAL_A7 (Bi–O)

Id: phase:bi-o:a7-rhombohedral; status assigned
Structure: alpha-As · A7 · hR2 · R-3m (166); type st:a7-alpha-as-hr2; tier A: standard phase name; confidence high
Stoichiometry: Bi 1.0000
Stability: stable in 1 of 1 calculated diagram(s): 300–544.55 K, x(O) 0–0
Literature: 1 values (1 accepted) from 1 papers
Interactive: phase registry entry

Names (3): corpus: corpus:phase:bi-o:a7-rhombohedral
paper: paper:10.1007/bf02667306:Bi
tdb: tdb:BiO-95Ris-LB.tdb:RHOMBOHEDRAL_A7

TDB models of RHOMBOHEDRAL_A7 (1): PHASE and CONSTITUENT statements as written

BiO-95Ris-LB.tdb: RHOMBOHEDRAL_A7, type code %, sha256 77661bfd1c983207…

47: PHASE RHOMBOHEDRAL_A7 % 1 1 !
48: CONST RHOMBOHEDRAL_A7 : BI : !

Example references (1 of 1; assessments first):

doi:10.1007/BF02667306 D. Risold, B. Hallstedt, L.J. Gauckler, H.L. Lukas, S.G. Fries, J. Phase Equilib., 16, 223-34(1995).
assessment that models this phase; reports values for this phase

BI2O3_ALPHA (Bi–O)

Id: phase:bi-o:bi2o3-alpha; status assigned
Structure: alpha-Bi2O3 · mP20 · P2_1/c (14); type st:alpha-bi2o3-mp20; 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 (no_structure_token, off_stoichiometric_model); structure as stated in the SGTE crystallographic table for this phase name and system
Stability: stable in 1 of 1 calculated diagram(s): 300–1002.13 K, x(O) 0.6–0.6
Literature: 34 values (34 accepted) from 1 papers
Interactive: phase registry entry

Names (5): corpus: corpus:phase:bi-o:bi2o3-alpha
paper: paper:10.1007/bf02667306:α, paper:10.1007/bf02667306:α, δ, paper:10.1007/bf02667306:α-Bi2O3
tdb: tdb:BiO-95Ris-LB.tdb:BI2O3_ALPHA

TDB models of BI2O3_ALPHA (1): PHASE and CONSTITUENT statements as written

BiO-95Ris-LB.tdb: BI2O3_ALPHA, type code %, sha256 77661bfd1c983207…

52: PHASE BI2O3_ALPHA % 1 1 !
53: CONST BI2O3_ALPHA : BI2O3 : !

Example references (10 of 10; assessments first):

doi:10.1007/BF02667306 D. Risold, B. Hallstedt, L.J. Gauckler, H.L. Lukas, S.G. Fries, J. Phase Equilib., 16, 223-34(1995).
assessment that models this phase; reports values for this phase
doi:10.1016/0036-9748(71)90168-2 A.V. Ramana Rao, V.B. Tare, Free energy of formation of Bi2O3, Scripta Metallurgica 5, 807-811 (1971).
cited as the source of values for this phase
doi:10.1016/0040-6031(80)87127-9 Krzysztop Fitzner, Diffusivity, activity and solubility of oxygen in liquid bismuth, Thermochimica Acta 35, 277-286 (1980).
cited as the source of values for this phase
doi:10.1149/1.2403593 D. Chatterji, J. V. Smith, Free Energy of Formation of Bi[sub 2]O[sub 3], Sb[sub 2]O[sub 3], and TeO[sub 2] from EMF Measurements, J. Electrochem. Soc. 120, 889 (1973).
cited as the source of values for this phase
doi:10.2320/jinstmet1952.55.5_536 Kazuo Kameda, Katsunori Yamaguchi, Activity Measurements of Liquid Ag-Bi Alloys by an EMF Method Using a Zirconia Electrolyte, J.Japan Inst.Metals 55, 536-544 (1991).
cited as the source of values for this phase
doi:10.2320/jinstmet1952.56.8_900 Kazuo Kameda, Katsunori Yamaguchi, Toshiko Kon, Activity of Liquid Tl-Bi Alloys Measured by an EMF Method Using Zirconia Electrolyte, J.Japan Inst.Metals 56, 900-906 (1992).
cited as the source of values for this phase
doi:10.1002/zaac.19623180307 G. Gattow, H. Schröder, Über Wismutoxide. III. Die Kristallstruktur der Hochtemperaturmodifikation von Wismut(III)‐oxid (δ‐Bi2O3), Zeitschrift anorg allge chemie 318, 176-189 (1962).
cited as the source of values for this phase
doi:10.1021/j100723a031 C. N. Ramachandra Rao, G. V. Subba Rao, S. Ramdas, Phase transformations and electrical properties of bismuth sesquioxide, J. Phys. Chem. 73, 672-675 (1969).
cited as the source of values for this phase
doi:10.1021/je60035a021 Daniel Cubicciotti, Harold Eding, Enthalpy and entropy increments above 298.degree.K. for bismuth(III) bromide, bismuth(III) oxide, thallium(III) oxide, and thallium(I) oxide, J. Chem. Eng. Data 12, 548-551 (1967).
cited as the source of values for this phase
doi:10.6028/jres.069a.023 Ernest M. Levin, Clyde L. McDaniel, Heats of transformations in bismuth oxide by differential thermal analysis, J. RES. NATL. BUR. STAN. SECT. A. 69A, 237 (1965).
cited as the source of values for this phase

