O–Rh phases

8 phases (tier A 5, liquid 1, gas 2); 6 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 · O–Rh system page · Markdown · field reference

Phases of the O–Rh system (8)
Phase	Structure	Basis	Stability (calculated)	Literature values	TDB models
BCC_A2 phase:o-rh:bcc-a2	W · A2 · cI2 · Im-3m (229)	tier A: standard phase name	not stable in 2 calculated diagram(s)	0	2
FCC_A1 phase:o-rh:fcc-a1	Cu · A1 · cF4 · Fm-3m (225)	tier A: standard phase name	stable in 2 of 2 calculated diagram(s): 300–3999.5 K, x(O) 0–0	0	2
GAS phase:o-rh:gas	gas	gas	stable in 2 of 2 calculated diagram(s): 1423.78–4002.08 K, x(O) 0.27959–1	3	2
HCP_A3 phase:o-rh:hcp-a3	Mg · A3 · hP2 · P6_3/mmc (194)	tier A: standard phase name	not stable in 2 calculated diagram(s)	0	2
ION phase:o-rh:ion	liquid	liquid	stable in 2 of 2 calculated diagram(s): 2237–4002.08 K, x(O) 0–1e-05	0	2
O2GAS phase:o-rh:o2gas	gas	gas	stable in 1 of 2 calculated diagram(s): 300–375 K, x(O) 1–1	0	2
RH2O3_D51 phase:o-rh:rh2o3-d51	alpha-Al2O3 · D5_1 · hR10 · R-3c (167)	tier A: standard phase name	stable in 2 of 2 calculated diagram(s): 300–1423.78 K, x(O) 0.6–0.6	13	2
RHO2_C4 phase:o-rh:rho2-c4	TiO2 · C4 · tP6 · P4_2/mnm (136)	tier A: standard phase name	stable in 1 of 2 calculated diagram(s): 300–375 K, x(O) 0.66667–0.66667	0	2

BCC_A2 (O–Rh)

Id: phase:o-rh:bcc-a2; status assigned
Structure: W · A2 · cI2 · Im-3m (229); type st:a2-w-ci2; tier A: standard phase name; confidence high
Stoichiometry: Rh 1.0000
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:o-rh:bcc-a2
tdb: tdb:RhO-18Gos.tdb:BCC_A2, tdb:RhO-22Lau.tdb:BCC_A2

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

RhO-18Gos.tdb: BCC_A2, type code %B, sha256 bd914914bb3156cf…

46: PHASE BCC_A2 %B 2 1 3 !
47: CONST BCC_A2 : RH : VA : !

RhO-22Lau.tdb: BCC_A2, type code %B, sha256 901d58a456a36a21…

47: PHASE BCC_A2 %B 2 1 3 !
48: CONST BCC_A2 : RH : VA : !

Example references (2 of 2; assessments first):

doi:10.1016/j.jct.2022.106831 C. Laurin, A. Quaini, E. Regnier, A. Laplace, T. Croze, S. Gossé, The metallic palladium-rhodium solution in interaction with oxygen: The Pd-Rh-O phase diagram and thermodynamics, The Journal of Chemical Thermodynamics 172, 106831 (2022).
assessment that models this phase
doi:10.1016/j.jnucmat.2017.12.034 S. Gossé, S. Bordier, C. Guéneau, E. Brackx, R. Domenger, J. Rogez, Thermodynamic assessment of the rhodium-ruthenium-oxygen (Rh-Ru-O) system, Journal of Nuclear Materials 500, 252-264 (2018).
assessment that models this phase

FCC_A1 (O–Rh)

Id: phase:o-rh:fcc-a1; status assigned
Structure: Cu · A1 · cF4 · Fm-3m (225); type st:a1-cu-cf4; tier A: standard phase name; confidence high
Stability: stable in 2 of 2 calculated diagram(s): 300–3999.5 K, x(O) 0–0
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (3): corpus: corpus:phase:o-rh:fcc-a1
tdb: tdb:RhO-18Gos.tdb:FCC_A1, tdb:RhO-22Lau.tdb:FCC_A1

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

RhO-18Gos.tdb: FCC_A1, type code %A, sha256 bd914914bb3156cf…

41: PHASE FCC_A1 %A 2 1 1 !
42: CONST FCC_A1 : RH : VA : !

