Ba–O system

36 accepted literature values from 2 paper(s) (experimental 17, model 19); 1 calculated phase diagram(s). 43 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 (10) · papers (bibliography) · Markdown

Accepted values by evidence class
Evidence class	Values
experimental	17
model	19

Accepted values by property group
Property group	Values
invariant reaction	4
phase transition	6
formation	14
heat capacity / entropy / enthalpy	12

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
BaO-95Zim.tdb	E. Zimmermann, K. Hack, D. Neuschutz, Calphad, 19, 119-27(1995). doi:10.1016/0364-5916(95)00012-4	`a0f7658f38a4a7d7eb4fba12550e7fb56477c73cbf19cc89076a0a1247457773`	viewer · TDB · JSON

Calculated three-phase invariants (model, mole fraction of the second component)
TDB file	T (K)	Phases at the invariant
BaO-95Zim.tdb	1962.85	BAO (x(O) 0.50109) + LIQUID (x(O) 0.56843) + GAS (x(O) 0.99993)
BaO-95Zim.tdb	1096.02	BAO#2 (x(O) 0.5158) + BAO (x(O) 0.61991) + GAS (x(O) 1)
BaO-95Zim.tdb	1096.02	BAO (x(O) 0.5158) + BAO#2 (x(O) 0.61991) + O2GAS (x(O) 1)
BaO-95Zim.tdb	854.47	BCC_A2 (x(O) 0) + LIQUID (x(O) 0.09782) + BAO (x(O) 0.5)

Convex hulls: Materials Project DFT hull · OQMD DFT hull

Invariant reactions (literature)

Invariant reactions reported in the literature for the Ba–O system (4)
T (K)	Reaction / phases	Compositions (mole fraction)	Class	Source	Location
1630	eutectic: Liquid -> BaO + gas	L: O 0.575; BaO: O 0.506; gas: O 1	model	[1] Zhou 2005	Table III, p. 6, row 4 report
1096	peritectic: BaO + gas -> BaO2	BaO: O 0.509; gas: O 1; BaO2: O 0.618	model	[1] Zhou 2005	Table III, p. 6, row 6 report
1096	peritectic: BaO + gas -> BaO2	BaO: O 0.509; gas: O 1; BaO2: O 0.624	model	[1] Zhou 2005	Table III, p. 6, row 5 report
842	eutectic: Liquid -> bcc + BaO	L: O 0.1; bcc: O 0; BaO: O 0.5	model	[1] Zhou 2005	Table III, p. 6, row 7 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, Ba–O system (14)
Phase	Compound	Value	T (K)	Class	MP DFT (kJ/mol-atom)	OQMD DFT (kJ/mol-atom)	Source	Location
Ba2O2(G)		-125.9 kJ/mol-atom	298.15	model			[2] Zimmermann 1995	Table 2, p. 5, row 9 report
Ba2O3(G)		-100.72 kJ/mol-atom	298.15	model			[2] Zimmermann 1995	Table 2, p. 5, row 9 report
BaO		-274.03 kJ/mol (basis unstated)	298.15	experimental			[1] Zhou 2005 cites Hedvall 1918	Table I, p. 3, row 2 report
BaO(G)		-60.45 kJ/mol-atom	298.15	model			[2] Zimmermann 1995	Table 2, p. 5, row 6 report
BaO(L)		-250.138 kJ/mol-atom	298.15	model			[2] Zimmermann 1995	Table 2, p. 5, row 3 report
BaO(S)	BaO	-276.68 kJ/mol-atom	298.15	model	-272.439 (mp-aaaaabzq)	-259.209 (oqmd-1343705)	[2] Zimmermann 1995	Table 2, p. 5, row 1 report
BaO2(S)	BaO2	-211.9 kJ/mol-atom	298.15	model	-209.391 (mp-aaaaabqn)	-205.059 (oqmd-1984787)	[2] Zimmermann 1995	Table 2, p. 5, row 5 report
BaO^s		-581.83 kJ/mol (basis unstated)	298.15	experimental			[2] Zimmermann 1995 cites ref. 52Mah	Table 1, p. 3, row 4 report
BaO^s		-560.82 kJ/mol (basis unstated)	298.15	experimental			[2] Zimmermann 1995 cites ref. 23Gun	Table 1, p. 3, row 2 report
BaO^s		-556.47 kJ/mol (basis unstated)	298.15	experimental			[2] Zimmermann 1995 cites ref. 56Zai	Table 1, p. 3, row 3 report
BaO^s		-552.71 kJ/mol (basis unstated)	298.15	experimental			[2] Zimmermann 1995 cites ref. 66Fli	Table 1, p. 3, row 5 report
BaO^s		-548.02 kJ/mol (basis unstated)	298.15	experimental			[2] Zimmermann 1995 cites ref. 73Fit	Table 1, p. 3, row 6 report
BaO^s		-548.02 kJ/mol (basis unstated)	298.15	experimental			[2] Zimmermann 1995 cites ref. 90Cor	Table 1, p. 3, row 7 report
BaO^s		-526.5 kJ/mol (basis unstated)	298.15	experimental			[2] Zimmermann 1995 cites ref. 08For	Table 1, p. 3, row 1 report

