Hf–O phases

9 phases (tier A 4, tier C 2, liquid 1, gas 2); 8 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 · Hf–O system page · Markdown · field reference

Phases of the Hf–O system (9)
Phase	Structure	Basis	Stability (calculated)	TDB models
BCC_A2 phase:hf-o:bcc-a2	W · A2 · cI2 · Im-3m (229)	tier A: standard phase name	stable in 2 of 2 calculated diagram(s): 2015.2–2582.59 K, x(O) 0–0.04924	2
FCC_A1 phase:hf-o:fcc-a1	Cu · A1 · cF4 · Fm-3m (225)	tier A: standard phase name	not stable in 2 calculated diagram(s)	2
GAS phase:hf-o:gas	gas	gas	stable in 2 of 2 calculated diagram(s): 300–4000 K, x(O) 0.99886–1	2
HCP_A3 phase:hf-o:hcp-a3	Mg · A3 · hP2 · P6_3/mmc (194)	tier A: standard phase name	stable in 2 of 2 calculated diagram(s): 300–2771.46 K, x(O) 0–0.2134	2
HFO2_C1 phase:hf-o:hfo2-c1	CaF2 · C1 · cF12 · Fm-3m (225)	tier A: standard phase name	stable in 2 of 2 calculated diagram(s): 2793–3222.7 K, x(O) 0.64795–0.66667	2
HFO2_MONO phase:hf-o:hfo2-mono	ZrO2-m · C43 · mP12 · P2_1/c (14)	tier C: assessor-stated (Hallstedt 2025 crystallographic table)	stable in 2 of 2 calculated diagram(s): 300–2100 K, x(O) 0.66667–0.66667	2
HFO2_TETR phase:hf-o:hfo2-tetr	HgI2 · tP6 · P4_2/nmc (137)	tier C: assessor-stated (Hallstedt 2025 crystallographic table)	stable in 1 of 2 calculated diagram(s): 2100–2793 K, x(O) 0.66667–0.66667	2
ION phase:hf-o:ion	liquid	liquid	stable in 2 of 2 calculated diagram(s): 2506–4000 K, x(O) 0–0.66667	2
O2GAS phase:hf-o:o2gas	gas	gas	stable in 2 of 2 calculated diagram(s): 300–1185 K, x(O) 1–1	2

BCC_A2 (Hf–O)

Id: phase:hf-o: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 2 of 2 calculated diagram(s): 2015.2–2582.59 K, x(O) 0–0.04924
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (3): corpus: corpus:phase:hf-o:bcc-a2
tdb: tdb:HfO-06Shi.tdb:BCC_A2, tdb:HfO-06Wan.tdb:BCC_A2

TDB models of BCC_A2 (2): PHASE and CONSTITUENT statements as written

HfO-06Shi.tdb: BCC_A2, type code %B, sha256 c524a8de35394af9…

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

HfO-06Wan.tdb: BCC_A2, type code %B, sha256 54d88108dcb3dde7…

47: PHASE BCC_A2 %B 2 1 1 !
48: CONST BCC_A2 : HF : O VA% : !

Example references (1 of 1; assessments first):

doi:10.1016/j.calphad.2006.08.006 Dongwon Shin, Raymundo Arróyave, Zi-Kui Liu, Thermodynamic modeling of the Hf–Si–O system, Calphad 30, 375-386 (2006).
assessment that models this phase

FCC_A1 (Hf–O)

Id: phase:hf-o: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 2 calculated diagram(s)
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (3): corpus: corpus:phase:hf-o:fcc-a1
tdb: tdb:HfO-06Shi.tdb:FCC_A1, tdb:HfO-06Wan.tdb:FCC_A1

TDB models of FCC_A1 (2): PHASE and CONSTITUENT statements as written

HfO-06Shi.tdb: FCC_A1, type code %A, sha256 c524a8de35394af9…

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

HfO-06Wan.tdb: FCC_A1, type code %A, sha256 54d88108dcb3dde7…

42: PHASE FCC_A1 %A 2 1 1 !
43: CONST FCC_A1 : HF : O VA% : !

