O–Ta phases

8 phases (tier A 3, tier C 2, liquid 2, gas 1); 6 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 · O–Ta system page · Markdown · field reference

Phases of the O–Ta system (8)
Phase	Structure	Basis	Stability (calculated)	Literature values	TDB models
BCC_A2 phase:o-ta:bcc-a2	W · A2 · cI2 · Im-3m (229)	tier A: standard phase name	stable in 3 of 3 calculated diagram(s): 300–3762.45 K, x(O) 0–0.05535	4	3
FCC_A1 phase:o-ta:fcc-a1	Cu · A1 · cF4 · Fm-3m (225)	tier A: standard phase name	not stable in 3 calculated diagram(s)	0	3
HCP_A3 phase:o-ta:hcp-a3	Mg · A3 · hP2 · P6_3/mmc (194)	tier A: standard phase name	not stable in 3 calculated diagram(s)	0	3
ION phase:o-ta:ion	liquid	liquid	stable in 2 of 2 calculated diagram(s): 1787.58–4000 K, x(O) 0–0.71429	0	2
LIQUID phase:o-ta:liquid	liquid	liquid	stable in 1 of 3 calculated diagram(s): 1914.25–4000 K, x(O) 0–0.7154	7	3
O2GAS phase:o-ta:o2gas	gas	gas	stable in 3 of 3 calculated diagram(s): 300–4000 K, x(O) 1–1	0	3
TA2O5_HT phase:o-ta:ta2o5-ht	Ta2O5 · tI44 · I4_1/amd (141)	tier C: assessor-stated (Hallstedt 2025 crystallographic table)	stable in 3 of 3 calculated diagram(s): 1592.88–2169.22 K, x(O) 0.71429–0.71429	0	3
TA2O5_LT phase:o-ta:ta2o5-lt	Ta2O5 · oP14 · Pccm (49)	tier C: assessor-stated (Hallstedt 2025 crystallographic table)	stable in 3 of 3 calculated diagram(s): 300–1593.01 K, x(O) 0.71429–0.71429	0	3

BCC_A2 (O–Ta)

Id: phase:o-ta: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 3 of 3 calculated diagram(s): 300–3762.45 K, x(O) 0–0.05535
Literature: 4 values (4 accepted) from 1 papers
Interactive: phase registry entry

Names (5): corpus: corpus:phase:o-ta:bcc-a2
paper: paper:10.1002/adem.202200162:bcc
tdb: tdb:TaO-22Geb.tdb:BCC_A2, tdb:TaO-22Mei-ass.tdb:BCC_A2, tdb:TaO-22Mei-ion.tdb:BCC_A2

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

TaO-22Geb.tdb: BCC_A2, type code %B, sha256 886665f3a1ed281c…

43: PHASE BCC_A2 %B 2 1 3 !
44: CONST BCC_A2 : TA : O VA : !

TaO-22Mei-ass.tdb: BCC_A2, type code %B, sha256 50b2e3a96e3d3b0a…

42: PHASE BCC_A2 %B 2 1 1 !
43: CONST BCC_A2 : TA : O VA : !

TaO-22Mei-ion.tdb: BCC_A2, type code %B, sha256 88e6b32a58541759…

48: PHASE BCC_A2 %B 2 1 1 !
49: CONST BCC_A2 : TA : O VA : !

Example references (4 of 4; assessments first):

doi:10.1002/adem.202200162 Julian Gebauer, Peter Franke, Hans Jürgen Seifert, Thermodynamic Evaluation of the system Ta–O and Preliminary Assessment of the Systems Al–Nb–O and Al–Ta–O, Adv Eng Mater 24 (2022).
assessment that models this phase; reports values for this phase
doi:10.1016/j.calphad.2022.102391 Kevin J. Meisner, Rahim Zaman, Bi-Cheng Zhou, Thermodynamic modeling of the Ta-O system, Calphad 76, 102391 (2022).
assessment that models this phase; cited as the source of values for this phase
doi:10.1007/bf02648373 S. P. Garg, N. Krishnamurthy, A. Awasthi, M. Venkatraman, J. Phase Equilib. 1996, 17, 63.
cited as the source of values for this phase
doi:10.1016/0022-5088(72)90062-8 H. Jehn, E. Olzi, J. Less-Common Met. 1972, 27, 297.
cited as the source of values for this phase

FCC_A1 (O–Ta)

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

Names (4): corpus: corpus:phase:o-ta:fcc-a1
tdb: tdb:TaO-22Geb.tdb:FCC_A1, tdb:TaO-22Mei-ass.tdb:FCC_A1, tdb:TaO-22Mei-ion.tdb:FCC_A1

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

TaO-22Geb.tdb: FCC_A1, type code %A, sha256 886665f3a1ed281c…

38: PHASE FCC_A1 %A 2 1 1 !
39: CONST FCC_A1 : TA : VA : !

