Mg–O phases

8 phases (tier A 4, liquid 2, gas 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 · Mg–O system page · Markdown · field reference

Phases of the Mg–O system (8)
Phase	Structure	Basis	Stability (calculated)	Literature values	TDB models
B1_OXIDE phase:mg-o:b1-oxide	NaCl · B1 · cF8 · Fm-3m (225)	tier A: standard phase name	stable in 2 of 2 calculated diagram(s): 300–2500 K, x(O) 0.5–0.5	14	3
BCC_A2 phase:mg-o:bcc-a2	W · A2 · cI2 · Im-3m (229)	tier A: standard phase name	not stable in 2 calculated diagram(s)	0	3
FCC_A1 phase:mg-o:fcc-a1	Cu · A1 · cF4 · Fm-3m (225)	tier A: standard phase name	not stable in 2 calculated diagram(s)	0	3
GAS phase:mg-o:gas	gas	gas	stable in 2 of 2 calculated diagram(s): 1372.5–2500 K, x(O) 0–1	0	3
HCP_A3 phase:mg-o:hcp-a3	Mg · A3 · hP2 · P6_3/mmc (194)	tier A: standard phase name	stable in 2 of 2 calculated diagram(s): 300–925 K, x(O) 0–0	0	3
ION phase:mg-o:ion	liquid	liquid	stable in 1 of 2 calculated diagram(s): 922–925 K, x(O) 0–0.0012	0	3
LIQUID phase:mg-o:liquid	liquid	liquid	not stable in 2 calculated diagram(s)	27	3
O2GAS phase:mg-o:o2gas	gas	gas	stable in 2 of 2 calculated diagram(s): 300–797.5 K, x(O) 1–1	0	3

B1_OXIDE (Mg–O)

Id: phase:mg-o:b1-oxide; status assigned
Structure: NaCl · B1 · cF8 · Fm-3m (225); type st:b1-nacl-cf8; tier A: standard phase name; confidence high
Stability: stable in 2 of 2 calculated diagram(s): 300–2500 K, x(O) 0.5–0.5
Literature: 14 values (14 accepted) from 1 papers
Interactive: phase registry entry

Names (5): corpus: corpus:phase:mg-o:b1-oxide
paper: paper:10.1016/j.jeurceramsoc.2018.06.015:MgO
tdb: tdb:MgO-18Lia.tdb:B1_OXIDE, tdb:MgO-23Li.tdb:B1_OXIDE, tdb:MgO-93Hal-LB.tdb:B1_OXIDE

TDB models of B1_OXIDE (3): PHASE and CONSTITUENT statements as written

MgO-18Lia.tdb: B1_OXIDE, type code %, sha256 28bd068049e41b57…

62: PHASE B1_OXIDE:I % 2 1 1 !
63: CONST B1_OXIDE:I : MG+2 : O-2 : !

MgO-23Li.tdb: B1_OXIDE, type code %, sha256 d795b07d34aedd0d…

56: PHASE B1_OXIDE:I % 2 1 1 !
57: CONST B1_OXIDE:I : MG+2 : O-2 : !

MgO-93Hal-LB.tdb: B1_OXIDE, type code %, sha256 b656673952720e19…

63: PHASE B1_OXIDE:I % 2 1 1 !
64: CONST B1_OXIDE:I : MG+2 : O-2 : !

Example references (10 of 10; assessments first):

doi:10.1016/j.jeurceramsoc.2018.06.015 Song-Mao Liang, Rainer Schmid-Fetzer, Complete thermodynamic description of the Mg-Ca-O phase diagram including the Ca-O, Mg-O and CaO-MgO subsystems, Journal of the European Ceramic Society 38, 4768-4785 (2018).
assessment that models this phase; reports values for this phase
doi:10.1016/0364-5916(93)90006-W B. Hallstedt, Calphad, 17, 281-86(1993).
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
doi:10.1351/pac198254030681 J. Hlavac, Melting temperatures of refractory oxides: Part I, Pure and Applied Chemistry 54, 681-688 (1982).
cited as the source of values for this phase
doi:10.1002/zaac.19130820131 Otto Ruff, Arbeiten im Gebiet hoher Temperaturen I. Über das Schmelzen und Verdampfen unserer feuerbeständigsten Oxyde im elektrischen Vakuumofen, Z. Anorg. Chem. 82, 373-400 (1913).
cited as the source of values for this phase
doi:10.1007/bf02874914 H. A. Wriedt, The Mg−O (Magnesium-Oxygen) system, Bulletin of Alloy Phase Diagrams 8, 227-233 (1987).
cited as the source of values for this phase
doi:10.1016/0016-7037(87)90009-3 Milton Blander, Arthur D. Pelton, Thermodynamic analysis of binary liquid silicates and prediction of ternary solution properties by modified quasichemical equations, Geochimica et Cosmochimica Acta 51, 85-95 (1987).
cited as the source of values for this phase
doi:10.1016/0040-6031(93)80422-7 A.P. Chernyshev, V.A. Petrov, V.E. Titov, A.Yu. Vorobyev, Thermal radiative properties of magnesium oxide at high temperatures, Thermochimica Acta 218, 195-209 (1993).
cited as the source of values for this phase
doi:10.1016/0364-5916(89)90006-0 M. Hillert, X. Wang, Thermodynamic calculation of the CaO–MgO system, Calphad 13 (1989) 267–271, http://dx.doi.org/10.1016/0364-5916(89)90006-0.
cited as the source of values for this phase
doi:10.1063/1.1398069 Claudio Ronchi, Mikhail Sheindlin, Melting point of MgO, Journal of Applied Physics 90, 3325-3331 (2001).
cited as the source of values for this phase

