Nb–Ta phases

5 phases (tier A 4, liquid 1); 3 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–Ta system page · Markdown · field reference

Phases of the Nb–Ta system (5)
Phase	Structure	Basis	Stability (calculated)	TDB models
BCC_A2 phase:nb-ta:bcc-a2	W · A2 · cI2 · Im-3m (229)	tier A: standard phase name	stable in 3 of 3 calculated diagram(s): 300–4000 K, x(Ta) 0–1	4
B2_BCC phase:nb-ta:bcc-b2	CsCl · B2 · cP2 · Pm-3m (221)	tier A: standard phase name	stable in 1 of 1 calculated diagram(s): 2780–2910 K	1
FCC_A1 phase:nb-ta:fcc-a1	Cu · A1 · cF4 · Fm-3m (225)	tier A: standard phase name	not stable in 3 calculated diagram(s)	3
HCP_A3 phase:nb-ta:hcp-a3	Mg · A3 · hP2 · P6_3/mmc (194)	tier A: standard phase name	not stable in 3 calculated diagram(s)	3
LIQUID phase:nb-ta:liquid	liquid	liquid	stable in 3 of 3 calculated diagram(s): 2733.4–4000 K, x(Ta) 0–1	3

BCC_A2 (Nb–Ta)

Id: phase:nb-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): 300–4000 K, x(Ta) 0–1
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (5): corpus: corpus:phase:nb-ta:bcc-a2
tdb: tdb:NbTa-02Har.tdb:BCC_A2, tdb:NbTa-04Xio-LB.tdb:BCC_A2, tdb:NbTa-22Zha.tdb:A2_BCC, tdb:NbTa-22Zha.tdb:BCC_A2

TDB models of BCC_A2 (4): PHASE and CONSTITUENT statements as written

NbTa-02Har.tdb: BCC_A2, type code %B, sha256 ca67283e79b7fafa…

30: PHASE BCC_A2 %B 2 1 3 !
31: CONST BCC_A2 : NB% TA% : VA : !

NbTa-04Xio-LB.tdb: BCC_A2, type code %B, sha256 849d2204e0561aeb…

31: PHASE BCC_A2 %B 2 1 3 !
32: CONST BCC_A2 : NB% TA% : VA : !

NbTa-22Zha.tdb: A2_BCC, type code %B, sha256 5229418c54024a1d…

42: PHASE A2_BCC %B 2 1 3 !
43: CONST A2_BCC : NB TA : VA : !

NbTa-22Zha.tdb: BCC_A2, type code %B, sha256 5229418c54024a1d…

37: PHASE BCC_A2 %B 2 1 3 !
38: CONST BCC_A2 : NB% TA% : VA : !

Example references (3 of 3; assessments first):

doi:10.1016/j.calphad.2004.07.002 W. Xiong, Y. Du, Y. Li, B.Y. Huang, H.H. Xu, H.L. Chen, Z. Pan, Calphad, 28, 133-40(2004).
assessment that models this phase
doi:10.1016/j.ijrmhm.2022.105780 Enkuan Zhang, Ying Tang, Mingwen Wen, Abdulmonem Obaied, Irina Roslyakova, Lijun Zhang, On phase stability of Mo-Nb-Ta-W refractory high entropy alloys, International Journal of Refractory Metals and Hard Materials 103, 105780 (2022).
assessment that models this phase
doi:10.1515/ijmr-2002-0196 K.C. Hari Kumar, T. Van Rompaey, P. Wollants, Z. Metallkd., 93, 1146-53(2002).
assessment that models this phase

B2_BCC (Nb–Ta)

Id: phase:nb-ta:bcc-b2; status assigned
Structure: CsCl · B2 · cP2 · Pm-3m (221); type st:b2-cscl-cp2; tier A: standard phase name; confidence high
Caveat: NbTa-22Zha.tdb: ordered phase with disordered part A2_BCC (order/disorder model)
Caveat: partitioned order/disorder model in NbTa-22Zha.tdb also describes the disordered state
Stability: stable in 1 of 1 calculated diagram(s): 2780–2910 K
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (2): corpus: corpus:phase:nb-ta:bcc-b2
tdb: tdb:NbTa-22Zha.tdb:B2_BCC

TDB models of B2_BCC (1): PHASE and CONSTITUENT statements as written

NbTa-22Zha.tdb: B2_BCC, type code %BO, sha256 5229418c54024a1d…

47: PHASE B2_BCC %BO 3 0.5 0.5 3 !
48: CONST B2_BCC : NB TA : NB TA : VA : !

Example references (1 of 1; assessments first):

doi:10.1016/j.ijrmhm.2022.105780 Enkuan Zhang, Ying Tang, Mingwen Wen, Abdulmonem Obaied, Irina Roslyakova, Lijun Zhang, On phase stability of Mo-Nb-Ta-W refractory high entropy alloys, International Journal of Refractory Metals and Hard Materials 103, 105780 (2022).
assessment that models this phase

FCC_A1 (Nb–Ta)

Id: phase:nb-ta:fcc-a1; status assigned
Structure: Cu · A1 · cF4 · Fm-3m (225); type st:a1-cu-cf4; tier A: standard phase name; confidence high
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:nb-ta:fcc-a1
tdb: tdb:NbTa-02Har.tdb:FCC_A1, tdb:NbTa-04Xio-LB.tdb:FCC_A1, tdb:NbTa-22Zha.tdb:FCC_A1

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

NbTa-02Har.tdb: FCC_A1, type code %A, sha256 ca67283e79b7fafa…

25: PHASE FCC_A1 %A 2 1 1 !
26: CONST FCC_A1 : NB TA : VA : !