RhO-22Lau.tdb: FCC_A1, type code %A, sha256 901d58a456a36a21…

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

Example references (2 of 2; assessments first):

doi:10.1016/j.jct.2022.106831 C. Laurin, A. Quaini, E. Regnier, A. Laplace, T. Croze, S. Gossé, The metallic palladium-rhodium solution in interaction with oxygen: The Pd-Rh-O phase diagram and thermodynamics, The Journal of Chemical Thermodynamics 172, 106831 (2022).
assessment that models this phase
doi:10.1016/j.jnucmat.2017.12.034 S. Gossé, S. Bordier, C. Guéneau, E. Brackx, R. Domenger, J. Rogez, Thermodynamic assessment of the rhodium-ruthenium-oxygen (Rh-Ru-O) system, Journal of Nuclear Materials 500, 252-264 (2018).
assessment that models this phase

GAS (O–Rh)

Id: phase:o-rh:gas; status assigned
Structure: gas; type st:gas; gas; confidence high
Stability: stable in 2 of 2 calculated diagram(s): 1423.78–4002.08 K, x(O) 0.27959–1
Literature: 3 values (3 accepted) from 1 papers
Interactive: phase registry entry

Names (4): corpus: corpus:phase:o-rh:gas
paper: paper:10.1016/j.jnucmat.2017.12.034:Gas
tdb: tdb:RhO-18Gos.tdb:GAS, tdb:RhO-22Lau.tdb:GAS

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

RhO-18Gos.tdb: GAS, type code %, sha256 bd914914bb3156cf…

67: PHASE GAS:G % 1 1 !
68: CONST GAS:G : O O2 O3 RH RHO RHO2 : !

RhO-22Lau.tdb: GAS, type code %, sha256 901d58a456a36a21…

68: PHASE GAS:G % 1 1 !
69: CONST GAS:G : O O2 O3 RH RHO RHO2 : !

Example references (4 of 4; assessments first):

doi:10.1016/j.jnucmat.2017.12.034 S. Gossé, S. Bordier, C. Guéneau, E. Brackx, R. Domenger, J. Rogez, Thermodynamic assessment of the rhodium-ruthenium-oxygen (Rh-Ru-O) system, Journal of Nuclear Materials 500, 252-264 (2018).
assessment that models this phase; reports values for this phase
doi:10.1016/j.jct.2022.106831 C. Laurin, A. Quaini, E. Regnier, A. Laplace, T. Croze, S. Gossé, The metallic palladium-rhodium solution in interaction with oxygen: The Pd-Rh-O phase diagram and thermodynamics, The Journal of Chemical Thermodynamics 172, 106831 (2022).
assessment that models this phase
doi:10.1016/0022-5088(68)90070-2 Olaf Muller, Rustum Roy, Formation and stability of the platinum and rhodium oxides at high oxygen pressures and the structures of Pt3O4, β-PtO2 and RhO2, Journal of the Less Common Metals 16, 129-146 (1968).
cited as the source of values for this phase
doi:10.1016/0040-6031(76)80009-3 G. Bayer, H.G. Wiedemann, Bildung und thermische stabilität von rhodium-oxiden, Thermochimica Acta 15, 213-226 (1976).
cited as the source of values for this phase

HCP_A3 (O–Rh)

Id: phase:o-rh: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: Rh 1.0000
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:o-rh:hcp-a3
tdb: tdb:RhO-18Gos.tdb:HCP_A3, tdb:RhO-22Lau.tdb:HCP_A3

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

RhO-18Gos.tdb: HCP_A3, type code %A, sha256 bd914914bb3156cf…

51: PHASE HCP_A3 %A 2 1 0.5 !
52: CONST HCP_A3 : RH : VA : !

RhO-22Lau.tdb: HCP_A3, type code %A, sha256 901d58a456a36a21…

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

Example references (2 of 2; assessments first):

doi:10.1016/j.jct.2022.106831 C. Laurin, A. Quaini, E. Regnier, A. Laplace, T. Croze, S. Gossé, The metallic palladium-rhodium solution in interaction with oxygen: The Pd-Rh-O phase diagram and thermodynamics, The Journal of Chemical Thermodynamics 172, 106831 (2022).
assessment that models this phase
doi:10.1016/j.jnucmat.2017.12.034 S. Gossé, S. Bordier, C. Guéneau, E. Brackx, R. Domenger, J. Rogez, Thermodynamic assessment of the rhodium-ruthenium-oxygen (Rh-Ru-O) system, Journal of Nuclear Materials 500, 252-264 (2018).
assessment that models this phase

ION (O–Rh)

Id: phase:o-rh:ion; status assigned
Structure: liquid; type st:liquid; liquid; confidence high
Stability: stable in 2 of 2 calculated diagram(s): 2237–4002.08 K, x(O) 0–1e-05
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (3): corpus: corpus:phase:o-rh:ion
tdb: tdb:RhO-18Gos.tdb:ION, tdb:RhO-22Lau.tdb:ION

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

RhO-18Gos.tdb: ION, type code %, sha256 bd914914bb3156cf…

36: PHASE ION:Y % 2 1 1 !
37: CONST ION:Y : RH+3 : O-2 VA : !