BCC_A2 (Mg–O)

Id: phase:mg-o:bcc-a2; status assigned
Structure: W · A2 · cI2 · Im-3m (229); type st:a2-w-ci2; tier A: standard phase name; confidence high
Stability: not stable in 2 calculated diagram(s)
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (4): corpus: corpus:phase:mg-o:bcc-a2
tdb: tdb:MgO-18Lia.tdb:BCC_A2, tdb:MgO-23Li.tdb:BCC_A2, tdb:MgO-93Hal-LB.tdb:BCC_A2

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

MgO-18Lia.tdb: BCC_A2, type code %B, sha256 28bd068049e41b57…

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

MgO-23Li.tdb: BCC_A2, type code %B, sha256 d795b07d34aedd0d…

46: PHASE BCC_A2 %B 2 1 3 !
47: CONST BCC_A2 : MG : VA : !

MgO-93Hal-LB.tdb: BCC_A2, type code %B, sha256 b656673952720e19…

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

Example references (3 of 3; assessments first):

doi:10.1016/0364-5916(93)90006-W B. Hallstedt, Calphad, 17, 281-86(1993).
assessment that models this phase
doi:10.1016/j.jeurceramsoc.2018.06.015 Song-Mao Liang, Rainer Schmid-Fetzer, Complete thermodynamic description of the Mg-Ca-O phase diagram including the Ca-O, Mg-O and CaO-MgO subsystems, Journal of the European Ceramic Society 38, 4768-4785 (2018).
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

FCC_A1 (Mg–O)

Id: phase:mg-o:fcc-a1; status assigned
Structure: Cu · A1 · cF4 · Fm-3m (225); type st:a1-cu-cf4; tier A: standard phase name; confidence high
Stability: not stable in 2 calculated diagram(s)
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (4): corpus: corpus:phase:mg-o:fcc-a1
tdb: tdb:MgO-18Lia.tdb:FCC_A1, tdb:MgO-23Li.tdb:FCC_A1, tdb:MgO-93Hal-LB.tdb:FCC_A1

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

MgO-18Lia.tdb: FCC_A1, type code %A, sha256 28bd068049e41b57…

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

MgO-23Li.tdb: FCC_A1, type code %A, sha256 d795b07d34aedd0d…

41: PHASE FCC_A1 %A 2 1 1 !
42: CONST FCC_A1 : MG : VA : !

MgO-93Hal-LB.tdb: FCC_A1, type code %A, sha256 b656673952720e19…

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

Example references (3 of 3; assessments first):

doi:10.1016/0364-5916(93)90006-W B. Hallstedt, Calphad, 17, 281-86(1993).
assessment that models this phase
doi:10.1016/j.jeurceramsoc.2018.06.015 Song-Mao Liang, Rainer Schmid-Fetzer, Complete thermodynamic description of the Mg-Ca-O phase diagram including the Ca-O, Mg-O and CaO-MgO subsystems, Journal of the European Ceramic Society 38, 4768-4785 (2018).
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 (Mg–O)

Id: phase:mg-o:gas; status assigned
Structure: gas; type st:gas; gas; confidence high
Stability: stable in 2 of 2 calculated diagram(s): 1372.5–2500 K, x(O) 0–1
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (4): corpus: corpus:phase:mg-o:gas
tdb: tdb:MgO-18Lia.tdb:GAS, tdb:MgO-23Li.tdb:GAS, tdb:MgO-93Hal-LB.tdb:GAS

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

MgO-18Lia.tdb: GAS, type code %, sha256 28bd068049e41b57…

65: PHASE GAS:G % 1 1 !
66: CONST GAS:G : MG MG2 MGO O O2% O3 : !

