Na–O system

53 accepted literature values from 1 paper(s) (experimental 14, model 13, unspecified 26); 1 calculated phase diagram(s). 10 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 (12) · papers (bibliography) · Markdown

Accepted values by evidence class
Evidence class	Values
experimental	14
model	13
unspecified	26

Accepted values by property group
Property group	Values
invariant reaction	21
phase transition	10
formation	1
heat capacity / entropy / enthalpy	6
crystal structure	14
other property	1

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
NaO-17Smi.tdb	A.L. Smith, C. Gueneau, J.-L. Fleche, S. Chatain, O. Benes, R.J.M. Konings, J. Chem. Thermodyn., 114, 93-115(2017). doi:10.1016/j.jct.2017.04.003	`4ebf441b547a4b2895515dae79c20e93c2cb5463d45a8fa87793a6baeea0f7b5`	viewer · TDB · JSON

Convex hulls: Materials Project DFT hull · OQMD DFT hull

Invariant reactions (literature)

Invariant reactions reported in the literature for the Na–O system (21)
T (K)	Reaction / phases	Compositions (mole fraction)	Class	Source	Location	Quote
1405.2	congruent melting: Na2O-III = L2		unspecified	[1] Smith 2017 cites Chase 1998	Table 7, p. 11, row 8 report
1403	congruent melting: Na2O-III = L2		model	[1] Smith 2017	Table 7, p. 11, row 7 report
1403	monotectic: Na2O-III + L1 = L2	L1: O 0.047	experimental	[1] Smith 2017 cites Wriedt 1987 doi	Table 7, p. 11, row 16 report
1402	monotectic: Na2O-III + L1 = L2	L1: O 0.047; L2: O 0.333	model	[1] Smith 2017	Table 7, p. 11, row 15 report
1243.2	polymorphic: Na2O-II = Na2O-III		unspecified	[1] Smith 2017 cites Chase 1998	Table 7, p. 11, row 6 report
1241	polymorphic: Na2O-II = Na2O-III		model	[1] Smith 2017	Table 7, p. 11, row 5 report
1023.2	polymorphic: Na2O-I = Na2O-II		unspecified	[1] Smith 2017 cites Chase 1998	Table 7, p. 11, row 4 report
1020.3	polymorphic: Na2O-I = Na2O-II		model	[1] Smith 2017	Table 7, p. 11, row 3 report
948	congruent melting: Na2O2-II = L2		unspecified	[1] Smith 2017 cites Chase 1998	Table 7, p. 11, row 12 report
948	congruent melting: Na2O2-II = L2		model	[1] Smith 2017	Table 7, p. 11, row 11 report
843	eutectic: Na2O-I + Na2O2-II = liquid		model	[1] Smith 2017	p. 7 report	The eutectic equilibrium Na2O-I + Na2O2-II = liquid at 843 K was never observed experimentally.
843	eutectic: Na2O-I + Na2O2-II = liquid		model	[1] Smith 2017 cites Wriedt 1987 doi	p. 21 report	The present DSC measurements moreover argue for the existence of a {Na2O-I + Na2O2-II = liquid} eutectic equilibrium at 843 K as anticipated by Wriedt [14].
843	eutectic: Na2O-I + Na2O2-II = L2	L2: O 0.44	experimental	[1] Smith 2017 cites Bunzel 1947	Table 7, p. 11, row 20 report
826	congruent melting: NaO2-I = L2		model	[1] Smith 2017	Table 7, p. 11, row 13 report
825	congruent melting: NaO2-I = L2		unspecified	[1] Smith 2017 cites Chase 1998	Table 7, p. 11, row 14 report
785	polymorphic: Na2O2-I = Na2O2-II		unspecified	[1] Smith 2017 cites Chase 1998	Table 7, p. 11, row 10 report
782	polymorphic: Na2O2-I = Na2O2-II		model	[1] Smith 2017	Table 7, p. 11, row 9 report
371	eutectic: β-Na + Na2O-I = L1		experimental	[1] Smith 2017 cites Wriedt 1987 doi	Table 7, p. 11, row 18 report
370.98	congruent melting: β-Na = L1		model	[1] Smith 2017	Table 7, p. 11, row 1 report
370.98	congruent melting: β-Na = L1		unspecified	[1] Smith 2017 cites Chase 1998	Table 7, p. 11, row 2 report
370.98	eutectic: β-Na + Na2O-I = L1		model	[1] Smith 2017	Table 7, p. 11, row 17 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, Na–O system (1)
Phase	Compound	Value	T (K)	Class	MP DFT (kJ/mol-atom)	OQMD DFT (kJ/mol-atom)	Source	Location	Quote
NaO3(cr)		-188 kJ/mol (basis unstated)	298.15	unspecified			[1] Smith 2017 cites Wriedt 1987 doi	Table 2, p. 4, row 15 report