Example references (1 of 1; assessments first):

doi:10.1016/j.calphad.2006.08.006 Dongwon Shin, Raymundo Arróyave, Zi-Kui Liu, Thermodynamic modeling of the Hf–Si–O system, Calphad 30, 375-386 (2006).
assessment that models this phase

GAS (Hf–O)

Id: phase:hf-o:gas; status assigned
Structure: gas; type st:gas; gas; confidence high
Stability: stable in 2 of 2 calculated diagram(s): 300–4000 K, x(O) 0.99886–1
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (3): corpus: corpus:phase:hf-o:gas
tdb: tdb:HfO-06Shi.tdb:GAS, tdb:HfO-06Wan.tdb:GAS

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

HfO-06Shi.tdb: GAS, type code %, sha256 c524a8de35394af9…

69: PHASE GAS:G % 1 1 !
70: CONST GAS:G : HF O O2 O3 HFO HFO2 : !

HfO-06Wan.tdb: GAS, type code %, sha256 54d88108dcb3dde7…

73: PHASE GAS:G % 1 1 !
74: CONST GAS:G : HF O O2 O3 HFO HFO2 : !

Example references (1 of 1; assessments first):

doi:10.1016/j.calphad.2006.08.006 Dongwon Shin, Raymundo Arróyave, Zi-Kui Liu, Thermodynamic modeling of the Hf–Si–O system, Calphad 30, 375-386 (2006).
assessment that models this phase

HCP_A3 (Hf–O)

Id: phase:hf-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
Stability: stable in 2 of 2 calculated diagram(s): 300–2771.46 K, x(O) 0–0.2134
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (3): corpus: corpus:phase:hf-o:hcp-a3
tdb: tdb:HfO-06Shi.tdb:HCP_A3, tdb:HfO-06Wan.tdb:HCP_A3

TDB models of HCP_A3 (2): PHASE and CONSTITUENT statements as written

HfO-06Shi.tdb: HCP_A3, type code %, sha256 c524a8de35394af9…

48: PHASE HCP_A3 % 2 1 0.5 !
49: CONST HCP_A3 : HF : O VA% : !

HfO-06Wan.tdb: HCP_A3, type code %, sha256 54d88108dcb3dde7…

52: PHASE HCP_A3 % 2 1 0.5 !
53: CONST HCP_A3 : HF : O VA% : !

Example references (1 of 1; assessments first):

doi:10.1016/j.calphad.2006.08.006 Dongwon Shin, Raymundo Arróyave, Zi-Kui Liu, Thermodynamic modeling of the Hf–Si–O system, Calphad 30, 375-386 (2006).
assessment that models this phase

HFO2_C1 (Hf–O)

Id: phase:hf-o:hfo2-c1; status assigned
Structure: CaF2 · C1 · cF12 · Fm-3m (225); type st:c1-caf2-cf12; tier A: standard phase name; confidence high
Stability: stable in 2 of 2 calculated diagram(s): 2793–3222.7 K, x(O) 0.64795–0.66667
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (3): corpus: corpus:phase:hf-o:hfo2-c1
tdb: tdb:HfO-06Shi.tdb:HFO2_C1, tdb:HfO-06Wan.tdb:HFO2_C1

TDB models of HFO2_C1 (2): PHASE and CONSTITUENT statements as written

HfO-06Shi.tdb: HFO2_C1, type code %, sha256 c524a8de35394af9…

63: PHASE HFO2_C1 % 1 1 !
64: CONST HFO2_C1 : HFO2 : !

HfO-06Wan.tdb: HFO2_C1, type code %, sha256 54d88108dcb3dde7…

67: PHASE HFO2_C1:I % 2 1 2 !
68: CONST HFO2_C1:I : HF+2 HF+4% : O-2 VA : !

Example references (1 of 1; assessments first):

doi:10.1016/j.calphad.2006.08.006 Dongwon Shin, Raymundo Arróyave, Zi-Kui Liu, Thermodynamic modeling of the Hf–Si–O system, Calphad 30, 375-386 (2006).
assessment that models this phase

HFO2_MONO (Hf–O)

Id: phase:hf-o:hfo2-mono; status assigned
Structure: ZrO2-m · C43 · mP12 · P2_1/c (14); type st:c43-zro2-m-mp12; 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:MONO, no_structure_token); structure as stated in the SGTE crystallographic table for this phase name and system
Stability: stable in 2 of 2 calculated diagram(s): 300–2100 K, x(O) 0.66667–0.66667
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (3): corpus: corpus:phase:hf-o:hfo2-mono
tdb: tdb:HfO-06Shi.tdb:HFO2_MONO, tdb:HfO-06Wan.tdb:HFO2_MONO

TDB models of HFO2_MONO (2): PHASE and CONSTITUENT statements as written

HfO-06Shi.tdb: HFO2_MONO, type code %, sha256 c524a8de35394af9…

53: PHASE HFO2_MONO % 1 1 !
54: CONST HFO2_MONO : HFO2 : !

