# Np–U phases > Np–U system: 9 phases (tier A 6, liquid 1, needs_review 2); 7 stable in a calculated diagram in the ORCHID phase registry, with names, structure type when the stored evidence supports an assignment under the stated tier rules, calculated stability, verbatim TDB PHASE/CONSTITUENT statements and example references. HTML: https://data.orchid-project.org/phases/pages/NP-U.html · Markdown: https://data.orchid-project.org/phases/pages/NP-U.md 9 phases (tier A 6, liquid 1, needs_review 2); 7 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](https://orchid-project.org/phases/?q=NP-U) · [full JSON](https://data.orchid-project.org/phases/systems/NP-U.json) · [Np–U system page](https://data.orchid-project.org/systems/NP-U.html) · [Markdown](https://data.orchid-project.org/phases/pages/NP-U.md) · [field reference](https://data.orchid-project.org/phases/SCHEMA.md) Table: Phases of the Np–U system (9) | Phase | Structure | Basis | Stability (calculated) | Literature values | TDB models | |---|---|---|---|---:|---:| | [ORTHORHOMBIC_A20](#phase-np-u-a20-orthorhombic); _phase:np-u:a20-orthorhombic_ | alpha-U · A20 · oC4 · Cmcm (63) | tier A: standard phase name | stable in 2 of 2 calculated diagram(s): 300–942.02 K, x(U) 0.53691–1 | 0 | 2 | | [TETRAG_AD](#phase-np-u-ad-tetrag); _phase:np-u:ad-tetrag_ | beta-Np · A_d · tP4 · P4/nmm (129) | tier A: standard phase name | stable in 2 of 2 calculated diagram(s): 458.9–896.5 K, x(U) 0–0.26653 | 0 | 2 | | [BCC_A2](#phase-np-u-bcc-a2); _phase:np-u:bcc-a2_ | W · A2 · cI2 · Im-3m (229) | tier A: standard phase name | stable in 2 of 2 calculated diagram(s): 856.06–2542.99 K, x(U) 0–1 | 0 | 2 | | [FCC_A1](#phase-np-u-fcc-a1); _phase:np-u:fcc-a1_ | Cu · A1 · cF4 · Fm-3m (225) | tier A: standard phase name | not stable in 2 calculated diagram(s) | 0 | 2 | | [HCP_A3](#phase-np-u-hcp-a3); _phase:np-u:hcp-a3_ | Mg · A3 · hP2 · P6_3/mmc (194) | tier A: standard phase name | not stable in 2 calculated diagram(s) | 0 | 2 | | [LIQUID](#phase-np-u-liquid); _phase:np-u:liquid_ | liquid | liquid | stable in 2 of 2 calculated diagram(s): 917.28–4000 K, x(U) 0–1 | 0 | 2 | | [NPU_ZETA](#phase-np-u-npu-zeta); _phase:np-u:npu-zeta_ | | needs_review | stable in 2 of 2 calculated diagram(s): 300–946.63 K, x(U) 0.23414–0.71951 | 0 | 2 | | [ORTHO_AC](#phase-np-u-ortho-ac); _phase:np-u:ortho-ac_ | alpha-Np · A_c · oP8 · Pnma (62) | tier A: standard phase name | stable in 2 of 2 calculated diagram(s): 300–555.02 K, x(U) 0–0.1032 | 0 | 2 | | [TETRAGONAL_U](#phase-np-u-u-tetragonal); _phase:np-u:u-tetragonal_ | | needs_review | stable in 2 of 2 calculated diagram(s): 914.55–1048.82 K, x(U) 0.69334–1 | 0 | 2 | ## ORTHORHOMBIC_A20 (Np–U) - Id: `phase:np-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 - Stability: stable in 2 of 2 calculated diagram(s): 300–942.02 K, x(U) 0.53691–1 - Literature: 0 values (0 accepted) from 0 papers - Interactive: [phase registry entry](https://orchid-project.org/phases/#phase:np-u:a20-orthorhombic) Names (3): _corpus: _corpus:phase:np-u:a20-orthorhombic _tdb: _tdb:NpU-10Kur.tdb:ORTHORHOMBIC_A20, tdb:NpU-18Xie.tdb:ORTHORHOMBIC_A20 ### TDB models of ORTHORHOMBIC_A20 (2): PHASE and CONSTITUENT statements as written [NpU-10Kur.tdb](https://orchid-project.org/data/databases/sgte-binary/NpU-10Kur.tdb): ORTHORHOMBIC_A20, type code %, sha256 `f85b49b94decbbee…` ~~~~text 52: PHASE ORTHORHOMBIC_A20 % 1 1 ! 