N–U phases

11 phases (tier A 5, liquid 1, gas 2, needs_review 3); 9 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 · N–U system page · Markdown · field reference

Phases of the N–U system (11)
Phase	Structure	Basis	Stability (calculated)	Literature values	TDB models
ORTHORHOMBIC_A20 phase:n-u:a20-orthorhombic	alpha-U · A20 · oC4 · Cmcm (63)	tier A: standard phase name	stable in 1 of 1 calculated diagram(s): 300–942.02 K, x(N) 0–0	0	1
BCC_A2 phase:n-u:bcc-a2	W · A2 · cI2 · Im-3m (229)	tier A: standard phase name	stable in 1 of 1 calculated diagram(s): 1048.99–1407.88 K, x(N) 0–0	9	1
FCC_A1 phase:n-u:fcc-a1	Cu · A1 · cF4 · Fm-3m (225)	tier A: standard phase name	not stable in 1 calculated diagram(s)	0	1
FCC_B1 phase:n-u:fcc-b1		needs_review	stable in 1 of 1 calculated diagram(s): 300–3066.3 K, x(N) 0.49679–0.5	113	1
GAS phase:n-u:gas	gas	gas	stable in 1 of 1 calculated diagram(s): 300.02–4000 K, x(N) 0.96215–1	13	1
HCP_A3 phase:n-u:hcp-a3	Mg · A3 · hP2 · P6_3/mmc (194)	tier A: standard phase name	not stable in 1 calculated diagram(s)	0	1
LIQUID phase:n-u:liquid	liquid	liquid	stable in 1 of 1 calculated diagram(s): 1407.88–4000 K, x(N) 0–0.42477	37	1
N2GAS phase:n-u:n2gas	gas	gas	stable in 1 of 1 calculated diagram(s): 300–2171.26 K, x(N) 1–1	0	1
TETRAGONAL_U phase:n-u:u-tetragonal		needs_review	stable in 1 of 1 calculated diagram(s): 942.02–1048.99 K, x(N) 0–0	0	1
U2N3_ALPHA phase:n-u:u2n3-alpha		needs_review	stable in 1 of 1 calculated diagram(s): 300–1175.02 K, x(N) 0.6–0.60684	10	1
U2N3_D52 phase:n-u:u2n3-d52	A-La2O3 · D5_2 · hP5 · P-3m1 (164)	tier A: standard phase name	stable in 1 of 1 calculated diagram(s): 1038.13–1626.26 K, x(N) 0.58678–0.58678	10	1

ORTHORHOMBIC_A20 (N–U)

Id: phase:n-u:a20-orthorhombic; status assigned
Structure: alpha-U · A20 · oC4 · Cmcm (63); type st:a20-alpha-u-oc4; tier A: standard phase name; confidence high
Stoichiometry: U 1.0000
Stability: stable in 1 of 1 calculated diagram(s): 300–942.02 K, x(N) 0–0
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (2): corpus: corpus:phase:n-u:a20-orthorhombic
tdb: tdb:UN-00Che.tdb:ORTHORHOMBIC_A20

TDB models of ORTHORHOMBIC_A20 (1): PHASE and CONSTITUENT statements as written

UN-00Che.tdb: ORTHORHOMBIC_A20, type code %, sha256 690d73c71200efc9…

51: PHASE ORTHORHOMBIC_A20 % 1 1 !
52: CONST ORTHORHOMBIC_A20 : U : !

Example references (1 of 1; assessments first):

doi:10.1016/S0022-3115(00)00043-X P.-Y. Chevalier, E. Fischer, B. Cheynet, J. Nucl. Mater., 280, 136-50(2000).
assessment that models this phase

BCC_A2 (N–U)

Id: phase:n-u: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 1 of 1 calculated diagram(s): 1048.99–1407.88 K, x(N) 0–0
Literature: 9 values (9 accepted) from 1 papers
Interactive: phase registry entry

Names (3): corpus: corpus:phase:n-u:bcc-a2
paper: paper:10.1016/s0022-3115(00)00043-x:γ-U(bcc_A2)
tdb: tdb:UN-00Che.tdb:BCC_A2

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

UN-00Che.tdb: BCC_A2, type code %B, sha256 690d73c71200efc9…

41: PHASE BCC_A2 %B 2 1 3 !
42: CONST BCC_A2 : U : N VA : !