TaO-22Mei-ass.tdb: FCC_A1, type code %A, sha256 50b2e3a96e3d3b0a…

37: PHASE FCC_A1 %A 2 1 1 !
38: CONST FCC_A1 : TA : VA : !

TaO-22Mei-ion.tdb: FCC_A1, type code %A, sha256 88e6b32a58541759…

43: PHASE FCC_A1 %A 2 1 1 !
44: CONST FCC_A1 : TA : VA : !

Example references (2 of 2; assessments first):

doi:10.1002/adem.202200162 Julian Gebauer, Peter Franke, Hans Jürgen Seifert, Thermodynamic Evaluation of the system Ta–O and Preliminary Assessment of the Systems Al–Nb–O and Al–Ta–O, Adv Eng Mater 24 (2022).
assessment that models this phase
doi:10.1016/j.calphad.2022.102391 Kevin J. Meisner, Rahim Zaman, Bi-Cheng Zhou, Thermodynamic modeling of the Ta-O system, Calphad 76, 102391 (2022).
assessment that models this phase

HCP_A3 (O–Ta)

Id: phase:o-ta:hcp-a3; status assigned
Structure: Mg · A3 · hP2 · P6_3/mmc (194); type st:a3-mg-hp2; tier A: standard phase name; confidence high
Stoichiometry: Ta 1.0000
Stability: not stable in 3 calculated diagram(s)
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (4): corpus: corpus:phase:o-ta:hcp-a3
tdb: tdb:TaO-22Geb.tdb:HCP_A3, tdb:TaO-22Mei-ass.tdb:HCP_A3, tdb:TaO-22Mei-ion.tdb:HCP_A3

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

TaO-22Geb.tdb: HCP_A3, type code %A, sha256 886665f3a1ed281c…

48: PHASE HCP_A3 %A 2 1 0.5 !
49: CONST HCP_A3 : TA : VA : !

TaO-22Mei-ass.tdb: HCP_A3, type code %A, sha256 50b2e3a96e3d3b0a…

47: PHASE HCP_A3 %A 2 1 0.5 !
48: CONST HCP_A3 : TA : VA : !

TaO-22Mei-ion.tdb: HCP_A3, type code %A, sha256 88e6b32a58541759…

53: PHASE HCP_A3 %A 2 1 0.5 !
54: CONST HCP_A3 : TA : VA : !

Example references (2 of 2; assessments first):

doi:10.1002/adem.202200162 Julian Gebauer, Peter Franke, Hans Jürgen Seifert, Thermodynamic Evaluation of the system Ta–O and Preliminary Assessment of the Systems Al–Nb–O and Al–Ta–O, Adv Eng Mater 24 (2022).
assessment that models this phase
doi:10.1016/j.calphad.2022.102391 Kevin J. Meisner, Rahim Zaman, Bi-Cheng Zhou, Thermodynamic modeling of the Ta-O system, Calphad 76, 102391 (2022).
assessment that models this phase

ION (O–Ta)

Id: phase:o-ta:ion; status assigned
Structure: liquid; type st:liquid; liquid; confidence high
Stability: stable in 2 of 2 calculated diagram(s): 1787.58–4000 K, x(O) 0–0.71429
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (3): corpus: corpus:phase:o-ta:ion
tdb: tdb:TaO-22Geb.tdb:ION, tdb:TaO-22Mei-ion.tdb:ION

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

TaO-22Geb.tdb: ION, type code %, sha256 886665f3a1ed281c…

33: PHASE ION:Y % 2 1 1 !
34: CONST ION:Y : TA+2 TA+5 : O-2 VA : !

TaO-22Mei-ion.tdb: ION, type code %, sha256 88e6b32a58541759…

38: PHASE ION:Y % 2 1 1 !
39: CONST ION:Y : TA+5 : O-2 VA : !