53: CONST ORTHORHOMBIC_A20 : NP U% : ! ~~~~ [NpU-18Xie.tdb](https://orchid-project.org/data/databases/sgte-binary/NpU-18Xie.tdb): ORTHORHOMBIC_A20, type code %, sha256 `1d2cc8e207135d92…` ~~~~text 50: PHASE ORTHORHOMBIC_A20 % 1 1 ! 51: CONST ORTHORHOMBIC_A20 : NP U% : ! ~~~~ Example references (1 of 1; assessments first): - [doi:10.1016/j.commatsci.2017.11.042](https://doi.org/10.1016/j.commatsci.2017.11.042) Wei Xie, Dane Morgan, CALPHAD modeling and ab initio calculations of the Np-U-Zr system, Computational Materials Science 143, 505-514 (2018). _assessment that models this phase_ ## TETRAG_AD (Np–U) - Id: `phase:np-u:ad-tetrag`; status `assigned` - Structure: beta-Np · A_d · tP4 · P4/nmm (129); type `st:a-d-beta-np-tp4`; tier A: standard phase name; confidence high - Stability: stable in 2 of 2 calculated diagram(s): 458.9–896.5 K, x(U) 0–0.26653 - Literature: 0 values (0 accepted) from 0 papers - Interactive: [phase registry entry](https://orchid-project.org/phases/#phase:np-u:ad-tetrag) Names (3): _corpus: _corpus:phase:np-u:ad-tetrag _tdb: _tdb:NpU-10Kur.tdb:TETRAG_AD, tdb:NpU-18Xie.tdb:TETRAG_AD ### TDB models of TETRAG_AD (2): PHASE and CONSTITUENT statements as written [NpU-10Kur.tdb](https://orchid-project.org/data/databases/sgte-binary/NpU-10Kur.tdb): TETRAG_AD, type code %, sha256 `f85b49b94decbbee…` ~~~~text 47: PHASE TETRAG_AD % 1 1 ! 48: CONST TETRAG_AD : NP% U : ! ~~~~ [NpU-18Xie.tdb](https://orchid-project.org/data/databases/sgte-binary/NpU-18Xie.tdb): TETRAG_AD, type code %, sha256 `1d2cc8e207135d92…` ~~~~text 45: PHASE TETRAG_AD % 1 1 ! 46: CONST TETRAG_AD : NP% U : ! ~~~~ Example references (1 of 1; assessments first): - [doi:10.1016/j.commatsci.2017.11.042](https://doi.org/10.1016/j.commatsci.2017.11.042) Wei Xie, Dane Morgan, CALPHAD modeling and ab initio calculations of the Np-U-Zr system, Computational Materials Science 143, 505-514 (2018). _assessment that models this phase_ ## BCC_A2 (Np–U) - Id: `phase:np-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 2 of 2 calculated diagram(s): 856.06–2542.99 K, x(U) 0–1 - Literature: 0 values (0 accepted) from 0 papers - Interactive: [phase registry entry](https://orchid-project.org/phases/#phase:np-u:bcc-a2) Names (3): _corpus: _corpus:phase:np-u:bcc-a2 _tdb: _tdb:NpU-10Kur.tdb:BCC_A2, tdb:NpU-18Xie.tdb:BCC_A2 ### TDB models of BCC_A2 (2): PHASE and CONSTITUENT statements as written [NpU-10Kur.tdb](https://orchid-project.org/data/databases/sgte-binary/NpU-10Kur.tdb): BCC_A2, type code %B, sha256 `f85b49b94decbbee…` ~~~~text 32: PHASE BCC_A2 %B 2 1 3 ! 33: CONST BCC_A2 : NP% U% : VA : ! ~~~~ [NpU-18Xie.tdb](https://orchid-project.org/data/databases/sgte-binary/NpU-18Xie.tdb): BCC_A2, type code %B, sha256 `1d2cc8e207135d92…` ~~~~text 30: PHASE BCC_A2 %B 2 1 3 ! 