HfO-06Wan.tdb: HFO2_MONO, type code %, sha256 54d88108dcb3dde7…

57: PHASE HFO2_MONO:I % 2 1 2 !
58: CONST HFO2_MONO:I : HF+4 : O-2 : !

Example references (1 of 1; assessments first):

doi:10.1016/j.calphad.2006.08.006 Dongwon Shin, Raymundo Arróyave, Zi-Kui Liu, Thermodynamic modeling of the Hf–Si–O system, Calphad 30, 375-386 (2006).
assessment that models this phase

HFO2_TETR (Hf–O)

Id: phase:hf-o:hfo2-tetr; status assigned
Structure: HgI2 · tP6 · P4_2/nmc (137); type st:hgi2-tp6; 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:TETR, no_structure_token); structure as stated in the SGTE crystallographic table for this phase name and system
Stability: stable in 1 of 2 calculated diagram(s): 2100–2793 K, x(O) 0.66667–0.66667
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (3): corpus: corpus:phase:hf-o:hfo2-tetr
tdb: tdb:HfO-06Shi.tdb:HFO2_TETR, tdb:HfO-06Wan.tdb:HFO2_TETR

TDB models of HFO2_TETR (2): PHASE and CONSTITUENT statements as written

HfO-06Shi.tdb: HFO2_TETR, type code %, sha256 c524a8de35394af9…

58: PHASE HFO2_TETR % 1 1 !
59: CONST HFO2_TETR : HFO2 : !

HfO-06Wan.tdb: HFO2_TETR, type code %, sha256 54d88108dcb3dde7…

62: PHASE HFO2_TETR:I % 2 1 2 !
63: CONST HFO2_TETR:I : HF+4 : O-2 : !

Example references (1 of 1; assessments first):

doi:10.1016/j.calphad.2006.08.006 Dongwon Shin, Raymundo Arróyave, Zi-Kui Liu, Thermodynamic modeling of the Hf–Si–O system, Calphad 30, 375-386 (2006).
assessment that models this phase

ION (Hf–O)

Id: phase:hf-o:ion; status assigned
Structure: liquid; type st:liquid; liquid; confidence high
Stability: stable in 2 of 2 calculated diagram(s): 2506–4000 K, x(O) 0–0.66667
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (3): corpus: corpus:phase:hf-o:ion
tdb: tdb:HfO-06Shi.tdb:ION, tdb:HfO-06Wan.tdb:ION

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

HfO-06Shi.tdb: ION, type code %, sha256 c524a8de35394af9…

33: PHASE ION:Y % 2 1 1 !
34: CONST ION:Y : HF+4 : O-2 VA : !

HfO-06Wan.tdb: ION, type code %, sha256 54d88108dcb3dde7…

37: PHASE ION:Y % 2 1 1 !
38: CONST ION:Y : HF+4 : O-2 VA : !

Example references (1 of 1; assessments first):

doi:10.1016/j.calphad.2006.08.006 Dongwon Shin, Raymundo Arróyave, Zi-Kui Liu, Thermodynamic modeling of the Hf–Si–O system, Calphad 30, 375-386 (2006).
assessment that models this phase

O2GAS (Hf–O)

Id: phase:hf-o:o2gas; status assigned
Structure: gas; type st:gas; gas; confidence high
Stability: stable in 2 of 2 calculated diagram(s): 300–1185 K, x(O) 1–1
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (3): corpus: corpus:phase:hf-o:o2gas
tdb: tdb:HfO-06Shi.tdb:O2GAS, tdb:HfO-06Wan.tdb:O2GAS

TDB models of O2GAS (2): PHASE and CONSTITUENT statements as written

HfO-06Shi.tdb: O2GAS, type code %, sha256 c524a8de35394af9…

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

HfO-06Wan.tdb: O2GAS, type code %, sha256 54d88108dcb3dde7…

70: PHASE O2GAS % 1 1 !
71: CONST O2GAS : O2 :!

Example references (1 of 1; assessments first):

doi:10.1016/j.calphad.2006.08.006 Dongwon Shin, Raymundo Arróyave, Zi-Kui Liu, Thermodynamic modeling of the Hf–Si–O system, Calphad 30, 375-386 (2006).
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}
}