Nb–O phases

10 phases (tier A 3, tier B 1, tier C 2, liquid 2, gas 2); 7 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 · Nb–O system page · Markdown · field reference

Phases of the Nb–O system (10)
Phase	Structure	Basis	Stability (calculated)	Literature values	TDB models
BCC_A2 phase:nb-o:bcc-a2	W · A2 · cI2 · Im-3m (229)	tier A: standard phase name	stable in 2 of 2 calculated diagram(s): 300–2749.99 K, x(O) 0–0.09041	0	2
FCC_A1 phase:nb-o:fcc-a1	Cu · A1 · cF4 · Fm-3m (225)	tier A: standard phase name	not stable in 2 calculated diagram(s)	0	2
GAS phase:nb-o:gas	gas	gas	stable in 2 of 2 calculated diagram(s): 301.19–4000 K, x(O) 0.67471–1	0	2
HCP_A3 phase:nb-o:hcp-a3	Mg · A3 · hP2 · P6_3/mmc (194)	tier A: standard phase name	not stable in 2 calculated diagram(s)	0	2
ION phase:nb-o:ion	liquid	liquid	stable in 2 of 2 calculated diagram(s): 1782.33–4000 K, x(O) 1e-05–0.71423	0	2
LIQUID phase:nb-o:liquid	liquid	liquid	not stable in 2 calculated diagram(s)	0	2
NB2O5 phase:nb-o:nb2o5	Nb2O5 · mP99 · P2/m (10)	tier C: assessor-stated (Hallstedt 2025 crystallographic table)	stable in 2 of 2 calculated diagram(s): 300–1966.19 K, x(O) 0.71429–0.71429	0	2
NBO phase:nb-o:nbo	NbO · cP6 · Pm-3m (221)	tier B: DFT-supported (unique MP + OQMD match)	stable in 2 of 2 calculated diagram(s): 300–2218.25 K, x(O) 0.5–0.5	0	2
NBO2 phase:nb-o:nbo2	NbO2 · tI96 · I4_1/a (88)	tier C: assessor-stated (Hallstedt 2025 crystallographic table)	stable in 2 of 2 calculated diagram(s): 300–2181.28 K, x(O) 0.66667–0.66667	1	2
O2GAS phase:nb-o:o2gas	gas	gas	stable in 2 of 2 calculated diagram(s): 300–1185 K, x(O) 1–1	0	2

BCC_A2 (Nb–O)

Id: phase:nb-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: stable in 2 of 2 calculated diagram(s): 300–2749.99 K, x(O) 0–0.09041
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (3): corpus: corpus:phase:nb-o:bcc-a2
tdb: tdb:NbO-07Jer.tdb:BCC_A2, tdb:NbO-97Dup-LB.tdb:BCC_A2

TDB models of BCC_A2 (2): PHASE and CONSTITUENT statements as written

NbO-07Jer.tdb: BCC_A2, type code %B, sha256 30d68ef18e1752dc…

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

NbO-97Dup-LB.tdb: BCC_A2, type code %B, sha256 7461691cb95cdbdf…

50: PHASE BCC_A2 %B 2 1 3 !
51: CONST BCC_A2 : NB : O VA : !

Example references (1 of 1; assessments first):

doi:10.1016/j.jnucmat.2006.10.008 R. Jerlerud Pérez, A.R. Massih, Thermodynamic evaluation of the Nb–O–Zr system, Journal of Nuclear Materials 360, 242-254 (2007).
assessment that models this phase

FCC_A1 (Nb–O)

Id: phase:nb-o:fcc-a1; status assigned
Structure: Cu · A1 · cF4 · Fm-3m (225); type st:a1-cu-cf4; tier A: standard phase name; confidence high
Stoichiometry: Nb 1.0000
Stability: not stable in 2 calculated diagram(s)
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (3): corpus: corpus:phase:nb-o:fcc-a1
tdb: tdb:NbO-07Jer.tdb:FCC_A1, tdb:NbO-97Dup-LB.tdb:FCC_A1

TDB models of FCC_A1 (2): PHASE and CONSTITUENT statements as written

NbO-07Jer.tdb: FCC_A1, type code %A, sha256 30d68ef18e1752dc…

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

NbO-97Dup-LB.tdb: FCC_A1, type code %A, sha256 7461691cb95cdbdf…

45: PHASE FCC_A1 %A 2 1 1 !
46: CONST FCC_A1 : NB : VA : !