Example references (2 of 2; assessments first):

doi:10.1002/adem.202200162 Julian Gebauer, Peter Franke, Hans Jürgen Seifert, Thermodynamic Evaluation of the system Ta–O and Preliminary Assessment of the Systems Al–Nb–O and Al–Ta–O, Adv Eng Mater 24 (2022).
assessment that models this phase
doi:10.1016/j.calphad.2022.102391 Kevin J. Meisner, Rahim Zaman, Bi-Cheng Zhou, Thermodynamic modeling of the Ta-O system, Calphad 76, 102391 (2022).
assessment that models this phase

LIQUID (O–Ta)

Id: phase:o-ta:liquid; status assigned
Structure: liquid; type st:liquid; liquid; confidence high
Stability: stable in 1 of 3 calculated diagram(s): 1914.25–4000 K, x(O) 0–0.7154
Literature: 7 values (7 accepted) from 2 papers
Interactive: phase registry entry

Names (6): corpus: corpus:phase:o-ta:liquid
paper: paper:10.1002/adem.202200162:liquid2, paper:10.1016/j.calphad.2022.102391:liquid
tdb: tdb:TaO-22Geb.tdb:LIQUID, tdb:TaO-22Mei-ass.tdb:LIQUID, tdb:TaO-22Mei-ion.tdb:LIQUID

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

TaO-22Geb.tdb: LIQUID, type code %, sha256 886665f3a1ed281c…

30: PHASE LIQUID:L % 1 1 !
31: CONST LIQUID:L : TA : !

TaO-22Mei-ass.tdb: LIQUID, type code %, sha256 50b2e3a96e3d3b0a…

32: PHASE LIQUID:L % 1 1 !
33: CONST LIQUID:L : O TA TA2O5 : !

TaO-22Mei-ion.tdb: LIQUID, type code %, sha256 88e6b32a58541759…

35: PHASE LIQUID:L % 1 1 !
36: CONST LIQUID:L : TA : !

Example references (4 of 4; assessments first):

doi:10.1016/j.calphad.2022.102391 Kevin J. Meisner, Rahim Zaman, Bi-Cheng Zhou, Thermodynamic modeling of the Ta-O system, Calphad 76, 102391 (2022).
assessment that models this phase; cited as the source of values for this phase; reports values for this phase
doi:10.1002/adem.202200162 Julian Gebauer, Peter Franke, Hans Jürgen Seifert, Thermodynamic Evaluation of the system Ta–O and Preliminary Assessment of the Systems Al–Nb–O and Al–Ta–O, Adv Eng Mater 24 (2022).
assessment that models this phase; reports values for this phase
doi:10.1007/bf02648373 S. P. Garg, N. Krishnamurthy, A. Awasthi, M. Venkatraman, J. Phase Equilib. 1996, 17, 63.
cited as the source of values for this phase
doi:10.1016/0022-5088(72)90062-8 H. Jehn, E. Olzi, J. Less-Common Met. 1972, 27, 297.
cited as the source of values for this phase

O2GAS (O–Ta)

Id: phase:o-ta:o2gas; status assigned
Structure: gas; type st:gas; gas; confidence high
Stability: stable in 3 of 3 calculated diagram(s): 300–4000 K, x(O) 1–1
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (4): corpus: corpus:phase:o-ta:o2gas
tdb: tdb:TaO-22Geb.tdb:O2GAS, tdb:TaO-22Mei-ass.tdb:O2GAS, tdb:TaO-22Mei-ion.tdb:O2GAS

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

TaO-22Geb.tdb: O2GAS, type code %, sha256 886665f3a1ed281c…

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

TaO-22Mei-ass.tdb: O2GAS, type code %, sha256 50b2e3a96e3d3b0a…

60: PHASE O2GAS % 1 1 !
61: CONST O2GAS : O2 :!

TaO-22Mei-ion.tdb: O2GAS, type code %, sha256 88e6b32a58541759…

66: PHASE O2GAS % 1 1 !
67: CONST O2GAS : O2 :!