Example references (3 of 3; assessments first):

doi:10.1016/S0022-3115(00)00043-X P.-Y. Chevalier, E. Fischer, B. Cheynet, J. Nucl. Mater., 280, 136-50(2000).
assessment that models this phase; reports values for this phase
doi:10.1016/0364-5916(91)90030-n A.T. Dinsdale, SGTE data for pure elements, Calphad 15, 317-425 (1991).
cited as the source of values for this phase
doi:10.1007/bf02646768 H. Okamoto, N-U (Nitrogen-Uranium), JPE 18, 107-107 (1997).
cited as the source of values for this phase

FCC_A1 (N–U)

Id: phase:n-u: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 1 calculated diagram(s)
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (2): corpus: corpus:phase:n-u:fcc-a1
tdb: tdb:UN-00Che.tdb:FCC_A1

TDB models of FCC_A1 (1): PHASE and CONSTITUENT statements as written

UN-00Che.tdb: FCC_A1, type code %A, sha256 690d73c71200efc9…

36: PHASE FCC_A1 %A 2 1 1 !
37: CONST FCC_A1 : U : N VA : !

Example references (1 of 1; assessments first):

doi:10.1016/S0022-3115(00)00043-X P.-Y. Chevalier, E. Fischer, B. Cheynet, J. Nucl. Mater., 280, 136-50(2000).
assessment that models this phase

FCC_B1 (N–U)

Id: phase:n-u:fcc-b1; status needs_review
No structure assigned. Why: assessment_declared_blocked_by:lattice_word_FCC_contradicts_B1; lattice_word_FCC_contradicts_B1
Candidate (literature_printed): NaCl · cF8 — printed with a label mapped to this phase
Candidate (name_token): NaCl · B1 · cF8 · Fm-3m (225) — Strukturbericht/word 'B1' in the TDB name
Candidate (sgte_mmc2): NaCl · B1 · cF8 · Fm-3m (225) — Hallstedt 2025 mmc2 row for FCC_B1: UN
Candidate (tdb_comment): NaCl · cF8 · Fm-3m — UN-00Che.tdb: 'Prototype NaCl (cF8, Fm-3m)'
Stability: stable in 1 of 1 calculated diagram(s): 300–3066.3 K, x(N) 0.49679–0.5
Literature: 113 values (112 accepted) from 1 papers
Interactive: phase registry entry

Names (5): corpus: corpus:phase:n-u:fcc-b1
paper: paper:10.1016/s0022-3115(00)00043-x:(UN)(fcc_B1), paper:10.1016/s0022-3115(00)00043-x:UN, paper:10.1016/s0022-3115(00)00043-x:UN(fcc_B1)
tdb: tdb:UN-00Che.tdb:FCC_B1

TDB models of FCC_B1 (1): PHASE and CONSTITUENT statements as written

UN-00Che.tdb: FCC_B1, type code %A, sha256 690d73c71200efc9…

61: PHASE FCC_B1 %A 2 1 1 !
62: CONST FCC_B1 : U : N VA : !

Example references (6 of 6; assessments first):

doi:10.1016/S0022-3115(00)00043-X P.-Y. Chevalier, E. Fischer, B. Cheynet, J. Nucl. Mater., 280, 136-50(2000).
assessment that models this phase; reports values for this phase
doi:10.1016/0022-3115(71)90059-6 Y. Takahashi, M. Murabayashi, Y. Akimoto, T. Mukaibo, Uranium mononitride: Heat capacity and thermal conductivity from 298 to 1000 °K, Journal of Nuclear Materials 38, 303-308 (1971).
cited as the source of values for this phase
doi:10.1016/0022-3115(72)90031-1 E.H.P. Cordfunke, R.P. Muis, The heat capacity of uranium mononitride, Journal of Nuclear Materials 42, 233-234 (1972).
cited as the source of values for this phase
doi:10.1007/bf02646768 H. Okamoto, N-U (Nitrogen-Uranium), JPE 18, 107-107 (1997).
cited as the source of values for this phase
doi:10.1063/1.1727621 Edgar F. Westrum, Carolyn M. Barber, Uranium Mononitride: Heat Capacity and Thermodynamic Properties from 5° to 350°K, The Journal of Chemical Physics 45, 635-639 (1966).
cited as the source of values for this phase
doi:10.1039/tf9666201736 J. F. Counsell, R. M. Dell, J. F. Martin, Thermodynamic properties of uranium compounds. Part 2.—Low-temperature heat capacity and entropy of three uranium nitrides, Trans. Faraday Soc. 62, 1736-1747 (1966).
cited as the source of values for this phase

GAS (N–U)