Example references (1 of 1; assessments first):

doi:10.1016/j.jnucmat.2006.10.008 R. Jerlerud Pérez, A.R. Massih, Thermodynamic evaluation of the Nb–O–Zr system, Journal of Nuclear Materials 360, 242-254 (2007).
assessment that models this phase

GAS (Nb–O)

Id: phase:nb-o:gas; status assigned
Structure: gas; type st:gas; gas; confidence high
Stability: stable in 2 of 2 calculated diagram(s): 301.19–4000 K, x(O) 0.67471–1
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (3): corpus: corpus:phase:nb-o:gas
tdb: tdb:NbO-07Jer.tdb:GAS, tdb:NbO-97Dup-LB.tdb:GAS

TDB models of GAS (2): PHASE and CONSTITUENT statements as written

NbO-07Jer.tdb: GAS, type code %, sha256 30d68ef18e1752dc…

73: PHASE GAS:G % 1 1 !
74: CONST GAS:G : NB NBO NBO2 O O2 O3 : !

NbO-97Dup-LB.tdb: GAS, type code %, sha256 7461691cb95cdbdf…

76: PHASE GAS:G % 1 1 !
77: CONST GAS:G : NB NBO NBO2 O O2 O3 : !

Example references (1 of 1; assessments first):

doi:10.1016/j.jnucmat.2006.10.008 R. Jerlerud Pérez, A.R. Massih, Thermodynamic evaluation of the Nb–O–Zr system, Journal of Nuclear Materials 360, 242-254 (2007).
assessment that models this phase

HCP_A3 (Nb–O)

Id: phase:nb-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: not stable in 2 calculated diagram(s)
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (3): corpus: corpus:phase:nb-o:hcp-a3
tdb: tdb:NbO-07Jer.tdb:HCP_A3, tdb:NbO-97Dup-LB.tdb:HCP_A3

TDB models of HCP_A3 (2): PHASE and CONSTITUENT statements as written

NbO-07Jer.tdb: HCP_A3, type code %A, sha256 30d68ef18e1752dc…

52: PHASE HCP_A3 %A 2 1 1 !
53: CONST HCP_A3 : NB : O VA : !

NbO-97Dup-LB.tdb: HCP_A3, type code %A, sha256 7461691cb95cdbdf…

55: PHASE HCP_A3 %A 2 1 0.5 !
56: CONST HCP_A3 : NB : VA : !

Example references (1 of 1; assessments first):

doi:10.1016/j.jnucmat.2006.10.008 R. Jerlerud Pérez, A.R. Massih, Thermodynamic evaluation of the Nb–O–Zr system, Journal of Nuclear Materials 360, 242-254 (2007).
assessment that models this phase

ION (Nb–O)

Id: phase:nb-o:ion; status assigned
Structure: liquid; type st:liquid; liquid; confidence high
Stability: stable in 2 of 2 calculated diagram(s): 1782.33–4000 K, x(O) 1e-05–0.71423
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (3): corpus: corpus:phase:nb-o:ion
tdb: tdb:NbO-07Jer.tdb:ION, tdb:NbO-97Dup-LB.tdb:ION

TDB models of ION (2): PHASE and CONSTITUENT statements as written

NbO-07Jer.tdb: ION, type code %, sha256 30d68ef18e1752dc…

36: PHASE ION:Y % 2 1 1 !
37: CONST ION:Y : NB+2 : O-2 VA NBO2 NBO5/2 : !

