Ca–O system

61 accepted literature values from 2 paper(s) (experimental 11, model 44, DFT 6); 4 calculated phase diagram(s). 7 further extracted value(s) not accepted by the reader-agreement checks are only in the JSON/CSV.

Data: JSON · CSV · interactive explorer · interactive phase diagram · phases (9) · papers (bibliography) · Markdown

Accepted values by evidence class
Evidence class	Values
experimental	11
model	44
DFT	6

Accepted values by property group
Property group	Values
invariant reaction	2
phase transition	1
phase equilibrium	18
formation	14
heat capacity / entropy / enthalpy	26

Calculated phase diagrams

Binary phase diagrams calculated with pycalphad 0.11.2 from the SGTE binary collection (Hallstedt 2025, CC BY 4.0). Evidence class: model.

Assessments with a calculated phase diagram
TDB file	Assessment	SHA-256	Links
CaO-18Lia.tdb	S.-M. Liang, R. Schmid-Fetzer, J. Eur. Ceram. Soc., 38, 4768-85(2018). doi:10.1016/j.jeurceramsoc.2018.06.015	`78618178a1324682abe5762bf34fd20689dfc6461c02571d1f63465f606dfcc1`	viewer · TDB · JSON
CaO-20Def-3g.tdb	G. Deffrennes, N. Jakse, C.M.S. Alvares, I. Nuta, A. Pasturel, A.V. Khvan, A. Pisch, Calphad, 69, 101764(2020). doi:10.1016/j.calphad.2020.101764	`2df29e5f285a88c61920a1de0346ed6dd875de0fc237350301d09f81ab4df153`	viewer · TDB · JSON
CaO-23Abd-3g.tdb	W. Abdul, C. Mawalala, A. Pisch, M.N. Bannerman, Cem. Concr. Res., 173, 107309(2023). doi:10.1016/j.cemconres.2023.107309	`c6509b3e8c06ae7f3214e95a3bdd245dabd062bed11d4cb6bbf45398f8017220`	viewer · TDB · JSON
CaO-96Sel.tdb	M. Selleby, B. Sundman, Calphad, 20, 391-92(1996). doi:10.1016/S0364-5916(96)00039-9	`c26a22ca6d938a23c4deba75b8dd32e0968fb65a59ed515eb6d0dc508a66bcb7`	viewer · TDB · JSON

Calculated three-phase invariants (model, mole fraction of the second component)
TDB file	T (K)	Phases at the invariant
CaO-23Abd-3g.tdb	716.03	BCC_A2 (x(O) 0) + FCC_A1 (x(O) 0) + B1_OXIDE (x(O) 0.5)
CaO-96Sel.tdb	1111.39	BCC_A2 (x(O) 0) + ION (x(O) 0.00299) + B1_OXIDE (x(O) 0.5)

Convex hulls: Materials Project DFT hull · OQMD DFT hull · CALPHAD hull CaO-20Def-3g

Invariant reactions (literature)

Invariant reactions reported in the literature for the Ca–O system (2)
T (K)	Reaction / phases	Compositions (mole fraction)	Class	Source	Location	Quote
1103.2	eutectic: L -> β-Ca + CaO	L: O 0.0098	model	[1] Deffrennes 2020	Table 4, p. 21, row 2 report
1094.6	eutectic: L -> β-Ca + CaO	L: O 0.017	model	[1] Deffrennes 2020	Table 4, p. 21, row 1 report

Formation enthalpies

Literature values in kJ/mol-atom where the per-atom basis is known. DFT columns: the lowest-energy entry at the same composition (Materials Project 2026.04.13, OQMD v1.8; different energy references, never averaged), from dft_parity.json.