MgO-23Li.tdb: GAS, type code %, sha256 d795b07d34aedd0d…

59: PHASE GAS:G % 1 1 !
60: CONST GAS:G : MG MG2 MGO O O2% O3 : !

MgO-93Hal-LB.tdb: GAS, type code %, sha256 b656673952720e19…

66: PHASE GAS:G % 1 1 !
67: CONST GAS:G : MG MG2 MGO O O2% O3 : !

Example references (3 of 3; assessments first):

doi:10.1016/0364-5916(93)90006-W B. Hallstedt, Calphad, 17, 281-86(1993).
assessment that models this phase
doi:10.1016/j.jeurceramsoc.2018.06.015 Song-Mao Liang, Rainer Schmid-Fetzer, Complete thermodynamic description of the Mg-Ca-O phase diagram including the Ca-O, Mg-O and CaO-MgO subsystems, Journal of the European Ceramic Society 38, 4768-4785 (2018).
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 (Mg–O)

Id: phase:mg-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
Stability: stable in 2 of 2 calculated diagram(s): 300–925 K, x(O) 0–0
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (4): corpus: corpus:phase:mg-o:hcp-a3
tdb: tdb:MgO-18Lia.tdb:HCP_A3, tdb:MgO-23Li.tdb:HCP_A3, tdb:MgO-93Hal-LB.tdb:HCP_A3

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

MgO-18Lia.tdb: HCP_A3, type code %A, sha256 28bd068049e41b57…

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

MgO-23Li.tdb: HCP_A3, type code %A, sha256 d795b07d34aedd0d…

51: PHASE HCP_A3 %A 2 1 0.5 !
52: CONST HCP_A3 : MG : VA : !

MgO-93Hal-LB.tdb: HCP_A3, type code %A, sha256 b656673952720e19…

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

Example references (3 of 3; assessments first):

doi:10.1016/0364-5916(93)90006-W B. Hallstedt, Calphad, 17, 281-86(1993).
assessment that models this phase
doi:10.1016/j.jeurceramsoc.2018.06.015 Song-Mao Liang, Rainer Schmid-Fetzer, Complete thermodynamic description of the Mg-Ca-O phase diagram including the Ca-O, Mg-O and CaO-MgO subsystems, Journal of the European Ceramic Society 38, 4768-4785 (2018).
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 (Mg–O)

Id: phase:mg-o:ion; status assigned
Structure: liquid; type st:liquid; liquid; confidence high
Stability: stable in 1 of 2 calculated diagram(s): 922–925 K, x(O) 0–0.0012
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (4): corpus: corpus:phase:mg-o:ion
tdb: tdb:MgO-18Lia.tdb:ION, tdb:MgO-23Li.tdb:ION, tdb:MgO-93Hal-LB.tdb:ION

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

MgO-18Lia.tdb: ION, type code %, sha256 28bd068049e41b57…

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

MgO-23Li.tdb: ION, type code %, sha256 d795b07d34aedd0d…

33: PHASE ION:Y % 2 1 1 !
34: CONST ION:Y : MG+2 : O-2 VA : !

MgO-93Hal-LB.tdb: ION, type code %, sha256 b656673952720e19…

40: PHASE ION:Y % 2 1 1 !
41: CONST ION:Y : MG+2 : O-2 VA : !

Example references (3 of 3; assessments first):

doi:10.1016/0364-5916(93)90006-W B. Hallstedt, Calphad, 17, 281-86(1993).
assessment that models this phase
doi:10.1016/j.jeurceramsoc.2018.06.015 Song-Mao Liang, Rainer Schmid-Fetzer, Complete thermodynamic description of the Mg-Ca-O phase diagram including the Ca-O, Mg-O and CaO-MgO subsystems, Journal of the European Ceramic Society 38, 4768-4785 (2018).
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 (Mg–O)

Id: phase:mg-o:liquid; status assigned
Structure: liquid; type st:liquid; liquid; confidence high
Stability: not stable in 2 calculated diagram(s)
Literature: 27 values (27 accepted) from 2 papers
Interactive: phase registry entry

Names (6): corpus: corpus:phase:mg-o:liquid
paper: paper:10.1016/0364-5916(93)90006-w:liquid Mg, paper:10.1016/j.jeurceramsoc.2018.06.015:liquid
tdb: tdb:MgO-18Lia.tdb:LIQUID, tdb:MgO-23Li.tdb:LIQUID, tdb:MgO-93Hal-LB.tdb:LIQUID

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

MgO-18Lia.tdb: LIQUID, type code %, sha256 28bd068049e41b57…

42: PHASE LIQUID:L % 1 1 !
43: CONST LIQUID:L : MG MGO O : !