RhO-22Lau.tdb: ION, type code %, sha256 901d58a456a36a21…

37: PHASE ION:Y % 2 1 1 !
38: CONST ION:Y : RH+3 : O-2 VA : !

Example references (2 of 2; assessments first):

doi:10.1016/j.jct.2022.106831 C. Laurin, A. Quaini, E. Regnier, A. Laplace, T. Croze, S. Gossé, The metallic palladium-rhodium solution in interaction with oxygen: The Pd-Rh-O phase diagram and thermodynamics, The Journal of Chemical Thermodynamics 172, 106831 (2022).
assessment that models this phase
doi:10.1016/j.jnucmat.2017.12.034 S. Gossé, S. Bordier, C. Guéneau, E. Brackx, R. Domenger, J. Rogez, Thermodynamic assessment of the rhodium-ruthenium-oxygen (Rh-Ru-O) system, Journal of Nuclear Materials 500, 252-264 (2018).
assessment that models this phase

O2GAS (O–Rh)

Id: phase:o-rh:o2gas; status assigned
Structure: gas; type st:gas; gas; confidence high
Stability: stable in 1 of 2 calculated diagram(s): 300–375 K, x(O) 1–1
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (3): corpus: corpus:phase:o-rh:o2gas
tdb: tdb:RhO-18Gos.tdb:O2GAS, tdb:RhO-22Lau.tdb:O2GAS

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

RhO-18Gos.tdb: O2GAS, type code %, sha256 bd914914bb3156cf…

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

RhO-22Lau.tdb: O2GAS, type code %, sha256 901d58a456a36a21…

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

Example references (2 of 2; assessments first):

doi:10.1016/j.jct.2022.106831 C. Laurin, A. Quaini, E. Regnier, A. Laplace, T. Croze, S. Gossé, The metallic palladium-rhodium solution in interaction with oxygen: The Pd-Rh-O phase diagram and thermodynamics, The Journal of Chemical Thermodynamics 172, 106831 (2022).
assessment that models this phase
doi:10.1016/j.jnucmat.2017.12.034 S. Gossé, S. Bordier, C. Guéneau, E. Brackx, R. Domenger, J. Rogez, Thermodynamic assessment of the rhodium-ruthenium-oxygen (Rh-Ru-O) system, Journal of Nuclear Materials 500, 252-264 (2018).
assessment that models this phase

RH2O3_D51 (O–Rh)

Id: phase:o-rh:rh2o3-d51; status assigned
Structure: alpha-Al2O3 · D5_1 · hR10 · R-3c (167); type st:d5-1-alpha-al2o3-hr10; tier A: standard phase name; confidence high
Stability: stable in 2 of 2 calculated diagram(s): 300–1423.78 K, x(O) 0.6–0.6
Literature: 13 values (7 accepted) from 1 papers
Interactive: phase registry entry

Names (4): corpus: corpus:phase:o-rh:rh2o3-d51
paper: paper:10.1016/j.jnucmat.2017.12.034:Rh2O3
tdb: tdb:RhO-18Gos.tdb:RH2O3_D51, tdb:RhO-22Lau.tdb:RH2O3_D51

TDB models of RH2O3_D51 (2): PHASE and CONSTITUENT statements as written

RhO-18Gos.tdb: RH2O3_D51, type code %, sha256 bd914914bb3156cf…

56: PHASE RH2O3_D51:I % 2 2 3 !
57: CONST RH2O3_D51:I : RH+3 : O-2 : !

RhO-22Lau.tdb: RH2O3_D51, type code %, sha256 901d58a456a36a21…

57: PHASE RH2O3_D51:I % 2 2 3 !
58: CONST RH2O3_D51:I : RH+3 : O-2 : !

