# O–Ta system

> O–Ta system: 41 accepted literature values (crystal structure 30, invariant reaction 8, phase transition 3) and 0 calculated phase diagram(s) from ORCHID, each value with evidence class, source, page and quote.

HTML: https://data.orchid-project.org/systems/O-TA.html · Markdown: https://data.orchid-project.org/systems/O-TA.md

41 accepted literature values from 2 paper(s) (experimental 23, model 6, DFT 12); 0 calculated phase diagram(s). 10 further extracted value(s) not accepted by the reader-agreement checks are only in the JSON/CSV.

Data: [JSON](https://data.orchid-project.org/literature/systems/O-TA.json) · [CSV](https://data.orchid-project.org/systems/O-TA.csv) · [interactive explorer](https://orchid-project.org/data-explorer/#O-TA) · [phases (8)](https://data.orchid-project.org/phases/pages/O-TA.html) · [papers (bibliography)](https://data.orchid-project.org/bibliography/pages/systems/O-TA.html) · [Markdown](https://data.orchid-project.org/systems/O-TA.md)

Table: Accepted values by evidence class

| Evidence class | Values |
|---|---:|
| experimental | 23 |
| model | 6 |
| DFT | 12 |

Table: Accepted values by property group

| Property group | Values |
|---|---:|
| invariant reaction | 8 |
| phase transition | 3 |
| crystal structure | 30 |

Convex hulls: [Materials Project DFT hull](https://data.orchid-project.org/hulls/dft-mp/O/O-TA.json) · [OQMD DFT hull](https://data.orchid-project.org/hulls/dft-oqmd/O/O-TA.json) · [CALPHAD hull TaO-22Mei-ass](https://data.orchid-project.org/hulls/calphad-sgte/O/O-TA--TaO-22Mei-ass.json) · [CALPHAD hull TaO-22Mei-ion](https://data.orchid-project.org/hulls/calphad-sgte/O/O-TA--TaO-22Mei-ion.json)

## Invariant reactions (literature)

Table: Invariant reactions reported in the literature for the O–Ta system (8)

| T (K) | Reaction / phases | Compositions (mole fraction) | Class | Source | Location | Quote |
|---:|---|---|---|---|---|---|
| 2193.15 | monotectic: liquid1 \<-> bcc + liquid2 | liquid1: Ta 0.724; bcc: Ta 0.949; liquid2: Ta 0.419 | model | [1] Gebauer 2022; _cites Meisner 2022_ [doi](https://doi.org/10.1016/j.calphad.2022.102391) | Table 2, p. 6, row 4; `ORC-TVMKZUZTSK` |  |
| 2153.15 | monotectic: liquid1 \<-> bcc + liquid2 | liquid1: Ta 0.658; bcc: Ta 0.951; liquid2: Ta 0.351 | model | [1] Gebauer 2022 | Table 2, p. 6, row 1; `ORC-DY363KTPXK` |  |
| 2153.15 | monotectic: liquid1 \<-> bcc + liquid2 | liquid1: Ta 0.57; bcc: Ta 0.943; liquid2: Ta 0.35 | experimental | [1] Gebauer 2022; _cites Garg 1996_ [doi](https://doi.org/10.1007/bf02648373) | Table 2, p. 6, row 2; `ORC-MFUOJW5GAA` |  |
| 2011.15 | monotectic: liquid1 \<-> bcc + liquid2 | liquid1: Ta 0.707; bcc: Ta 0.949; liquid2: Ta 0.414 | model | [1] Gebauer 2022; _cites Meisner 2022_ [doi](https://doi.org/10.1016/j.calphad.2022.102391) | Table 2, p. 6, row 3; `ORC-ER6ZWLVSZT` |  |
| 1914.15 | eutectic: liquid2 \<-> bcc + αTa2O5 | liquid2: Ta 0.397; bcc: Ta 0.945; αTa2O5: Ta 0.286 | model | [1] Gebauer 2022; _cites Meisner 2022_ [doi](https://doi.org/10.1016/j.calphad.2022.102391) | Table 2, p. 6, row 8; `ORC-DFPOHVVZZZ` |  |
| 1823.15 | eutectic: liquid2 \<-> bcc + αTa2O5 | liquid2: Ta 0.29; bcc: Ta 0.95; αTa2O5: Ta 0.286 | experimental | [1] Gebauer 2022; _cites Garg 1996_ [doi](https://doi.org/10.1007/bf02648373) | Table 2, p. 6, row 6; `ORC-IG3MISYCJA` |  |
| 1823.15 | eutectic: liquid2 \<-> bcc + αTa2O5 | liquid2: Ta 0.32; bcc: Ta 0.95; αTa2O5: Ta 0.286 | model | [1] Gebauer 2022 | Table 2, p. 6, row 5; `ORC-QDAEEYNA4N` |  |
| 1787.15 | eutectic: liquid2 \<-> bcc + αTa2O5 | liquid2: Ta 0.387; bcc: Ta 0.952; αTa2O5: Ta 0.286 | model | [1] Gebauer 2022; _cites Meisner 2022_ [doi](https://doi.org/10.1016/j.calphad.2022.102391) | Table 2, p. 6, row 7; `ORC-CIKTGAFCMK` |  |