31: CONST BCC_A2 : NP% U% : VA : ! ~~~~ Example references (1 of 1; assessments first): - [doi:10.1016/j.commatsci.2017.11.042](https://doi.org/10.1016/j.commatsci.2017.11.042) Wei Xie, Dane Morgan, CALPHAD modeling and ab initio calculations of the Np-U-Zr system, Computational Materials Science 143, 505-514 (2018). _assessment that models this phase_ ## FCC_A1 (Np–U) - Id: `phase:np-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 2 calculated diagram(s) - Literature: 0 values (0 accepted) from 0 papers - Interactive: [phase registry entry](https://orchid-project.org/phases/#phase:np-u:fcc-a1) Names (3): _corpus: _corpus:phase:np-u:fcc-a1 _tdb: _tdb:NpU-10Kur.tdb:FCC_A1, tdb:NpU-18Xie.tdb:FCC_A1 ### TDB models of FCC_A1 (2): PHASE and CONSTITUENT statements as written [NpU-10Kur.tdb](https://orchid-project.org/data/databases/sgte-binary/NpU-10Kur.tdb): FCC_A1, type code %A, sha256 `f85b49b94decbbee…` ~~~~text 27: PHASE FCC_A1 %A 2 1 1 ! 28: CONST FCC_A1 : NP U : VA : ! ~~~~ [NpU-18Xie.tdb](https://orchid-project.org/data/databases/sgte-binary/NpU-18Xie.tdb): FCC_A1, type code %A, sha256 `1d2cc8e207135d92…` ~~~~text 25: PHASE FCC_A1 %A 2 1 1 ! 26: CONST FCC_A1 : NP U : VA : ! ~~~~ Example references (1 of 1; assessments first): - [doi:10.1016/j.commatsci.2017.11.042](https://doi.org/10.1016/j.commatsci.2017.11.042) Wei Xie, Dane Morgan, CALPHAD modeling and ab initio calculations of the Np-U-Zr system, Computational Materials Science 143, 505-514 (2018). _assessment that models this phase_ ## HCP_A3 (Np–U) - Id: `phase:np-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 2 calculated diagram(s) - Literature: 0 values (0 accepted) from 0 papers - Interactive: [phase registry entry](https://orchid-project.org/phases/#phase:np-u:hcp-a3) Names (3): _corpus: _corpus:phase:np-u:hcp-a3 _tdb: _tdb:NpU-10Kur.tdb:HCP_A3, tdb:NpU-18Xie.tdb:HCP_A3 ### TDB models of HCP_A3 (2): PHASE and CONSTITUENT statements as written [NpU-10Kur.tdb](https://orchid-project.org/data/databases/sgte-binary/NpU-10Kur.tdb): HCP_A3, type code %A, sha256 `f85b49b94decbbee…` ~~~~text 37: PHASE HCP_A3 %A 2 1 0.5 ! 38: CONST HCP_A3 : NP U : VA : ! ~~~~ [NpU-18Xie.tdb](https://orchid-project.org/data/databases/sgte-binary/NpU-18Xie.tdb): HCP_A3, type code %A, sha256 `1d2cc8e207135d92…` ~~~~text 35: PHASE HCP_A3 %A 2 1 0.5 ! 36: CONST HCP_A3 : NP U : VA : ! ~~~~ Example references (1 of 1; assessments first): - [doi:10.1016/j.commatsci.2017.11.042](https://doi.org/10.1016/j.commatsci.2017.11.042) Wei Xie, Dane Morgan, CALPHAD modeling and ab initio calculations of the Np-U-Zr system, Computational Materials Science 143, 505-514 (2018). _assessment that models this phase_ ## LIQUID (Np–U) - Id: `phase:np-u:liquid`; status `assigned` - Structure: liquid; type `st:liquid`; liquid; confidence high - Stability: stable in 2 of 2 calculated diagram(s): 917.28–4000 K, x(U) 0–1 - Literature: 0 values (0 accepted) from 0 papers - Interactive: [phase registry entry](https://orchid-project.org/phases/#phase:np-u:liquid) Names (3): _corpus: _corpus:phase:np-u:liquid _tdb: _tdb:NpU-10Kur.tdb:LIQUID, tdb:NpU-18Xie.tdb:LIQUID ### TDB models of LIQUID (2): PHASE and CONSTITUENT statements as written [NpU-10Kur.tdb](https://orchid-project.org/data/databases/sgte-binary/NpU-10Kur.tdb): LIQUID, type code %, sha256 `f85b49b94decbbee…` ~~~~text 22: PHASE LIQUID:L % 1 1 ! 