Enthalpies of formation, Ca–O system (14)
Phase	Compound	Value	T (K)	Class	MP DFT (kJ/mol-atom)	OQMD DFT (kJ/mol-atom)	Source	Location
CaO(cr)	CaO	-317.55 kJ/mol-atom	298.15	model	-318.981 (mp-aaaaadwf)	-308.324 (oqmd-1443085)	[1] Deffrennes 2020 cites Chase 1998	Table 3, p. 17, row 6 report
CaO(cr)	CaO	-317.55 kJ/mol-atom	298.15	model	-318.981 (mp-aaaaadwf)	-308.324 (oqmd-1443085)	[1] Deffrennes 2020 cites Lindberg 2009 doi	Table 3, p. 17, row 3 report
CaO(cr)	CaO	-317.3 kJ/mol-atom	298.15	model	-318.981 (mp-aaaaadwf)	-308.324 (oqmd-1443085)	[1] Deffrennes 2020	Table 3, p. 17, row 1 report
CaO(cr)		-317.3 kJ/mol-atom	298.15	DFT			[1] Deffrennes 2020 cites Pisch	Table 3, p. 17, row 5 report
CaO(cr)	CaO	-317 kJ/mol-atom	298.15	model	-318.981 (mp-aaaaadwf)	-308.324 (oqmd-1443085)	[1] Deffrennes 2020 cites Liang 2018 doi	Table 3, p. 17, row 2 report
CaO(cr)	CaO	-317 kJ/mol-atom ± 0.75	298.15	model	-318.981 (mp-aaaaadwf)	-308.324 (oqmd-1443085)	[1] Deffrennes 2020 cites Liang 2018 doi	Table 3, p. 17, row 4 report
CaO(liq-am)		-300.45 kJ/mol-atom	298.15	model			[1] Deffrennes 2020	Table 3, p. 17, row 7 report
CaO(liq-am)		-282.8 kJ/mol-atom	298.15	model			[1] Deffrennes 2020 cites Liang 2018 doi	Table 3, p. 17, row 8 report
CaO(liq-am)		-278.65 kJ/mol-atom	298.15	model			[1] Deffrennes 2020 cites Chase 1998	Table 3, p. 17, row 10 report
CaO(liq-am)		-277.8 kJ/mol-atom	298.15	model			[1] Deffrennes 2020 cites Lindberg 2009 doi	Table 3, p. 17, row 9 report
CaO2(cr)	CaO2	-219.667 kJ/mol-atom	298.15	model	-212.9 (mp-aaabkddr)	-219.972 (oqmd-1367693)	[1] Deffrennes 2020 cites Lindberg 2009 doi	Table 3, p. 17, row 13 report
CaO2(cr)	CaO2	-217.567 kJ/mol-atom	298.15	model	-212.9 (mp-aaabkddr)	-219.972 (oqmd-1367693)	[1] Deffrennes 2020 cites Liang 2018 doi	Table 3, p. 17, row 12 report
CaO2(cr)		-216.033 kJ/mol-atom	298.15	DFT			[1] Deffrennes 2020 cites Pisch	Table 3, p. 17, row 14 report
CaO2(cr)	CaO2	-216.033 kJ/mol-atom	298.15	model	-212.9 (mp-aaabkddr)	-219.972 (oqmd-1367693)	[1] Deffrennes 2020	Table 3, p. 17, row 11 report

Other properties

Phase transition (1)

Phase transition, Ca–O system
Property	Value	T (K)	Phases / composition	Class	Source	Location	Quote
Phase transition	3221.8 K	3221.8	congruent transformation	model	[2] Liang 2018	p. 14 report	However, in the binary Ca-O system the congruent melting point of CaO occurs at 3221.8 K.