## Other properties

### Phase transition (3)

Table: Phase transition, O–Ta system

| Property | Value | T (K) | Phases / composition | Class | Source | Location | Quote |
|---|---:|---:|---|---|---|---|---|
| Phase transition | 2058 K | 2058 | liquid | experimental | [2] Meisner 2022; _cites ref. 18_ | p. 4; `ORC-3SCLMUUG7U.6796f6` | “The melting temperatures of the α and β phases are 2145 K and 2058 K, respectively \[18\].” |
| Phase transition | 2145 K | 2145 | α-Ta2O5 + liquid | experimental | [2] Meisner 2022; _cites ref. 18_ | p. 4; `ORC-3SCLMUUG7U.2c913f` | “The melting temperatures of the α and β phases are 2145 K and 2058 K, respectively \[18\].” |
| Phase transition | 3290 K | 3290 | liquid | experimental | [2] Meisner 2022; _cites ref. 45_ | p. 8; `ORC-V3KOVNSTYS` | “The liquid is the least understood aspect of the Ta-O system as quantitative measurements are difficult to obtain at ultra-high temperatures (Tm,Ta2O5 = 2145 K \[18\] and Tm,Ta = 3290 K \[45\], where Tm is the melting temperature).” |

### Crystal structure (30)

Table: Crystal structure, O–Ta system

| Property | Value | T (K) | Phases / composition | Class | Source | Location | Quote |
|---|---:|---:|---|---|---|---|---|
| Lattice a | 6.2 not_printed |  | β-Ta2O5 | experimental | [2] Meisner 2022; _cites ref. 16_ | Table 1, p. 27, row 4; `ORC-65MIISY2JS.bc761e` |  |
| Lattice a | 6.22 not_printed |  | β-Ta2O5 | experimental | [2] Meisner 2022; _cites ref. 21_ | Table 1, p. 27, row 2; `ORC-D2XJ55EB5Z.173d67` |  |
| Lattice a | 3.81 not_printed |  | β-Ta2O5 | DFT | [2] Meisner 2022; _cites ref. 27_ | Table 1, p. 27, row 10; `ORC-DMJ62PNVMX.2809c3` |  |
| Lattice a | 7.13 not_printed |  | β-Ta2O5 | DFT | [2] Meisner 2022; _cites ref. 25_ | Table 1, p. 27, row 8; `ORC-DUDXXP7TBC.599a32` |  |
| Lattice a | 6.25 not_printed |  | β-Ta2O5 | DFT | [2] Meisner 2022; _cites ref. 26_ | Table 1, p. 27, row 9; `ORC-ODLNQZJEXX.38a641` |  |
| Lattice a | 3.87 not_printed |  | β-Ta2O5 | DFT | [2] Meisner 2022; _cites ref. 24_ | Table 1, p. 27, row 7; `ORC-WWLKXUPI44.516336` |  |
| Lattice a | 14.65 not_printed |  | β-Ta2O5 | experimental | [2] Meisner 2022; _cites ref. 22_ | Table 1, p. 27, row 3; `ORC-YSN7REEADQ.7c9038` |  |
| Lattice a | 6.2 not_printed | 298.15 | β-Ta2O5 | experimental | [2] Meisner 2022; _cites ref. 23_ | Table 1, p. 27, row 5; `ORC-73DC5KVU6S.fe07fe` |  |
| Lattice a | 6.19 not_printed | 298.15 | β-Ta2O5 | experimental | [2] Meisner 2022; _cites Cardonne_ | Table 1, p. 27, row 6; `ORC-DQO6XZYKKE.461fab` |  |
| Lattice a | 44 not_printed | 298.15 | β-Ta2O5 | experimental | [2] Meisner 2022; _cites ref. 20_ | Table 1, p. 27, row 1; `ORC-VKDDWKPRIF.bc49c3` |  |
| Lattice b | 3.66 not_printed |  | β-Ta2O5 | experimental | [2] Meisner 2022; _cites ref. 16_ | Table 1, p. 27, row 4; `ORC-65MIISY2JS.5d76db` |  |