Id: phase:n-u:gas; status assigned
Structure: gas; type st:gas; gas; confidence high
Stability: stable in 1 of 1 calculated diagram(s): 300.02–4000 K, x(N) 0.96215–1
Literature: 13 values (13 accepted) from 1 papers
Interactive: phase registry entry

Names (3): corpus: corpus:phase:n-u:gas
paper: paper:10.1016/s0022-3115(00)00043-x:G
tdb: tdb:UN-00Che.tdb:GAS

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

UN-00Che.tdb: GAS, type code %, sha256 690d73c71200efc9…

77: PHASE GAS:G % 1 1 !
78: CONST GAS:G : N N2 N3 U : !

Example references (2 of 2; assessments first):

doi:10.1016/S0022-3115(00)00043-X P.-Y. Chevalier, E. Fischer, B. Cheynet, J. Nucl. Mater., 280, 136-50(2000).
assessment that models this phase; reports values for this phase
doi:10.1007/bf02646768 H. Okamoto, N-U (Nitrogen-Uranium), JPE 18, 107-107 (1997).
cited as the source of values for this phase

HCP_A3 (N–U)

Id: phase:n-u: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: not stable in 1 calculated diagram(s)
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (2): corpus: corpus:phase:n-u:hcp-a3
tdb: tdb:UN-00Che.tdb:HCP_A3

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

UN-00Che.tdb: HCP_A3, type code %A, sha256 690d73c71200efc9…

46: PHASE HCP_A3 %A 2 1 0.5 !
47: CONST HCP_A3 : U : N VA : !

Example references (1 of 1; assessments first):

doi:10.1016/S0022-3115(00)00043-X P.-Y. Chevalier, E. Fischer, B. Cheynet, J. Nucl. Mater., 280, 136-50(2000).
assessment that models this phase

LIQUID (N–U)

Id: phase:n-u:liquid; status assigned
Structure: liquid; type st:liquid; liquid; confidence high
Stability: stable in 1 of 1 calculated diagram(s): 1407.88–4000 K, x(N) 0–0.42477
Literature: 37 values (37 accepted) from 1 papers
Interactive: phase registry entry

Names (4): corpus: corpus:phase:n-u:liquid
paper: paper:10.1016/s0022-3115(00)00043-x:L, paper:10.1016/s0022-3115(00)00043-x:liquid
tdb: tdb:UN-00Che.tdb:LIQUID

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

UN-00Che.tdb: LIQUID, type code %, sha256 690d73c71200efc9…

31: PHASE LIQUID:L % 1 1 !
32: CONST LIQUID:L : N U UN : !

Example references (3 of 3; assessments first):

doi:10.1016/S0022-3115(00)00043-X P.-Y. Chevalier, E. Fischer, B. Cheynet, J. Nucl. Mater., 280, 136-50(2000).
assessment that models this phase; reports values for this phase
doi:10.1007/bf02646768 H. Okamoto, N-U (Nitrogen-Uranium), JPE 18, 107-107 (1997).
cited as the source of values for this phase
doi:10.1016/0364-5916(91)90030-n A.T. Dinsdale, SGTE data for pure elements, Calphad 15, 317-425 (1991).
cited as the source of values for this phase

N2GAS (N–U)

Id: phase:n-u:n2gas; status assigned
Structure: gas; type st:gas; gas; confidence high
Stability: stable in 1 of 1 calculated diagram(s): 300–2171.26 K, x(N) 1–1
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (2): corpus: corpus:phase:n-u:n2gas
tdb: tdb:UN-00Che.tdb:N2GAS

TDB models of N2GAS (1): PHASE and CONSTITUENT statements as written

UN-00Che.tdb: N2GAS, type code %, sha256 690d73c71200efc9…

74: PHASE N2GAS % 1 1 !
75: CONST N2GAS : N2 : !