NbO-97Dup-LB.tdb: ION, type code %, sha256 7461691cb95cdbdf…

40: PHASE ION:Y % 2 1 1 !
41: CONST ION:Y : NB+2 : O-2 VA NBO2 NBO5/2 : !

Example references (1 of 1; assessments first):

doi:10.1016/j.jnucmat.2006.10.008 R. Jerlerud Pérez, A.R. Massih, Thermodynamic evaluation of the Nb–O–Zr system, Journal of Nuclear Materials 360, 242-254 (2007).
assessment that models this phase

LIQUID (Nb–O)

Id: phase:nb-o:liquid; status assigned
Structure: liquid; type st:liquid; liquid; confidence high
Stoichiometry: Nb 1.0000
Stability: not stable in 2 calculated diagram(s)
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (3): corpus: corpus:phase:nb-o:liquid
tdb: tdb:NbO-07Jer.tdb:LIQUID, tdb:NbO-97Dup-LB.tdb:LIQUID

TDB models of LIQUID (2): PHASE and CONSTITUENT statements as written

NbO-07Jer.tdb: LIQUID, type code %, sha256 30d68ef18e1752dc…

33: PHASE LIQUID:L % 1 1 !
34: CONST LIQUID:L : NB : !

NbO-97Dup-LB.tdb: LIQUID, type code %, sha256 7461691cb95cdbdf…

37: PHASE LIQUID:L % 1 1 !
38: CONST LIQUID:L : NB : !

Example references (1 of 1; assessments first):

doi:10.1016/j.jnucmat.2006.10.008 R. Jerlerud Pérez, A.R. Massih, Thermodynamic evaluation of the Nb–O–Zr system, Journal of Nuclear Materials 360, 242-254 (2007).
assessment that models this phase

NB2O5 (Nb–O)

Id: phase:nb-o:nb2o5; status assigned
Structure: Nb2O5 · mP99 · P2/m (10); type st:nb2o5-mp99; 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 (mp_oqmd_space_groups_differ, no_structure_token); structure as stated in the SGTE crystallographic table for this phase name and system
Stoichiometry: Nb 0.2857, O 0.7143
Stability: stable in 2 of 2 calculated diagram(s): 300–1966.19 K, x(O) 0.71429–0.71429
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (3): corpus: corpus:phase:nb-o:nb2o5
tdb: tdb:NbO-07Jer.tdb:NB2O5, tdb:NbO-97Dup-LB.tdb:NB2O5

TDB models of NB2O5 (2): PHASE and CONSTITUENT statements as written

NbO-07Jer.tdb: NB2O5, type code %, sha256 30d68ef18e1752dc…

67: PHASE NB2O5 % 2 2 5 !
68: CONST NB2O5 : NB : O : !

NbO-97Dup-LB.tdb: NB2O5, type code %, sha256 7461691cb95cdbdf…

70: PHASE NB2O5 % 2 2 5 !
71: CONST NB2O5 : NB : O : !

Example references (1 of 1; assessments first):

doi:10.1016/j.jnucmat.2006.10.008 R. Jerlerud Pérez, A.R. Massih, Thermodynamic evaluation of the Nb–O–Zr system, Journal of Nuclear Materials 360, 242-254 (2007).
assessment that models this phase

NBO (Nb–O)

Id: phase:nb-o:nbo; status assigned
Structure: NbO · cP6 · Pm-3m (221); type st:nbo-cp6; tier B: DFT-supported (unique MP + OQMD match); confidence high
Stoichiometry: Nb 0.5000, O 0.5000
Stability: stable in 2 of 2 calculated diagram(s): 300–2218.25 K, x(O) 0.5–0.5
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (5): corpus: corpus:phase:nb-o:nbo
mp: mp:mp-aaaaadkx
oqmd: oqmd:oqmd-2921
tdb: tdb:NbO-07Jer.tdb:NBO, tdb:NbO-97Dup-LB.tdb:NBO

TDB models of NBO (2): PHASE and CONSTITUENT statements as written

NbO-07Jer.tdb: NBO, type code %, sha256 30d68ef18e1752dc…

57: PHASE NBO % 2 1 1 !
58: CONST NBO : NB : O : !