| Lattice b | 3.68 not_printed |  | β-Ta2O5 | experimental | [2] Meisner 2022; _cites ref. 21_ | Table 1, p. 27, row 2; `ORC-D2XJ55EB5Z.b0d03a` |  |
| Lattice b | 12.79 not_printed |  | β-Ta2O5 | DFT | [2] Meisner 2022; _cites ref. 27_ | Table 1, p. 27, row 10; `ORC-DMJ62PNVMX.319a05` |  |
| Lattice b | 6.03 not_printed |  | β-Ta2O5 | DFT | [2] Meisner 2022; _cites ref. 25_ | Table 1, p. 27, row 8; `ORC-DUDXXP7TBC.b2bbab` |  |
| Lattice b | 7.4 not_printed |  | β-Ta2O5 | DFT | [2] Meisner 2022; _cites ref. 26_ | Table 1, p. 27, row 9; `ORC-ODLNQZJEXX.5532fc` |  |
| Lattice b | 3.9 not_printed |  | β-Ta2O5 | DFT | [2] Meisner 2022; _cites ref. 24_ | Table 1, p. 27, row 7; `ORC-WWLKXUPI44.a193c8` |  |
| Lattice b | 9.4 not_printed |  | β-Ta2O5 | experimental | [2] Meisner 2022; _cites ref. 22_ | Table 1, p. 27, row 3; `ORC-YSN7REEADQ.863847` |  |
| Lattice b | 40.29 not_printed | 298.15 | β-Ta2O5 | experimental | [2] Meisner 2022; _cites ref. 23_ | Table 1, p. 27, row 5; `ORC-73DC5KVU6S.266727` |  |
| Lattice b | 69.55 not_printed | 298.15 | β-Ta2O5 | experimental | [2] Meisner 2022; _cites Cardonne_ | Table 1, p. 27, row 6; `ORC-DQO6XZYKKE.5e513a` |  |
| Lattice b | 3.89 not_printed | 298.15 | β-Ta2O5 | experimental | [2] Meisner 2022; _cites ref. 20_ | Table 1, p. 27, row 1; `ORC-VKDDWKPRIF.964559` |  |
| Lattice c | 3.89 not_printed |  | β-Ta2O5 | experimental | [2] Meisner 2022; _cites ref. 16_ | Table 1, p. 27, row 4; `ORC-65MIISY2JS.c795b3` |  |
| Lattice c | 7.79 not_printed |  | β-Ta2O5 | experimental | [2] Meisner 2022; _cites ref. 21_ | Table 1, p. 27, row 2; `ORC-D2XJ55EB5Z.d9468e` |  |
| Lattice c | 3.79 not_printed |  | β-Ta2O5 | DFT | [2] Meisner 2022; _cites ref. 27_ | Table 1, p. 27, row 10; `ORC-DMJ62PNVMX.832eb2` |  |
| Lattice c | 3.82 not_printed |  | β-Ta2O5 | DFT | [2] Meisner 2022; _cites ref. 25_ | Table 1, p. 27, row 8; `ORC-DUDXXP7TBC.48f62a` |  |
| Lattice c | 3.83 not_printed |  | β-Ta2O5 | DFT | [2] Meisner 2022; _cites ref. 26_ | Table 1, p. 27, row 9; `ORC-ODLNQZJEXX.f61bcb` |  |
| Lattice c | 13.13 not_printed |  | β-Ta2O5 | DFT | [2] Meisner 2022; _cites ref. 24_ | Table 1, p. 27, row 7; `ORC-WWLKXUPI44.9d8721` |  |
| Lattice c | 31.19 not_printed |  | β-Ta2O5 | experimental | [2] Meisner 2022; _cites ref. 22_ | Table 1, p. 27, row 3; `ORC-YSN7REEADQ.b8c81d` |  |
| Lattice c | 3.89 not_printed | 298.15 | β-Ta2O5 | experimental | [2] Meisner 2022; _cites ref. 23_ | Table 1, p. 27, row 5; `ORC-73DC5KVU6S.805fc0` |  |
| Lattice c | 3.89 not_printed | 298.15 | β-Ta2O5 | experimental | [2] Meisner 2022; _cites Cardonne_ | Table 1, p. 27, row 6; `ORC-DQO6XZYKKE.60e88c` |  |
| Lattice c | 6.21 not_printed | 298.15 | β-Ta2O5 | experimental | [2] Meisner 2022; _cites ref. 20_ | Table 1, p. 27, row 1; `ORC-VKDDWKPRIF.6a0684` |  |