Example references (1 of 1; assessments first):

doi:10.1016/S0022-3115(00)00043-X P.-Y. Chevalier, E. Fischer, B. Cheynet, J. Nucl. Mater., 280, 136-50(2000).
assessment that models this phase

TETRAGONAL_U (N–U)

Id: phase:n-u:u-tetragonal; status needs_review
No structure assigned. Why: name_has_descriptive_tokens:TETRAGONAL; no_structure_token
Candidate (sgte_mmc2): beta-U · A_b · tP30 · P4_2/mnm (136) — Hallstedt 2025 mmc2 row for TETRAGONAL_U: beta-U
Candidate (tdb_comment): beta-U · tP30 · P4_2/mnm, SB: A_b — UN-00Che.tdb: 'Prototype beta-U (tP30, P4_2/mnm, SB: A_b)'
Stoichiometry: U 1.0000
Stability: stable in 1 of 1 calculated diagram(s): 942.02–1048.99 K, x(N) 0–0
Literature: 0 values (0 accepted) from 0 papers
Interactive: phase registry entry

Names (2): corpus: corpus:phase:n-u:u-tetragonal
tdb: tdb:UN-00Che.tdb:TETRAGONAL_U

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

UN-00Che.tdb: TETRAGONAL_U, type code %, sha256 690d73c71200efc9…

56: PHASE TETRAGONAL_U % 1 1 !
57: CONST TETRAGONAL_U : U : !

Example references (1 of 1; assessments first):

doi:10.1016/S0022-3115(00)00043-X P.-Y. Chevalier, E. Fischer, B. Cheynet, J. Nucl. Mater., 280, 136-50(2000).
assessment that models this phase

U2N3_ALPHA (N–U)

Id: phase:n-u:u2n3-alpha; status needs_review
No structure assigned. Why: no_structure_token; off_stoichiometric_model
Candidate (sgte_mmc2): U2N3-alpha · cI96 · Ia-3 (206) — Hallstedt 2025 mmc2 row for U2N3_ALPHA: U2N3-alpha
Candidate (tdb_comment): U2N3 · cI96 · Ia-3, 206 — UN-00Che.tdb: 'Prototype U2N3 (cI96, Ia-3, 206)'
Stability: stable in 1 of 1 calculated diagram(s): 300–1175.02 K, x(N) 0.6–0.60684
Literature: 10 values (10 accepted) from 1 papers
Interactive: phase registry entry

Names (4): corpus: corpus:phase:n-u:u2n3-alpha
paper: paper:10.1016/s0022-3115(00)00043-x:α-U(ort_A20), paper:10.1016/s0022-3115(00)00043-x:α-U2N3
tdb: tdb:UN-00Che.tdb:U2N3_ALPHA

TDB models of U2N3_ALPHA (1): PHASE and CONSTITUENT statements as written

UN-00Che.tdb: U2N3_ALPHA, type code %, sha256 690d73c71200efc9…

66: PHASE U2N3_ALPHA % 2 2 3 !
67: CONST U2N3_ALPHA : U% VA : N : !

Example references (3 of 3; assessments first):

doi:10.1016/S0022-3115(00)00043-X P.-Y. Chevalier, E. Fischer, B. Cheynet, J. Nucl. Mater., 280, 136-50(2000).
assessment that models this phase; reports values for this phase
doi:10.1007/bf02646768 H. Okamoto, N-U (Nitrogen-Uranium), JPE 18, 107-107 (1997).
cited as the source of values for this phase
doi:10.1016/0364-5916(91)90030-n A.T. Dinsdale, SGTE data for pure elements, Calphad 15, 317-425 (1991).
cited as the source of values for this phase

U2N3_D52 (N–U)

Id: phase:n-u:u2n3-d52; status assigned
Structure: A-La2O3 · D5_2 · hP5 · P-3m1 (164); type st:d5-2-a-la2o3-hp5; tier A: standard phase name; confidence high
Stoichiometry: N 0.5868, U 0.4132
Stability: stable in 1 of 1 calculated diagram(s): 1038.13–1626.26 K, x(N) 0.58678–0.58678
Literature: 10 values (10 accepted) from 1 papers
Interactive: phase registry entry

Names (3): corpus: corpus:phase:n-u:u2n3-d52
paper: paper:10.1016/s0022-3115(00)00043-x:β-U2N3
tdb: tdb:UN-00Che.tdb:U2N3_D52

TDB models of U2N3_D52 (1): PHASE and CONSTITUENT statements as written

UN-00Che.tdb: U2N3_D52, type code %, sha256 690d73c71200efc9…

71: PHASE U2N3_D52 % 2 1 1.42 !
72: CONST U2N3_D52 : U : N : !

Example references (2 of 2; assessments first):

doi:10.1016/S0022-3115(00)00043-X P.-Y. Chevalier, E. Fischer, B. Cheynet, J. Nucl. Mater., 280, 136-50(2000).
assessment that models this phase; reports values for this phase
doi:10.1007/bf02646768 H. Okamoto, N-U (Nitrogen-Uranium), JPE 18, 107-107 (1997).
cited as the source of values for 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}
}