Phase equilibrium (18)

Phase equilibrium, Ca–O system
Property	T (K)	Phases / composition	Class	Source	Location
Phase composition	2843	congruent melting: CaO liquid: O 0.5; CaO: O 0.5	experimental	[2] Liang 2018 cites Kanolt 1913	Table 2, p. 5, row 1 report
Phase composition	2845	congruent melting: CaO liquid: O 0.5; CaO: O 0.5	model	[2] Liang 2018 cites Factsage 2017	Table 2, p. 5, row 16 report
Phase composition	2849	congruent melting: CaO liquid: O 0.5; CaO: O 0.5	experimental	[2] Liang 2018 cites Schumacher 1926 doi	Table 2, p. 5, row 2 report
Phase composition	2863	congruent melting: CaO liquid: O 0.5; CaO: O 0.5	experimental	[2] Liang 2018 cites Noguchi 1967 doi	Table 2, p. 5, row 6 report
Phase composition	2886	congruent melting: CaO liquid: O 0.5; CaO: O 0.5	model	[2] Liang 2018 cites Hlavac 1982 doi	Table 2, p. 5, row 12 report
Phase composition	2886	congruent melting: CaO liquid: O 0.5; CaO: O 0.5	model	[2] Liang 2018 cites Wriedt 1985 doi	Table 2, p. 5, row 13 report
Phase composition	2890	congruent melting: CaO liquid: O 0.5; CaO: O 0.5	experimental	[2] Liang 2018 cites Panek 1979	Table 2, p. 5, row 9 report
Phase composition	2893	congruent melting: CaO liquid: O 0.5; CaO: O 0.5	experimental	[2] Liang 2018 cites OlShanskil 1958	Table 2, p. 5, row 3 report
Phase composition	2898	congruent melting: CaO liquid: O 0.5; CaO: O 0.5	experimental	[2] Liang 2018 cites Doman 1963	Table 2, p. 5, row 4 report
Phase composition	2900	congruent melting: CaO liquid: O 0.5; CaO: O 0.5	model	[2] Liang 2018 cites Kubaschewski 1993	Table 2, p. 5, row 14 report
Phase composition	3172	congruent melting: CaO liquid: O 0.5; CaO: O 0.5	experimental	[2] Liang 2018 cites Yamada 1986 doi	Table 2, p. 5, row 10 report
Phase composition	3172	congruent melting: CaO liquid: O 0.5; CaO: O 0.5	model	[2] Liang 2018 cites SGTE 2013	Table 2, p. 5, row 17 report
Phase composition	3173	congruent melting: CaO liquid: O 0.5; CaO: O 0.5	experimental	[2] Liang 2018 cites Traverse 1969	Table 2, p. 5, row 8 report
Phase composition	3183	congruent melting: CaO liquid: O 0.5; CaO: O 0.5	experimental	[2] Liang 2018 cites Foex 1965 doi	Table 2, p. 5, row 5 report
Phase composition	3200	congruent melting: CaO liquid: O 0.5; CaO: O 0.5	model	[2] Liang 2018 cites Chase 1998	Table 2, p. 5, row 15 report
Phase composition	3222	congruent melting: CaO liquid: O 0.5; CaO: O 0.5	model	[2] Liang 2018	Table 2, p. 5, row 18 report
Phase composition	3222	congruent melting: CaO liquid: O 0.5; CaO: O 0.5	experimental	[2] Liang 2018 cites Manara 2014	Table 2, p. 5, row 11 report
Phase composition	3223	congruent melting: CaO liquid: O 0.5; CaO: O 0.5	experimental	[2] Liang 2018 cites Foex 1968	Table 2, p. 5, row 7 report

Heat capacity / entropy / enthalpy (26)

