Eu–O phases

8 phases (tier A 1, tier C 5, liquid 1, gas 1); 5 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 · Eu–O system page · Markdown · field reference

Phases of the Eu–O system (8)
Phase	Structure	Basis	Stability (calculated)	TDB models
B_R2O3 phase:eu-o:b-r2o3	B-Sm2O3 · mC30 · C2/m (12)	tier C: assessor-stated (Hallstedt 2025 crystallographic table)	not stable in 1 calculated diagram(s)	1
BCC_A2 phase:eu-o:bcc-a2	W · A2 · cI2 · Im-3m (229)	tier A: standard phase name	stable in 1 of 1 calculated diagram(s): 300–1095 K, x(O) 0–0	1
A_R2O3_D52 phase:eu-o:d52-a-r2o3	A-La2O3 · D5_2 · hP5 · P-3m1 (164)	tier C: assessor-stated (Hallstedt 2025 crystallographic table)	not stable in 1 calculated diagram(s)	1
C_R2O3_D53 phase:eu-o:d53-c-r2o3	Mn2O3 · D5_3 · cI80 · Ia-3 (206)	tier C: assessor-stated (Hallstedt 2025 crystallographic table)	stable in 1 of 1 calculated diagram(s): 300–895 K, x(O) 0.6–0.6	1
H_R2O3 phase:eu-o:h-r2o3	H-La2O3 · hP10 · P6_3/mmc (194)	tier C: assessor-stated (Hallstedt 2025 crystallographic table)	stable in 1 of 1 calculated diagram(s): 2420–2500 K, x(O) 0.6–0.6	1
ION phase:eu-o:ion	liquid	liquid	stable in 1 of 1 calculated diagram(s): 1094–2500 K, x(O) 0–0.57018	1
O2GAS phase:eu-o:o2gas	gas	gas	stable in 1 of 1 calculated diagram(s): 300–2500 K, x(O) 1–1	1
X_R2O3 phase:eu-o:r2o3-x	Nd2O3 · cI26 · Im-3m (229)	tier C: assessor-stated (Hallstedt 2025 crystallographic table)	not stable in 1 calculated diagram(s)	1

B_R2O3 (Eu–O)

Id: phase:eu-o:b-r2o3; status assigned
Structure: B-Sm2O3 · mC30 · C2/m (12); type st:b-sm2o3-mc30; 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 (name_has_descriptive_tokens:B,R2O3, no_structure_token); structure as stated in the SGTE crystallographic table for this phase name and system
Stability: not stable in 1 calculated diagram(s)
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (2): corpus: corpus:phase:eu-o:b-r2o3
tdb: tdb:EuO-07Zin.tdb:B_R2O3

TDB models of B_R2O3 (1): PHASE and CONSTITUENT statements as written

EuO-07Zin.tdb: B_R2O3, type code %, sha256 98ca41c17d4bfe5a…

47: PHASE B_R2O3:I % 2 2 3 !
48: CONST B_R2O3:I : EU+3 : O-2 : !

Example references (1 of 1; assessments first):

doi:10.1016/j.pmatsci.2006.09.002 M ZINKEVICH, Thermodynamics of rare earth sesquioxides, Progress in Materials Science 52, 597-647 (2007).
assessment that models this phase

BCC_A2 (Eu–O)

Id: phase:eu-o:bcc-a2; status assigned
Structure: W · A2 · cI2 · Im-3m (229); type st:a2-w-ci2; tier A: standard phase name; confidence high
Stoichiometry: Eu 1.0000
Stability: stable in 1 of 1 calculated diagram(s): 300–1095 K, x(O) 0–0
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (2): corpus: corpus:phase:eu-o:bcc-a2
tdb: tdb:EuO-07Zin.tdb:BCC_A2

TDB models of BCC_A2 (1): PHASE and CONSTITUENT statements as written

EuO-07Zin.tdb: BCC_A2, type code %B, sha256 98ca41c17d4bfe5a…

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

Example references (1 of 1; assessments first):

doi:10.1016/j.pmatsci.2006.09.002 M ZINKEVICH, Thermodynamics of rare earth sesquioxides, Progress in Materials Science 52, 597-647 (2007).
assessment that models this phase

A_R2O3_D52 (Eu–O)

Id: phase:eu-o:d52-a-r2o3; status assigned
Structure: A-La2O3 · D5_2 · hP5 · P-3m1 (164); type st:d5-2-a-la2o3-hp5; 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 (unrecognised_name_tokens:A,R2O3); structure as stated in the SGTE crystallographic table for this phase name and system
Stability: not stable in 1 calculated diagram(s)
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (2): corpus: corpus:phase:eu-o:d52-a-r2o3
tdb: tdb:EuO-07Zin.tdb:A_R2O3_D52

TDB models of A_R2O3_D52 (1): PHASE and CONSTITUENT statements as written

EuO-07Zin.tdb: A_R2O3_D52, type code %, sha256 98ca41c17d4bfe5a…

42: PHASE A_R2O3_D52:I % 2 2 3 !
43: CONST A_R2O3_D52:I : EU+3 : O-2 : !