## Sources

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

1. 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). [doi:10.1002/adem.202200162](https://doi.org/10.1002/adem.202200162)
2. Kevin J. Meisner, Rahim Zaman, Bi-Cheng Zhou, Thermodynamic modeling of the Ta-O system, Calphad 76, 102391 (2022). [doi:10.1016/j.calphad.2022.102391](https://doi.org/10.1016/j.calphad.2022.102391)

## 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). https://doi.org/10.5281/zenodo.23735569
- R. Arróyave, J. Saal, D. Shin, ORCHID-Hulls: binary convex hulls (Materials Project, OQMD, assessed CALPHAD) (version 2026.10), Zenodo (2026). https://doi.org/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). https://doi.org/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); 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); 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.

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.

```bibtex
@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_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}
}
```

---

Derived data CC BY 4.0 ([licence](https://creativecommons.org/licenses/by/4.0/)): cite ORCHID ([CITATION.cff](https://data.orchid-project.org/CITATION.cff)) and the original sources. Quotes are short excerpts kept so that each value can be checked; they remain under the publishers' copyright and are not relicensed. Source papers, page images and full text are not redistributed. Field reference: [SCHEMA.md](https://data.orchid-project.org/literature/SCHEMA.md). Machine-readable guide: [llms.txt](https://data.orchid-project.org/llms.txt). Found an error? The report link of a value (Markdown: its id, ORC-..., in the Location column) opens a pre-filled GitHub issue, https://github.com/orchid-calphad/orchid-data/issues/new?template=report-value-error.yml&record_id=\<id>, carrying only the record id, source and value; [how to contribute](https://orchid-project.org/contribute/).