Heat capacity / entropy / enthalpy, Ca–O system
Property	Value	T (K)	Phases / composition	Class	Source	Location
Entropy printed: S°	19.105 J/mol-atom/K	298.15	CaO(cr) alloy: O 0.5	model	[1] Deffrennes 2020 cites Chase 1998	Table 3, p. 17, row 6 report
Entropy printed: S°	19.05 J/mol-atom/K	298.15	CaO(cr) alloy: O 0.5	model	[1] Deffrennes 2020 cites Liang 2018 doi	Table 3, p. 17, row 2 report
Entropy printed: S°	20.175 J/mol-atom/K	298.15	CaO(cr) alloy: O 0.5	model	[1] Deffrennes 2020	Table 3, p. 17, row 1 report
Entropy printed: S°	20.175 J/mol-atom/K	298.15	CaO(cr) alloy: O 0.5	DFT	[1] Deffrennes 2020 cites Pisch	Table 3, p. 17, row 5 report
Entropy printed: S°	18.875 J/mol-atom/K	298.15	CaO(cr) alloy: O 0.5	model	[1] Deffrennes 2020 cites Lindberg 2009 doi	Table 3, p. 17, row 3 report
Entropy printed: S°	31.16 J/mol-atom/K	298.15	CaO(liq-am) alloy: O 0.5	model	[1] Deffrennes 2020 cites Chase 1998	Table 3, p. 17, row 10 report
Entropy printed: S°	29.345 J/mol-atom/K	298.15	CaO(liq-am) alloy: O 0.5	model	[1] Deffrennes 2020 cites Liang 2018 doi	Table 3, p. 17, row 8 report
Entropy printed: S°	20.175 J/mol-atom/K	298.15	CaO(liq-am) alloy: O 0.5	model	[1] Deffrennes 2020	Table 3, p. 17, row 7 report
Entropy printed: S°	32.845 J/mol-atom/K	298.15	CaO(liq-am) alloy: O 0.5	model	[1] Deffrennes 2020 cites Lindberg 2009 doi	Table 3, p. 17, row 9 report
Entropy printed: S°	27.8933 J/mol-atom/K	298.15	CaO2(cr) alloy: O 0.666667	model	[1] Deffrennes 2020 cites Lindberg 2009 doi	Table 3, p. 17, row 13 report
Entropy printed: S°	19.8667 J/mol-atom/K	298.15	CaO2(cr) alloy: O 0.666667	DFT	[1] Deffrennes 2020 cites Pisch	Table 3, p. 17, row 14 report
Entropy printed: S°	19.8667 J/mol-atom/K	298.15	CaO2(cr) alloy: O 0.666667	model	[1] Deffrennes 2020	Table 3, p. 17, row 11 report
Entropy printed: S°	27.8933 J/mol-atom/K	298.15	CaO2(cr) alloy: O 0.666667	model	[1] Deffrennes 2020 cites Liang 2018 doi	Table 3, p. 17, row 12 report
Heat capacity printed: Cp°	21.06 J/mol-atom/K	298.15	CaO(cr) alloy: O 0.5	model	[1] Deffrennes 2020 cites Chase 1998	Table 3, p. 17, row 6 report
Heat capacity printed: Cp°	21.025 J/mol-atom/K	298.15	CaO(cr) alloy: O 0.5	model	[1] Deffrennes 2020 cites Liang 2018 doi	Table 3, p. 17, row 2 report
Heat capacity printed: Cp°	21.365 J/mol-atom/K	298.15	CaO(cr) alloy: O 0.5	model	[1] Deffrennes 2020	Table 3, p. 17, row 1 report
Heat capacity printed: Cp°	21.365 J/mol-atom/K	298.15	CaO(cr) alloy: O 0.5	DFT	[1] Deffrennes 2020 cites Pisch	Table 3, p. 17, row 5 report
Heat capacity printed: Cp°	21.01 J/mol-atom/K	298.15	CaO(cr) alloy: O 0.5	model	[1] Deffrennes 2020 cites Lindberg 2009 doi	Table 3, p. 17, row 3 report
Heat capacity printed: Cp°	21.06 J/mol-atom/K	298.15	CaO(liq-am) alloy: O 0.5	model	[1] Deffrennes 2020 cites Chase 1998	Table 3, p. 17, row 10 report
Heat capacity printed: Cp°	21.02 J/mol-atom/K	298.15	CaO(liq-am) alloy: O 0.5	model	[1] Deffrennes 2020 cites Liang 2018 doi	Table 3, p. 17, row 8 report
Heat capacity printed: Cp°	21.365 J/mol-atom/K	298.15	CaO(liq-am) alloy: O 0.5	model	[1] Deffrennes 2020	Table 3, p. 17, row 7 report
Heat capacity printed: Cp°	21.01 J/mol-atom/K	298.15	CaO(liq-am) alloy: O 0.5	model	[1] Deffrennes 2020 cites Lindberg 2009 doi	Table 3, p. 17, row 9 report
Heat capacity printed: Cp°	27.6133 J/mol-atom/K	298.15	CaO2(cr) alloy: O 0.666667	model	[1] Deffrennes 2020 cites Lindberg 2009 doi	Table 3, p. 17, row 13 report
Heat capacity printed: Cp°	20.5267 J/mol-atom/K	298.15	CaO2(cr) alloy: O 0.666667	DFT	[1] Deffrennes 2020 cites Pisch	Table 3, p. 17, row 14 report
Heat capacity printed: Cp°	20.5433 J/mol-atom/K	298.15	CaO2(cr) alloy: O 0.666667	model	[1] Deffrennes 2020	Table 3, p. 17, row 11 report
Heat capacity printed: Cp°	27.6133 J/mol-atom/K	298.15	CaO2(cr) alloy: O 0.666667	model	[1] Deffrennes 2020 cites Liang 2018 doi	Table 3, p. 17, row 12 report