NbO-97Dup-LB.tdb: NBO, type code %, sha256 7461691cb95cdbdf…

60: PHASE NBO % 2 1 1 !
61: CONST NBO : NB : O : !

Example references (1 of 1; assessments first):

doi:10.1016/j.jnucmat.2006.10.008 R. Jerlerud Pérez, A.R. Massih, Thermodynamic evaluation of the Nb–O–Zr system, Journal of Nuclear Materials 360, 242-254 (2007).
assessment that models this phase

NBO2 (Nb–O)

Id: phase:nb-o:nbo2; status assigned
Structure: NbO2 · tI96 · I4_1/a (88); type st:nbo2-ti96; 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 (mp_oqmd_space_groups_differ, no_structure_token); structure as stated in the SGTE crystallographic table for this phase name and system
Stoichiometry: Nb 0.3333, O 0.6667
Stability: stable in 2 of 2 calculated diagram(s): 300–2181.28 K, x(O) 0.66667–0.66667
Literature: 1 values (1 accepted) from 1 papers
Interactive: phase registry entry

Names (4): corpus: corpus:phase:nb-o:nbo2
paper: paper:10.1016/j.jnucmat.2006.10.008:NbO2
tdb: tdb:NbO-07Jer.tdb:NBO2, tdb:NbO-97Dup-LB.tdb:NBO2

TDB models of NBO2 (2): PHASE and CONSTITUENT statements as written

NbO-07Jer.tdb: NBO2, type code %, sha256 30d68ef18e1752dc…

62: PHASE NBO2 % 2 1 2 !
63: CONST NBO2 : NB : O : !

NbO-97Dup-LB.tdb: NBO2, type code %, sha256 7461691cb95cdbdf…

65: PHASE NBO2 % 2 1 2 !
66: CONST NBO2 : NB : O : !

Example references (2 of 2; assessments first):

doi:10.1016/j.jnucmat.2006.10.008 R. Jerlerud Pérez, A.R. Massih, Thermodynamic evaluation of the Nb–O–Zr system, Journal of Nuclear Materials 360, 242-254 (2007).
assessment that models this phase; reports values for this phase
doi:10.1103/physrevb.13.2965 R. Pynn, J. D. Axe, R. Thomas, Structural distortions in the low-temperature phase of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">NbO</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>, Phys. Rev. B 13, 2965-2975 (1976).
cited as the source of values for this phase

O2GAS (Nb–O)

Id: phase:nb-o:o2gas; status assigned
Structure: gas; type st:gas; gas; confidence high
Stability: stable in 2 of 2 calculated diagram(s): 300–1185 K, x(O) 1–1
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (3): corpus: corpus:phase:nb-o:o2gas
tdb: tdb:NbO-07Jer.tdb:O2GAS, tdb:NbO-97Dup-LB.tdb:O2GAS

TDB models of O2GAS (2): PHASE and CONSTITUENT statements as written

NbO-07Jer.tdb: O2GAS, type code %, sha256 30d68ef18e1752dc…

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

NbO-97Dup-LB.tdb: O2GAS, type code %, sha256 7461691cb95cdbdf…

73: PHASE O2GAS % 1 1 !
74: CONST O2GAS : O2 :!

Example references (1 of 1; assessments first):

doi:10.1016/j.jnucmat.2006.10.008 R. Jerlerud Pérez, A.R. Massih, Thermodynamic evaluation of the Nb–O–Zr system, Journal of Nuclear Materials 360, 242-254 (2007).
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}
}