MgO-23Li.tdb: LIQUID, type code %, sha256 d795b07d34aedd0d…

36: PHASE LIQUID:L % 1 1 !
37: CONST LIQUID:L : MG : !

MgO-93Hal-LB.tdb: LIQUID, type code %, sha256 b656673952720e19…

43: PHASE LIQUID:L % 1 1 !
44: CONST LIQUID:L : MG : !

Example references (10 of 10; assessments first):

doi:10.1016/j.jeurceramsoc.2018.06.015 Song-Mao Liang, Rainer Schmid-Fetzer, Complete thermodynamic description of the Mg-Ca-O phase diagram including the Ca-O, Mg-O and CaO-MgO subsystems, Journal of the European Ceramic Society 38, 4768-4785 (2018).
assessment that models this phase; reports values for this phase
doi:10.1016/0364-5916(93)90006-W B. Hallstedt, Calphad, 17, 281-86(1993).
assessment that models this phase; reports values for 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
doi:10.1351/pac198254030681 J. Hlavac, Melting temperatures of refractory oxides: Part I, Pure and Applied Chemistry 54, 681-688 (1982).
cited as the source of values for this phase
doi:10.1002/zaac.19130820131 Otto Ruff, Arbeiten im Gebiet hoher Temperaturen I. Über das Schmelzen und Verdampfen unserer feuerbeständigsten Oxyde im elektrischen Vakuumofen, Z. Anorg. Chem. 82, 373-400 (1913).
cited as the source of values for this phase
doi:10.1007/bf02874914 H. A. Wriedt, The Mg−O (Magnesium-Oxygen) system, Bulletin of Alloy Phase Diagrams 8, 227-233 (1987).
cited as the source of values for this phase
doi:10.1016/0016-7037(87)90009-3 Milton Blander, Arthur D. Pelton, Thermodynamic analysis of binary liquid silicates and prediction of ternary solution properties by modified quasichemical equations, Geochimica et Cosmochimica Acta 51, 85-95 (1987).
cited as the source of values for this phase
doi:10.1016/0040-6031(93)80422-7 A.P. Chernyshev, V.A. Petrov, V.E. Titov, A.Yu. Vorobyev, Thermal radiative properties of magnesium oxide at high temperatures, Thermochimica Acta 218, 195-209 (1993).
cited as the source of values for this phase
doi:10.1016/0364-5916(89)90006-0 M. Hillert, X. Wang, Thermodynamic calculation of the CaO–MgO system, Calphad 13 (1989) 267–271, http://dx.doi.org/10.1016/0364-5916(89)90006-0.
cited as the source of values for this phase
doi:10.1063/1.1398069 Claudio Ronchi, Mikhail Sheindlin, Melting point of MgO, Journal of Applied Physics 90, 3325-3331 (2001).
cited as the source of values for this phase

O2GAS (Mg–O)

Id: phase:mg-o:o2gas; status assigned
Structure: gas; type st:gas; gas; confidence high
Stability: stable in 2 of 2 calculated diagram(s): 300–797.5 K, x(O) 1–1
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (4): corpus: corpus:phase:mg-o:o2gas
tdb: tdb:MgO-18Lia.tdb:O2GAS, tdb:MgO-23Li.tdb:O2GAS, tdb:MgO-93Hal-LB.tdb:O2GAS

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

MgO-18Lia.tdb: O2GAS, type code %, sha256 28bd068049e41b57…

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

MgO-23Li.tdb: O2GAS, type code %, sha256 d795b07d34aedd0d…

62: PHASE O2GAS % 1 1 !
63: CONST O2GAS : O2 : !

MgO-93Hal-LB.tdb: O2GAS, type code %, sha256 b656673952720e19…

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

Example references (3 of 3; assessments first):

doi:10.1016/0364-5916(93)90006-W B. Hallstedt, Calphad, 17, 281-86(1993).
assessment that models this phase
doi:10.1016/j.jeurceramsoc.2018.06.015 Song-Mao Liang, Rainer Schmid-Fetzer, Complete thermodynamic description of the Mg-Ca-O phase diagram including the Ca-O, Mg-O and CaO-MgO subsystems, Journal of the European Ceramic Society 38, 4768-4785 (2018).
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}
}