NbTa-04Xio-LB.tdb: FCC_A1, type code %A, sha256 849d2204e0561aeb…

26: PHASE FCC_A1 %A 2 1 1 !
27: CONST FCC_A1 : NB TA : VA : !

NbTa-22Zha.tdb: FCC_A1, type code %A, sha256 5229418c54024a1d…

32: PHASE FCC_A1 %A 2 1 1 !
33: CONST FCC_A1 : NB TA : VA : !

Example references (3 of 3; assessments first):

doi:10.1016/j.calphad.2004.07.002 W. Xiong, Y. Du, Y. Li, B.Y. Huang, H.H. Xu, H.L. Chen, Z. Pan, Calphad, 28, 133-40(2004).
assessment that models this phase
doi:10.1016/j.ijrmhm.2022.105780 Enkuan Zhang, Ying Tang, Mingwen Wen, Abdulmonem Obaied, Irina Roslyakova, Lijun Zhang, On phase stability of Mo-Nb-Ta-W refractory high entropy alloys, International Journal of Refractory Metals and Hard Materials 103, 105780 (2022).
assessment that models this phase
doi:10.1515/ijmr-2002-0196 K.C. Hari Kumar, T. Van Rompaey, P. Wollants, Z. Metallkd., 93, 1146-53(2002).
assessment that models this phase

HCP_A3 (Nb–Ta)

Id: phase:nb-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
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:nb-ta:hcp-a3
tdb: tdb:NbTa-02Har.tdb:HCP_A3, tdb:NbTa-04Xio-LB.tdb:HCP_A3, tdb:NbTa-22Zha.tdb:HCP_A3

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

NbTa-02Har.tdb: HCP_A3, type code %A, sha256 ca67283e79b7fafa…

35: PHASE HCP_A3 %A 2 1 0.5 !
36: CONST HCP_A3 : NB TA : VA : !

NbTa-04Xio-LB.tdb: HCP_A3, type code %A, sha256 849d2204e0561aeb…

36: PHASE HCP_A3 %A 2 1 0.5 !
37: CONST HCP_A3 : NB TA : VA : !

NbTa-22Zha.tdb: HCP_A3, type code %A, sha256 5229418c54024a1d…

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

Example references (3 of 3; assessments first):

doi:10.1016/j.calphad.2004.07.002 W. Xiong, Y. Du, Y. Li, B.Y. Huang, H.H. Xu, H.L. Chen, Z. Pan, Calphad, 28, 133-40(2004).
assessment that models this phase
doi:10.1016/j.ijrmhm.2022.105780 Enkuan Zhang, Ying Tang, Mingwen Wen, Abdulmonem Obaied, Irina Roslyakova, Lijun Zhang, On phase stability of Mo-Nb-Ta-W refractory high entropy alloys, International Journal of Refractory Metals and Hard Materials 103, 105780 (2022).
assessment that models this phase
doi:10.1515/ijmr-2002-0196 K.C. Hari Kumar, T. Van Rompaey, P. Wollants, Z. Metallkd., 93, 1146-53(2002).
assessment that models this phase

LIQUID (Nb–Ta)

Id: phase:nb-ta:liquid; status assigned
Structure: liquid; type st:liquid; liquid; confidence high
Stability: stable in 3 of 3 calculated diagram(s): 2733.4–4000 K, x(Ta) 0–1
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (4): corpus: corpus:phase:nb-ta:liquid
tdb: tdb:NbTa-02Har.tdb:LIQUID, tdb:NbTa-04Xio-LB.tdb:LIQUID, tdb:NbTa-22Zha.tdb:LIQUID

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

NbTa-02Har.tdb: LIQUID, type code %, sha256 ca67283e79b7fafa…

20: PHASE LIQUID:L % 1 1 !
21: CONST LIQUID:L : NB TA : !

NbTa-04Xio-LB.tdb: LIQUID, type code %, sha256 849d2204e0561aeb…

21: PHASE LIQUID:L % 1 1 !
22: CONST LIQUID:L : NB TA : !

NbTa-22Zha.tdb: LIQUID, type code %, sha256 5229418c54024a1d…

27: PHASE LIQUID:L % 1 1 !
28: CONST LIQUID:L : NB TA : !

Example references (3 of 3; assessments first):

doi:10.1016/j.calphad.2004.07.002 W. Xiong, Y. Du, Y. Li, B.Y. Huang, H.H. Xu, H.L. Chen, Z. Pan, Calphad, 28, 133-40(2004).
assessment that models this phase
doi:10.1016/j.ijrmhm.2022.105780 Enkuan Zhang, Ying Tang, Mingwen Wen, Abdulmonem Obaied, Irina Roslyakova, Lijun Zhang, On phase stability of Mo-Nb-Ta-W refractory high entropy alloys, International Journal of Refractory Metals and Hard Materials 103, 105780 (2022).
assessment that models this phase
doi:10.1515/ijmr-2002-0196 K.C. Hari Kumar, T. Van Rompaey, P. Wollants, Z. Metallkd., 93, 1146-53(2002).
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}
}