BI2O3_C1 (Bi–O)

Id: phase:bi-o:bi2o3-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): 1002.13–1060.59 K, x(O) 0.6–0.6
Literature: 25 values (25 accepted) from 1 papers
Interactive: phase registry entry

Names (3): corpus: corpus:phase:bi-o:bi2o3-c1
paper: paper:10.1007/bf02667306:δ-Bi2O3
tdb: tdb:BiO-95Ris-LB.tdb:BI2O3_C1

TDB models of BI2O3_C1 (1): PHASE and CONSTITUENT statements as written

BiO-95Ris-LB.tdb: BI2O3_C1, type code %, sha256 77661bfd1c983207…

57: PHASE BI2O3_C1 % 1 1 !
58: CONST BI2O3_C1 : BI2O3 : !

Example references (10 of 10; assessments first):

doi:10.1007/BF02667306 D. Risold, B. Hallstedt, L.J. Gauckler, H.L. Lukas, S.G. Fries, J. Phase Equilib., 16, 223-34(1995).
assessment that models this phase; reports values for this phase
doi:10.1021/je60035a021 Daniel Cubicciotti, Harold Eding, Enthalpy and entropy increments above 298.degree.K. for bismuth(III) bromide, bismuth(III) oxide, thallium(III) oxide, and thallium(I) oxide, J. Chem. Eng. Data 12, 548-551 (1967).
cited as the source of values for this phase
doi:10.6028/jres.069a.023 Ernest M. Levin, Clyde L. McDaniel, Heats of transformations in bismuth oxide by differential thermal analysis, J. RES. NATL. BUR. STAN. SECT. A. 69A, 237 (1965).
cited as the source of values for this phase
doi:10.1002/zaac.19623180307 G. Gattow, H. Schröder, Über Wismutoxide. III. Die Kristallstruktur der Hochtemperaturmodifikation von Wismut(III)‐oxid (δ‐Bi2O3), Zeitschrift anorg allge chemie 318, 176-189 (1962).
cited as the source of values for this phase
doi:10.1002/zaac.19643280106 G. Gattow, D. Schütze, Über Wismutoxide. VI. Überein Wismut (III)‐oxid mit höherem Sauerstoffgehalt (β‐Modifikation), Zeitschrift anorg allge chemie 328, 44-68 (1964).
cited as the source of values for this phase
doi:10.1016/0036-9748(71)90168-2 A.V. Ramana Rao, V.B. Tare, Free energy of formation of Bi2O3, Scripta Metallurgica 5, 807-811 (1971).
cited as the source of values for this phase
doi:10.1016/0040-6031(80)87127-9 Krzysztop Fitzner, Diffusivity, activity and solubility of oxygen in liquid bismuth, Thermochimica Acta 35, 277-286 (1980).
cited as the source of values for this phase
doi:10.1021/j100723a031 C. N. Ramachandra Rao, G. V. Subba Rao, S. Ramdas, Phase transformations and electrical properties of bismuth sesquioxide, J. Phys. Chem. 73, 672-675 (1969).
cited as the source of values for this phase
doi:10.2320/jinstmet1952.55.5_536 Kazuo Kameda, Katsunori Yamaguchi, Activity Measurements of Liquid Ag-Bi Alloys by an EMF Method Using a Zirconia Electrolyte, J.Japan Inst.Metals 55, 536-544 (1991).
cited as the source of values for this phase
doi:10.2320/jinstmet1952.56.8_900 Kazuo Kameda, Katsunori Yamaguchi, Toshiko Kon, Activity of Liquid Tl-Bi Alloys Measured by an EMF Method Using Zirconia Electrolyte, J.Japan Inst.Metals 56, 900-906 (1992).
cited as the source of values for this phase

GAS (Bi–O)

Id: phase:bi-o:gas; status assigned
Structure: gas; type st:gas; gas; confidence high
Stability: stable in 1 of 1 calculated diagram(s): 1825.76–1966.02 K, x(O) 0–0.92757
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (2): corpus: corpus:phase:bi-o:gas
tdb: tdb:BiO-95Ris-LB.tdb:GAS

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

BiO-95Ris-LB.tdb: GAS, type code %, sha256 77661bfd1c983207…

60: PHASE GAS:G % 1 1 !
61: CONST GAS:G : BI BI2 BI3 BI4 O O2 O3 
               BIO BI2O_C2V BI2O_DH BI2O2 BI2O3 BI3O4 BI4O6 : !