Sources

Reporting papers the values were read from (a value cited from another work names that work in its row).

Guillaume Deffrennes, Noël Jakse, Cecilia M.S. Alvares, Ioana Nuta, Alain Pasturel, Alexandra Khvan et al., Thermodynamic modelling of the Ca–O system including 3rd generation description of CaO and CaO2, Calphad 69, 101764 (2020). doi:10.1016/j.calphad.2020.101764
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). doi:10.1016/j.jeurceramsoc.2018.06.015

Please cite

R. Arróyave, J. Saal, D. Shin, ORCHID-Values: thermodynamic and phase-equilibrium values read from the literature (version 2026.10; Version 1, machine-extracted), Zenodo (2026). doi:10.5281/zenodo.23735569
R. Arróyave, J. Saal, D. Shin, ORCHID-Diagrams: calculated binary phase diagrams (version 2026.10), Zenodo (2026). doi:10.5281/zenodo.23735859
R. Arróyave, J. Saal, D. Shin, ORCHID-Hulls: binary convex hulls (Materials Project, OQMD, assessed CALPHAD) (version 2026.10), Zenodo (2026). doi:10.5281/zenodo.23735891
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 the original source of every value you use (paper_citation / paper_doi, and cited_dois for values the paper cites from earlier work); 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). 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_literature_2026,
  author    = {Arr{\'o}yave, Raymundo and Saal, James and Shin, Dongwon},
  title     = {{ORCHID-Values: thermodynamic and phase-equilibrium values read from the literature}},
  version   = {2026.10},
  publisher = {Zenodo},
  year      = {2026},
  doi       = {10.5281/zenodo.23735569},
  url       = {https://doi.org/10.5281/zenodo.23735569},
  note      = {Version 1, machine-extracted}
}

@misc{orchid_phase_diagrams_2026,
  author    = {Arr{\'o}yave, Raymundo and Saal, James and Shin, Dongwon},
  title     = {{ORCHID-Diagrams: calculated binary phase diagrams}},
  version   = {2026.10},
  publisher = {Zenodo},
  year      = {2026},
  doi       = {10.5281/zenodo.23735859},
  url       = {https://doi.org/10.5281/zenodo.23735859}
}

@misc{orchid_hulls_2026,
  author    = {Arr{\'o}yave, Raymundo and Saal, James and Shin, Dongwon},
  title     = {{ORCHID-Hulls: binary convex hulls (Materials Project, OQMD, assessed CALPHAD)}},
  version   = {2026.10},
  publisher = {Zenodo},
  year      = {2026},
  doi       = {10.5281/zenodo.23735891},
  url       = {https://doi.org/10.5281/zenodo.23735891}
}

@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}
}