Other properties

Phase transition (6)

Phase transition, Ba–O system
Property	Value	T (K)	Phases / composition	Class	Source	Location	Quote
Phase transition	2197 K	2197	liquid	experimental	[1] Zhou 2005 cites Schriel 1937	p. 1 report	For example, Glushko,18 Moissan,19 Foex20 and Schumacher21 measured melting temperatures of 2290, 2273, 2286, and 2197 K, respectively.
Phase transition	2273 K	2273	liquid	experimental	[1] Zhou 2005 cites Foex 1965	p. 1 report	For example, Glushko,18 Moissan,19 Foex20 and Schumacher21 measured melting temperatures of 2290, 2273, 2286, and 2197 K, respectively.
Phase transition	2286 K	2286	liquid	experimental	[1] Zhou 2005 cites Schumacher 1926	p. 1 report	For example, Glushko,18 Moissan,19 Foex20 and Schumacher21 measured melting temperatures of 2290, 2273, 2286, and 2197 K, respectively.
Phase transition	2287 K	2287	congruent melting: Liquid -> BaO L: O 0.5; BaO: O 0.5	model	[1] Zhou 2005	Table III, p. 6, row 2 report
Phase transition	2290 K	2290	liquid	experimental	[1] Zhou 2005 cites Moissan 1902	p. 1 report	For example, Glushko,18 Moissan,19 Foex20 and Schumacher21 measured melting temperatures of 2290, 2273, 2286, and 2197 K, respectively.
Phase transition	3249 K	3249	congruent melting: Gas -> liquid Gas: O 0.539; L: O 0.539	model	[1] Zhou 2005	Table III, p. 6, row 1 report

Heat capacity / entropy / enthalpy (12)

Heat capacity / entropy / enthalpy, Ba–O system
Property	Value	T (K)	Phases / composition	Class	Source	Location	Quote
Entropy printed: entropy	35.01 J/K/mole of atoms	298.15		experimental	[1] Zhou 2005 cites Cordfunke 1994	p. 3 report	Its heat capacity, as measured by different authors 32,33,34 using an adiabatic calorimeter, was plotted in Fig. 2, and was used to calculate the entropy32 at 298K to be 35.01 J/K/mole of atoms.
Entropy printed: entropy	29.18 J/K/mole of atoms	298.15		experimental	[1] Zhou 2005 cites Gavrichev	p. 3 report	The heat capacity of the BaO2 phase was measured by Gavrichev et al.35 by means of a calorimeter (see Fig. 2) and was used to calculate its entropy35 as 29.18 J/K/mole of atoms at 298K.
Entropy printed: S298	89.475 J/mol-atom/K	298.15	Ba2O2(G) alloy: O 0.5	model	[2] Zimmermann 1995	Table 2, p. 5, row 9 report
Entropy printed: S298	71.58 J/mol-atom/K	298.15	Ba2O3(G) alloy: O 0.5	model	[2] Zimmermann 1995	Table 2, p. 5, row 9 report
Entropy printed: Entropy of formation at 298 K	34.99 J/mol (basis unstated)/K	298.15	BaO alloy: O 0.5	model	[1] Zhou 2005	Table I, p. 3, row 10 report
Entropy printed: Entropy of formation at 298 K	35.01 J/mol (basis unstated)/K	298.15	BaO alloy: O 0.5	experimental	[1] Zhou 2005 cites Zaitseva 1956	Table I, p. 3, row 3 report
Entropy printed: Entropy of formation	35.01 J/mol (basis unstated)/K	298.15	BaO alloy: O 0.5	experimental	[1] Zhou 2005 cites Hedvall 1918	Table I, p. 3, row 2 report
Entropy printed: S298	117.73 J/mol-atom/K	298.15	BaO(G) alloy: O 0.5	model	[2] Zimmermann 1995	Table 2, p. 5, row 6 report
Entropy printed: S298	47.438 J/mol-atom/K	298.15	BaO(L) alloy: O 0.5	model	[2] Zimmermann 1995	Table 2, p. 5, row 3 report
Entropy printed: S298	36.035 J/mol-atom/K	298.15	BaO(S) alloy: O 0.5	model	[2] Zimmermann 1995	Table 2, p. 5, row 1 report
Entropy printed: Entropy of formation	29.18 J/mol (basis unstated)/K	298.15	BaO2 alloy: O 0.666667	experimental	[1] Zhou 2005	Table I, p. 3, row 8 report
Entropy printed: S298	30.9167 J/mol-atom/K	298.15	BaO2(S) alloy: O 0.666667	model	[2] Zimmermann 1995	Table 2, p. 5, row 5 report

Sources

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

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). doi:10.1111/j.1551-2916.2005.00368.x
E. Zimmermann, K. Hack, D. Neuschütz, Thermochemical assessment of the binary system Ba-O, Calphad 19, 119-127 (1995). doi:10.1016/0364-5916(95)00012-4

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}
}