Other properties

Phase transition (10)

Phase transition, Na–O system
Property	Value	T (K)	Phases / composition	Class	Source	Location
Phase transition	756.8 K	756.8	polymorphic alloy: Na 0.5, O 0.5	experimental	[1] Smith 2017	Table 5, p. 6, row 1 report
Phase transition	765.8 K	765.8	polymorphic: Na2O2-I = Na2O2-II alloy: Na 0.5263, O 0.4737	experimental	[1] Smith 2017	Table 5, p. 6, row 3 report
Phase transition	819.7 K	819.7	eutectic: L2 = Na2O-I + Na2O2-II alloy: Na 0.625, O 0.375	experimental	[1] Smith 2017	Table 5, p. 6, row 10 report
Phase transition	821.2 K	821.2	eutectic: L2 = Na2O-I + Na2O2-II alloy: Na 0.5714, O 0.4286	experimental	[1] Smith 2017	Table 5, p. 6, row 8 report
Phase transition	832.6 K	832.6	eutectic: L2 = Na2O-I + Na2O2-II alloy: Na 0.5406, O 0.4594	experimental	[1] Smith 2017	Table 5, p. 6, row 6 report
Phase transition	863.5 K	863.5	eutectic: L2 = Na2O-I + Na2O2-II alloy: Na 0.5263, O 0.4737	experimental	[1] Smith 2017	Table 5, p. 6, row 4 report
Phase transition	939.8 K	939.8	congruent transformation: Na2O2-II = L2 alloy: Na 0.5, O 0.5	experimental	[1] Smith 2017	Table 5, p. 6, row 2 report
Phase transition	991.6 K	991.6	polymorphic: Na2O-I = Na2O-II alloy: Na 0.5406, O 0.4594	experimental	[1] Smith 2017	Table 5, p. 6, row 5 report
Phase transition	1025.5 K	1025.5	polymorphic: Na2O-I = Na2O-II alloy: Na 0.625, O 0.375	experimental	[1] Smith 2017	Table 5, p. 6, row 9 report
Phase transition	1042.8 K	1042.8	polymorphic: Na2O-I = Na2O-II alloy: Na 0.5714, O 0.4286	experimental	[1] Smith 2017	Table 5, p. 6, row 7 report

Heat capacity / entropy / enthalpy (6)

Heat capacity / entropy / enthalpy, Na–O system
Property	Value	T (K)	Phases / composition	Class	Source	Location
Entropy printed: S°m(298.15 K)	75.04 J/mol (basis unstated)/K ± 0.1	298.15	Na2O-I(cr) alloy: O 0.333333	unspecified	[1] Smith 2017 cites Chase 1998	Table 2, p. 4, row 5 report
Entropy printed: S°m(298.15 K)	75.04 J/mol (basis unstated)/K ± 0.1	298.15	Na2O-I(cr) alloy: O 0.333333	unspecified	[1] Smith 2017	Table 2, p. 4, row 17 report
Entropy printed: S°m(298.15 K)	94.809 J/mol (basis unstated)/K ± 1.3	298.15	Na2O2-I(cr) alloy: O 0.5	unspecified	[1] Smith 2017 cites Chase 1998	Table 2, p. 4, row 10 report
Entropy printed: S°m(298.15 K)	94.809 J/mol (basis unstated)/K ± 1.3	298.15	Na2O2-I(cr) alloy: O 0.5	unspecified	[1] Smith 2017	Table 2, p. 4, row 18 report
Entropy printed: S°m(298.15 K)	115.9 J/mol (basis unstated)/K ± 1.3	298.15	NaO2-I(cr) alloy: O 0.666667	unspecified	[1] Smith 2017 cites Chase 1998	Table 2, p. 4, row 14 report
Entropy printed: S°m(298.15 K)	115.9 J/mol (basis unstated)/K ± 1.3	298.15	NaO2-I(cr) alloy: O 0.666667	unspecified	[1] Smith 2017	Table 2, p. 4, row 19 report