Example references (1 of 1; assessments first):

doi:10.1016/j.pmatsci.2006.09.002 M ZINKEVICH, Thermodynamics of rare earth sesquioxides, Progress in Materials Science 52, 597-647 (2007).
assessment that models this phase

C_R2O3_D53 (Eu–O)

Id: phase:eu-o:d53-c-r2o3; status assigned
Structure: Mn2O3 · D5_3 · cI80 · Ia-3 (206); type st:d5-3-mn2o3-ci80; 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 (unrecognised_name_tokens:C,R2O3); structure as stated in the SGTE crystallographic table for this phase name and system
Stability: stable in 1 of 1 calculated diagram(s): 300–895 K, x(O) 0.6–0.6
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (2): corpus: corpus:phase:eu-o:d53-c-r2o3
tdb: tdb:EuO-07Zin.tdb:C_R2O3_D53

TDB models of C_R2O3_D53 (1): PHASE and CONSTITUENT statements as written

EuO-07Zin.tdb: C_R2O3_D53, type code %, sha256 98ca41c17d4bfe5a…

52: PHASE C_R2O3_D53:I % 2 2 3 !
53: CONST C_R2O3_D53:I : EU+3 : O-2 : !

Example references (1 of 1; assessments first):

doi:10.1016/j.pmatsci.2006.09.002 M ZINKEVICH, Thermodynamics of rare earth sesquioxides, Progress in Materials Science 52, 597-647 (2007).
assessment that models this phase

H_R2O3 (Eu–O)

Id: phase:eu-o:h-r2o3; status assigned
Structure: H-La2O3 · hP10 · P6_3/mmc (194); type st:h-la2o3-hp10; 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 (name_has_descriptive_tokens:H,R2O3, no_structure_token); structure as stated in the SGTE crystallographic table for this phase name and system
Stability: stable in 1 of 1 calculated diagram(s): 2420–2500 K, x(O) 0.6–0.6
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (2): corpus: corpus:phase:eu-o:h-r2o3
tdb: tdb:EuO-07Zin.tdb:H_R2O3

TDB models of H_R2O3 (1): PHASE and CONSTITUENT statements as written

EuO-07Zin.tdb: H_R2O3, type code %, sha256 98ca41c17d4bfe5a…

57: PHASE H_R2O3:I % 2 2 3 !
58: CONST H_R2O3:I : EU+3 : O-2 : !

Example references (1 of 1; assessments first):

doi:10.1016/j.pmatsci.2006.09.002 M ZINKEVICH, Thermodynamics of rare earth sesquioxides, Progress in Materials Science 52, 597-647 (2007).
assessment that models this phase

ION (Eu–O)

Id: phase:eu-o:ion; status assigned
Structure: liquid; type st:liquid; liquid; confidence high
Stability: stable in 1 of 1 calculated diagram(s): 1094–2500 K, x(O) 0–0.57018
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (2): corpus: corpus:phase:eu-o:ion
tdb: tdb:EuO-07Zin.tdb:ION

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

EuO-07Zin.tdb: ION, type code %, sha256 98ca41c17d4bfe5a…

32: PHASE ION:Y % 2 1 1 !
33: CONST ION:Y : EU+3 : O-2 VA : !

Example references (1 of 1; assessments first):

doi:10.1016/j.pmatsci.2006.09.002 M ZINKEVICH, Thermodynamics of rare earth sesquioxides, Progress in Materials Science 52, 597-647 (2007).
assessment that models this phase

O2GAS (Eu–O)

Id: phase:eu-o:o2gas; status assigned
Structure: gas; type st:gas; gas; confidence high
Stability: stable in 1 of 1 calculated diagram(s): 300–2500 K, x(O) 1–1
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (2): corpus: corpus:phase:eu-o:o2gas
tdb: tdb:EuO-07Zin.tdb:O2GAS

TDB models of O2GAS (1): PHASE and CONSTITUENT statements as written

EuO-07Zin.tdb: O2GAS, type code %, sha256 98ca41c17d4bfe5a…

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

Example references (1 of 1; assessments first):

doi:10.1016/j.pmatsci.2006.09.002 M ZINKEVICH, Thermodynamics of rare earth sesquioxides, Progress in Materials Science 52, 597-647 (2007).
assessment that models this phase

X_R2O3 (Eu–O)

Id: phase:eu-o:r2o3-x; status assigned
Structure: Nd2O3 · cI26 · Im-3m (229); type st:nd2o3-ci26; 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 (name_has_descriptive_tokens:R2O3,X, no_structure_token); structure as stated in the SGTE crystallographic table for this phase name and system
Stability: not stable in 1 calculated diagram(s)
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (2): corpus: corpus:phase:eu-o:r2o3-x
tdb: tdb:EuO-07Zin.tdb:X_R2O3

TDB models of X_R2O3 (1): PHASE and CONSTITUENT statements as written

EuO-07Zin.tdb: X_R2O3, type code %, sha256 98ca41c17d4bfe5a…

62: PHASE X_R2O3:I % 2 2 3 !
63: CONST X_R2O3:I : EU+3 : O-2 : !

Example references (1 of 1; assessments first):

doi:10.1016/j.pmatsci.2006.09.002 M ZINKEVICH, Thermodynamics of rare earth sesquioxides, Progress in Materials Science 52, 597-647 (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}
}