Example references (9 of 9; assessments first):

doi:10.1016/j.jnucmat.2017.12.034 S. Gossé, S. Bordier, C. Guéneau, E. Brackx, R. Domenger, J. Rogez, Thermodynamic assessment of the rhodium-ruthenium-oxygen (Rh-Ru-O) system, Journal of Nuclear Materials 500, 252-264 (2018).
assessment that models this phase; reports values for this phase
doi:10.1016/j.jct.2022.106831 C. Laurin, A. Quaini, E. Regnier, A. Laplace, T. Croze, S. Gossé, The metallic palladium-rhodium solution in interaction with oxygen: The Pd-Rh-O phase diagram and thermodynamics, The Journal of Chemical Thermodynamics 172, 106831 (2022).
assessment that models this phase
doi:10.1016/s0016-7037(97)00209-3 Johan Nell, Hugh ST.C. O'Neill, The Gibbs free energy of formation and heat capacity of β-Rh2O3 and MgRh2O4, the MgORhO phase diagram, and constraints on the stability of Mg2Rh 4+O4, Geochimica et Cosmochimica Acta 61, 4159-4171 (1997).
cited as the source of values for this phase
doi:10.1524/zpch.1969.67.4_6.277 H. Kleykamp, Freie Bildungsenthalpie von Rhodiumsesquioxid*, Zeitschrift für Physikalische Chemie 67, 277-283 (1969).
cited as the source of values for this phase
doi:10.1007/bf02665468 K. T. Jacob, M. V. Sriram, Phase relations and gibbs energies in the system Mn-Rh-O, Metall Mater Trans A 25, 1347-1357 (1994).
cited as the source of values for this phase
doi:10.1016/0022-5088(85)90079-7 C Mallika, O.M Sreedharan, M.S Chandrasekharaiah, Determination of the standard Gibbs energy of formation of Rh2O3(s) and IrO2(s) from solid oxide electrolyte electromotive force measurements, Journal of the Less Common Metals 107, 203-212 (1985).
cited as the source of values for this phase
doi:10.1515/htmp.2000.19.1.11 Κ. T. Jacob,, T. Uda,, Τ. H. Okabe,, Y. Waseda,, The Standard Enthalpy and Entropy of Formation of Rh2O3 - A Third-Law Optimization, High Temperature Materials and Processes 19, 11-16 (2000).
cited as the source of values for this phase
doi:10.1016/0040-6031(76)80009-3 G. Bayer, H.G. Wiedemann, Bildung und thermische stabilität von rhodium-oxiden, Thermochimica Acta 15, 213-226 (1976).
cited as the source of values for this phase
doi:10.1524/zpch.1964.41.1_2.078 Norbert G. Schmahl, Erich Minzl, Die thermische Zersetzung des Rhodium(III)-oxids und deren Beeinflussung durch Legierungsbildung mit Platin und Palladium, Zeitschrift für Physikalische Chemie 41, 78-96 (1964).
cited as the source of values for this phase

RHO2_C4 (O–Rh)

Id: phase:o-rh:rho2-c4; status assigned
Structure: TiO2 · C4 · tP6 · P4_2/mnm (136); type st:c4-tio2-tp6; tier A: standard phase name; confidence high
Stability: stable in 1 of 2 calculated diagram(s): 300–375 K, x(O) 0.66667–0.66667
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (3): corpus: corpus:phase:o-rh:rho2-c4
tdb: tdb:RhO-18Gos.tdb:RHO2_C4, tdb:RhO-22Lau.tdb:RHO2_C4

TDB models of RHO2_C4 (2): PHASE and CONSTITUENT statements as written

RhO-18Gos.tdb: RHO2_C4, type code %, sha256 bd914914bb3156cf…

61: PHASE RHO2_C4:I % 2 1 2 !
62: CONST RHO2_C4:I : RH+4 : O-2 : !

RhO-22Lau.tdb: RHO2_C4, type code %, sha256 901d58a456a36a21…

62: PHASE RHO2_C4:I % 2 1 2 !
63: CONST RHO2_C4:I : RH+4 : O-2 : !

Example references (2 of 2; assessments first):

doi:10.1016/j.jct.2022.106831 C. Laurin, A. Quaini, E. Regnier, A. Laplace, T. Croze, S. Gossé, The metallic palladium-rhodium solution in interaction with oxygen: The Pd-Rh-O phase diagram and thermodynamics, The Journal of Chemical Thermodynamics 172, 106831 (2022).
assessment that models this phase
doi:10.1016/j.jnucmat.2017.12.034 S. Gossé, S. Bordier, C. Guéneau, E. Brackx, R. Domenger, J. Rogez, Thermodynamic assessment of the rhodium-ruthenium-oxygen (Rh-Ru-O) system, Journal of Nuclear Materials 500, 252-264 (2018).
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}
}