Example references (2 of 2; assessments first):

doi:10.1002/adem.202200162 Julian Gebauer, Peter Franke, Hans Jürgen Seifert, Thermodynamic Evaluation of the system Ta–O and Preliminary Assessment of the Systems Al–Nb–O and Al–Ta–O, Adv Eng Mater 24 (2022).
assessment that models this phase
doi:10.1016/j.calphad.2022.102391 Kevin J. Meisner, Rahim Zaman, Bi-Cheng Zhou, Thermodynamic modeling of the Ta-O system, Calphad 76, 102391 (2022).
assessment that models this phase

TA2O5_HT (O–Ta)

Id: phase:o-ta:ta2o5-ht; status assigned
Structure: Ta2O5 · tI44 · I4_1/amd (141); type st:ta2o5-ti44; 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 (no_structure_token, polymorph_family:other phases of this system have the same composition); structure as stated in the SGTE crystallographic table for this phase name and system
Stoichiometry: O 0.7143, Ta 0.2857
Stability: stable in 3 of 3 calculated diagram(s): 1592.88–2169.22 K, x(O) 0.71429–0.71429
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (4): corpus: corpus:phase:o-ta:ta2o5-ht
tdb: tdb:TaO-22Geb.tdb:TA2O5_HT, tdb:TaO-22Mei-ass.tdb:TA2O5_HT, tdb:TaO-22Mei-ion.tdb:TA2O5_HT

TDB models of TA2O5_HT (3): PHASE and CONSTITUENT statements as written

TaO-22Geb.tdb: TA2O5_HT, type code %, sha256 886665f3a1ed281c…

58: PHASE TA2O5_HT % 2 2 5 !
59: CONST TA2O5_HT : TA : O : !

TaO-22Mei-ass.tdb: TA2O5_HT, type code %, sha256 50b2e3a96e3d3b0a…

57: PHASE TA2O5_HT % 2 2 5 !
58: CONST TA2O5_HT : TA : O : !

TaO-22Mei-ion.tdb: TA2O5_HT, type code %, sha256 88e6b32a58541759…

63: PHASE TA2O5_HT % 2 2 5 !
64: CONST TA2O5_HT : TA : O : !

Example references (2 of 2; assessments first):

doi:10.1002/adem.202200162 Julian Gebauer, Peter Franke, Hans Jürgen Seifert, Thermodynamic Evaluation of the system Ta–O and Preliminary Assessment of the Systems Al–Nb–O and Al–Ta–O, Adv Eng Mater 24 (2022).
assessment that models this phase
doi:10.1016/j.calphad.2022.102391 Kevin J. Meisner, Rahim Zaman, Bi-Cheng Zhou, Thermodynamic modeling of the Ta-O system, Calphad 76, 102391 (2022).
assessment that models this phase

TA2O5_LT (O–Ta)

Id: phase:o-ta:ta2o5-lt; status assigned
Structure: Ta2O5 · oP14 · Pccm (49); type st:ta2o5-op14; 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 (no_structure_token, polymorph_family:other phases of this system have the same composition); structure as stated in the SGTE crystallographic table for this phase name and system
Stoichiometry: O 0.7143, Ta 0.2857
Stability: stable in 3 of 3 calculated diagram(s): 300–1593.01 K, x(O) 0.71429–0.71429
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (4): corpus: corpus:phase:o-ta:ta2o5-lt
tdb: tdb:TaO-22Geb.tdb:TA2O5_LT, tdb:TaO-22Mei-ass.tdb:TA2O5_LT, tdb:TaO-22Mei-ion.tdb:TA2O5_LT

TDB models of TA2O5_LT (3): PHASE and CONSTITUENT statements as written

TaO-22Geb.tdb: TA2O5_LT, type code %, sha256 886665f3a1ed281c…

53: PHASE TA2O5_LT % 2 2 5 !
54: CONST TA2O5_LT : TA : O : !

TaO-22Mei-ass.tdb: TA2O5_LT, type code %, sha256 50b2e3a96e3d3b0a…

52: PHASE TA2O5_LT % 2 2 5 !
53: CONST TA2O5_LT : TA : O : !

TaO-22Mei-ion.tdb: TA2O5_LT, type code %, sha256 88e6b32a58541759…

58: PHASE TA2O5_LT % 2 2 5 !
59: CONST TA2O5_LT : TA : O : !

Example references (2 of 2; assessments first):

doi:10.1002/adem.202200162 Julian Gebauer, Peter Franke, Hans Jürgen Seifert, Thermodynamic Evaluation of the system Ta–O and Preliminary Assessment of the Systems Al–Nb–O and Al–Ta–O, Adv Eng Mater 24 (2022).
assessment that models this phase
doi:10.1016/j.calphad.2022.102391 Kevin J. Meisner, Rahim Zaman, Bi-Cheng Zhou, Thermodynamic modeling of the Ta-O system, Calphad 76, 102391 (2022).
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}
}