Crystal structure (14)

Crystal structure, Na–O system
Property	Value	T (K)	Phases / composition	Class	Source	Location
Lattice a	4.335 Å	4	NaO2-IV alloy: O 0.666667	unspecified	[1] Smith 2017 cites Wriedt 1987 doi	Table 1, p. 3, row 7 report
Lattice a	4.26 Å	173	NaO2-III alloy: O 0.666667	unspecified	[1] Smith 2017 cites Wriedt 1987 doi	Table 1, p. 3, row 8 report
Lattice a	5.46 Å ± 0.01	203	NaO2-II alloy: O 0.666667	unspecified	[1] Smith 2017 cites Wriedt 1987 doi	Table 1, p. 3, row 9 report
Lattice a	3.507 Å ± 2.000e-4	213	NaO3 alloy: O 0.75	unspecified	[1] Smith 2017 cites Klein 1998 doi	Table 1, p. 3, row 11 report
Lattice a	5.512 Å ± 0.02	293	NaO2-I alloy: O 0.666667	unspecified	[1] Smith 2017 cites Wriedt 1987 doi	Table 1, p. 3, row 10 report
Lattice a	5.55 Å	295	Na2O-I alloy: O 0.333333	unspecified	[1] Smith 2017 cites Wriedt 1987 doi	Table 1, p. 3, row 2 report
Lattice a	6.207 Å ± 0.004	295	Na2O2-I alloy: O 0.5	model	[1] Smith 2017 cites Wriedt 1987 doi	Table 1, p. 3, row 5 report
Lattice b	5.537 Å	4	NaO2-IV alloy: O 0.666667	unspecified	[1] Smith 2017 cites Wriedt 1987 doi	Table 1, p. 3, row 7 report
Lattice b	5.54 Å	173	NaO2-III alloy: O 0.666667	unspecified	[1] Smith 2017 cites Wriedt 1987 doi	Table 1, p. 3, row 8 report
Lattice b	5.7703 Å ± 3.000e-4	213	NaO3 alloy: O 0.75	unspecified	[1] Smith 2017 cites Klein 1998 doi	Table 1, p. 3, row 11 report
Lattice c	3.363 Å	4	NaO2-IV alloy: O 0.666667	unspecified	[1] Smith 2017 cites Wriedt 1987 doi	Table 1, p. 3, row 7 report
Lattice c	3.44 Å	173	NaO2-III alloy: O 0.666667	unspecified	[1] Smith 2017 cites Wriedt 1987 doi	Table 1, p. 3, row 8 report
Lattice c	5.2708 Å ± 3.000e-4	213	NaO3 alloy: O 0.75	unspecified	[1] Smith 2017 cites Klein 1998 doi	Table 1, p. 3, row 11 report
Lattice c	4.471 Å ± 0.003	295	Na2O2-I alloy: O 0.5	model	[1] Smith 2017 cites Wriedt 1987 doi	Table 1, p. 3, row 5 report

Other property (1)

Other property, Na–O system
Property	Value	T (K)	Phases / composition	Class	Source	Location	Quote
Other printed: Dtr Hom	25.4 kJ mol 1	1193		experimental	[1] Smith 2017 cites Cordfunke 1995 doi	p. 10 report	The transition enthalpy for Na2UO4 was reported as Dtr Hom ðNa2 UO4 ; cr; 1193KÞ = 25.4 kJmol1, based on the differential thermal analysis (DTA) measurements by Cordfunke and IJdo [71] and enthalpy increment measurements by Fredrickson and O'Hare using drop calorimetry [82].

Sources

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

A.L. Smith, C. Guéneau, J.-L. Flèche, S. Chatain, O. Beneš, R.J.M. Konings, Thermodynamic assessment of the Na-O and Na-U-O systems: Margin to the safe operation of SFRs, The Journal of Chemical Thermodynamics 114, 93-115 (2017). doi:10.1016/j.jct.2017.04.003

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}
}