Example references (1 of 1; assessments first):

doi:10.1007/BF02667306 D. Risold, B. Hallstedt, L.J. Gauckler, H.L. Lukas, S.G. Fries, J. Phase Equilib., 16, 223-34(1995).
assessment that models this phase

ION (Bi–O)

Id: phase:bi-o:ion; status assigned
Structure: liquid; type st:liquid; liquid; confidence high
Stability: stable in 1 of 1 calculated diagram(s): 544.55–1966.02 K, x(O) 0–0.59458
Literature: 25 values (25 accepted) from 1 papers
Interactive: phase registry entry

Names (6): corpus: corpus:phase:bi-o:ion, corpus:phase:bi-o:ion-2, corpus:phase:bi-o:liquid
paper: paper:10.1007/bf02667306:L1, paper:10.1007/bf02667306:L2
tdb: tdb:BiO-95Ris-LB.tdb:ION

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

BiO-95Ris-LB.tdb: ION, type code %, sha256 77661bfd1c983207…

42: PHASE ION:Y % 2 1 1 !
43: CONST ION:Y : BI+3 : O-2 VA O : !

Example references (10 of 10; assessments first):

doi:10.1007/BF02667306 D. Risold, B. Hallstedt, L.J. Gauckler, H.L. Lukas, S.G. Fries, J. Phase Equilib., 16, 223-34(1995).
assessment that models this phase; reports values for this phase
doi:10.1002/zaac.19623180307 G. Gattow, H. Schröder, Über Wismutoxide. III. Die Kristallstruktur der Hochtemperaturmodifikation von Wismut(III)‐oxid (δ‐Bi2O3), Zeitschrift anorg allge chemie 318, 176-189 (1962).
cited as the source of values for this phase
doi:10.1002/zaac.19643280106 G. Gattow, D. Schütze, Über Wismutoxide. VI. Überein Wismut (III)‐oxid mit höherem Sauerstoffgehalt (β‐Modifikation), Zeitschrift anorg allge chemie 328, 44-68 (1964).
cited as the source of values for this phase
doi:10.1016/0036-9748(71)90168-2 A.V. Ramana Rao, V.B. Tare, Free energy of formation of Bi2O3, Scripta Metallurgica 5, 807-811 (1971).
cited as the source of values for this phase
doi:10.1016/0040-6031(80)87127-9 Krzysztop Fitzner, Diffusivity, activity and solubility of oxygen in liquid bismuth, Thermochimica Acta 35, 277-286 (1980).
cited as the source of values for this phase
doi:10.1021/j100723a031 C. N. Ramachandra Rao, G. V. Subba Rao, S. Ramdas, Phase transformations and electrical properties of bismuth sesquioxide, J. Phys. Chem. 73, 672-675 (1969).
cited as the source of values for this phase
doi:10.1021/je60035a021 Daniel Cubicciotti, Harold Eding, Enthalpy and entropy increments above 298.degree.K. for bismuth(III) bromide, bismuth(III) oxide, thallium(III) oxide, and thallium(I) oxide, J. Chem. Eng. Data 12, 548-551 (1967).
cited as the source of values for this phase
doi:10.2320/jinstmet1952.55.5_536 Kazuo Kameda, Katsunori Yamaguchi, Activity Measurements of Liquid Ag-Bi Alloys by an EMF Method Using a Zirconia Electrolyte, J.Japan Inst.Metals 55, 536-544 (1991).
cited as the source of values for this phase
doi:10.2320/jinstmet1952.56.8_900 Kazuo Kameda, Katsunori Yamaguchi, Toshiko Kon, Activity of Liquid Tl-Bi Alloys Measured by an EMF Method Using Zirconia Electrolyte, J.Japan Inst.Metals 56, 900-906 (1992).
cited as the source of values for this phase
doi:10.6028/jres.069a.023 Ernest M. Levin, Clyde L. McDaniel, Heats of transformations in bismuth oxide by differential thermal analysis, J. RES. NATL. BUR. STAN. SECT. A. 69A, 237 (1965).
cited as the source of values for this phase

O2GAS (Bi–O)

Id: phase:bi-o:o2gas; status assigned
Structure: gas; type st:gas; gas; confidence high
Stability: stable in 1 of 1 calculated diagram(s): 300–925 K, x(O) 1–1
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (2): corpus: corpus:phase:bi-o:o2gas
tdb: tdb:BiO-95Ris-LB.tdb:O2GAS

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

BiO-95Ris-LB.tdb: O2GAS, type code %, sha256 77661bfd1c983207…

64: PHASE O2GAS % 1 1 !
65: CONST O2GAS : O2 : !

Example references (1 of 1; assessments first):

doi:10.1007/BF02667306 D. Risold, B. Hallstedt, L.J. Gauckler, H.L. Lukas, S.G. Fries, J. Phase Equilib., 16, 223-34(1995).
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}
}