Ho–O phases

7 phases (tier A 2, tier C 3, 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 · Ho–O system page · Markdown · field reference

Phases of the Ho–O system (7)
Phase	Structure	Basis	Stability (calculated)	TDB models
B_R2O3 phase:ho-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:ho-o:bcc-a2	W · A2 · cI2 · Im-3m (229)	tier A: standard phase name	not stable in 1 calculated diagram(s)	1
C_R2O3_D53 phase:ho-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): 300–555 K, x(O) 0.6–0.6	1
H_R2O3 phase:ho-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): 2485–2500 K, x(O) 0.6–0.6	1
HCP_A3 phase:ho-o:hcp-a3	Mg · A3 · hP2 · P6_3/mmc (194)	tier A: standard phase name	stable in 1 of 1 calculated diagram(s): 1672–1747 K, x(O) 0–0	1
ION phase:ho-o:ion	liquid	liquid	stable in 1 of 1 calculated diagram(s): 1672–2500 K, x(O) 0–0.56218	1
O2GAS phase:ho-o:o2gas	gas	gas	stable in 1 of 1 calculated diagram(s): 300–2500 K, x(O) 1–1	1

B_R2O3 (Ho–O)

Id: phase:ho-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:ho-o:b-r2o3
tdb: tdb:HoO-23Nak.tdb:B_R2O3

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

HoO-23Nak.tdb: B_R2O3, type code %, sha256 b0048ff0f3c67c36…

48: PHASE B_R2O3:I % 2 2 3 !
49: CONST B_R2O3:I : HO+3 : O-2 : !

Example references (1 of 1; assessments first):

doi:10.1016/j.calphad.2023.102636 R. Nakazawa, A. Itoh, S. Yasui, M. Kurata, Y. Kobayashi, Calphad, 83, 102636(2023).
assessment that models this phase

BCC_A2 (Ho–O)

Id: phase:ho-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: Ho 1.0000
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:ho-o:bcc-a2
tdb: tdb:HoO-23Nak.tdb:BCC_A2

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

HoO-23Nak.tdb: BCC_A2, type code %B, sha256 b0048ff0f3c67c36…

38: PHASE BCC_A2 %B 2 1 3 !
39: CONST BCC_A2 : HO : VA : !

Example references (1 of 1; assessments first):

doi:10.1016/j.calphad.2023.102636 R. Nakazawa, A. Itoh, S. Yasui, M. Kurata, Y. Kobayashi, Calphad, 83, 102636(2023).
assessment that models this phase

C_R2O3_D53 (Ho–O)

Id: phase:ho-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): 300–555 K, x(O) 0.6–0.6
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (2): corpus: corpus:phase:ho-o:d53-c-r2o3
tdb: tdb:HoO-23Nak.tdb:C_R2O3_D53

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

HoO-23Nak.tdb: C_R2O3_D53, type code %, sha256 b0048ff0f3c67c36…

53: PHASE C_R2O3_D53:I % 2 2 3 !
54: CONST C_R2O3_D53:I : HO+3 : O-2 : !

Example references (1 of 1; assessments first):

doi:10.1016/j.calphad.2023.102636 R. Nakazawa, A. Itoh, S. Yasui, M. Kurata, Y. Kobayashi, Calphad, 83, 102636(2023).
assessment that models this phase

H_R2O3 (Ho–O)

Id: phase:ho-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): 2485–2500 K, x(O) 0.6–0.6
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (2): corpus: corpus:phase:ho-o:h-r2o3
tdb: tdb:HoO-23Nak.tdb:H_R2O3

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

HoO-23Nak.tdb: H_R2O3, type code %, sha256 b0048ff0f3c67c36…

58: PHASE H_R2O3:I % 2 2 3 !
59: CONST H_R2O3:I : HO+3 : O-2 : !

Example references (1 of 1; assessments first):

doi:10.1016/j.calphad.2023.102636 R. Nakazawa, A. Itoh, S. Yasui, M. Kurata, Y. Kobayashi, Calphad, 83, 102636(2023).
assessment that models this phase

HCP_A3 (Ho–O)

Id: phase:ho-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
Stoichiometry: Ho 1.0000
Stability: stable in 1 of 1 calculated diagram(s): 1672–1747 K, x(O) 0–0
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (2): corpus: corpus:phase:ho-o:hcp-a3
tdb: tdb:HoO-23Nak.tdb:HCP_A3

TDB models of HCP_A3 (1): PHASE and CONSTITUENT statements as written

HoO-23Nak.tdb: HCP_A3, type code %A, sha256 b0048ff0f3c67c36…

43: PHASE HCP_A3 %A 2 1 0.5 !
44: CONST HCP_A3 : HO : VA : !

Example references (1 of 1; assessments first):

doi:10.1016/j.calphad.2023.102636 R. Nakazawa, A. Itoh, S. Yasui, M. Kurata, Y. Kobayashi, Calphad, 83, 102636(2023).
assessment that models this phase

ION (Ho–O)

Id: phase:ho-o:ion; status assigned
Structure: liquid; type st:liquid; liquid; confidence high
Stability: stable in 1 of 1 calculated diagram(s): 1672–2500 K, x(O) 0–0.56218
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (2): corpus: corpus:phase:ho-o:ion
tdb: tdb:HoO-23Nak.tdb:ION

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

HoO-23Nak.tdb: ION, type code %, sha256 b0048ff0f3c67c36…

33: PHASE ION:Y % 2 1 1 !
34: CONST ION:Y : HO+3 : O-2 VA : !

Example references (1 of 1; assessments first):

doi:10.1016/j.calphad.2023.102636 R. Nakazawa, A. Itoh, S. Yasui, M. Kurata, Y. Kobayashi, Calphad, 83, 102636(2023).
assessment that models this phase

O2GAS (Ho–O)

Id: phase:ho-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:ho-o:o2gas
tdb: tdb:HoO-23Nak.tdb:O2GAS

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

HoO-23Nak.tdb: O2GAS, type code %, sha256 b0048ff0f3c67c36…

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

Example references (1 of 1; assessments first):

doi:10.1016/j.calphad.2023.102636 R. Nakazawa, A. Itoh, S. Yasui, M. Kurata, Y. Kobayashi, Calphad, 83, 102636(2023).
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}
}