23: CONST LIQUID:L : NP U : ! ~~~~ [NpU-18Xie.tdb](https://orchid-project.org/data/databases/sgte-binary/NpU-18Xie.tdb): LIQUID, type code %, sha256 `1d2cc8e207135d92…` ~~~~text 20: PHASE LIQUID:L % 1 1 ! 21: CONST LIQUID:L : NP U : ! ~~~~ Example references (1 of 1; assessments first): - [doi:10.1016/j.commatsci.2017.11.042](https://doi.org/10.1016/j.commatsci.2017.11.042) Wei Xie, Dane Morgan, CALPHAD modeling and ab initio calculations of the Np-U-Zr system, Computational Materials Science 143, 505-514 (2018). _assessment that models this phase_ ## NPU_ZETA (Np–U) - Id: `phase:np-u:npu-zeta`; status `needs_review` - No structure assigned. Why: no_structure_token; off_stoichiometric_model - Candidate (sgte_mmc2): PuU-zeta · hR58 · R-3m (166) — Hallstedt 2025 mmc2 row for NPU_ZETA: NpU-zeta - Candidate (tdb_comment): PuU-zeta · hR58 · R-3m — NpU-10Kur.tdb: 'Prototype PuU-zeta (hR58, R-3m)' - Candidate (tdb_comment): PuU-zeta · hR58 · R-3m — NpU-18Xie.tdb: 'Prototype PuU-zeta (hR58, R-3m)' - Stability: stable in 2 of 2 calculated diagram(s): 300–946.63 K, x(U) 0.23414–0.71951 - Literature: 0 values (0 accepted) from 0 papers - Interactive: [phase registry entry](https://orchid-project.org/phases/#phase:np-u:npu-zeta) Names (3): _corpus: _corpus:phase:np-u:npu-zeta _tdb: _tdb:NpU-10Kur.tdb:NPU_ZETA, tdb:NpU-18Xie.tdb:NPU_ZETA ### TDB models of NPU_ZETA (2): PHASE and CONSTITUENT statements as written [NpU-10Kur.tdb](https://orchid-project.org/data/databases/sgte-binary/NpU-10Kur.tdb): NPU_ZETA, type code %, sha256 `f85b49b94decbbee…` ~~~~text 62: PHASE NPU_ZETA % 1 1 ! 63: CONST NPU_ZETA : NP U : ! ~~~~ [NpU-18Xie.tdb](https://orchid-project.org/data/databases/sgte-binary/NpU-18Xie.tdb): NPU_ZETA, type code %, sha256 `1d2cc8e207135d92…` ~~~~text 60: PHASE NPU_ZETA % 2 1 2 ! 61: CONST NPU_ZETA : NP U : NP U : ! ~~~~ Example references (1 of 1; assessments first): - [doi:10.1016/j.commatsci.2017.11.042](https://doi.org/10.1016/j.commatsci.2017.11.042) Wei Xie, Dane Morgan, CALPHAD modeling and ab initio calculations of the Np-U-Zr system, Computational Materials Science 143, 505-514 (2018). _assessment that models this phase_ ## ORTHO_AC (Np–U) - Id: `phase:np-u:ortho-ac`; status `assigned` - Structure: alpha-Np · A_c · oP8 · Pnma (62); type `st:a-c-alpha-np-op8`; tier A: standard phase name; confidence high - Stability: stable in 2 of 2 calculated diagram(s): 300–555.02 K, x(U) 0–0.1032 - Literature: 0 values (0 accepted) from 0 papers - Interactive: [phase registry entry](https://orchid-project.org/phases/#phase:np-u:ortho-ac) Names (3): _corpus: _corpus:phase:np-u:ortho-ac _tdb: _tdb:NpU-10Kur.tdb:ORTHO_AC, tdb:NpU-18Xie.tdb:ORTHO_AC ### TDB models of ORTHO_AC (2): PHASE and CONSTITUENT statements as written [NpU-10Kur.tdb](https://orchid-project.org/data/databases/sgte-binary/NpU-10Kur.tdb): ORTHO_AC, type code %, sha256 `f85b49b94decbbee…` ~~~~text 42: PHASE ORTHO_AC % 1 1 ! 43: CONST ORTHO_AC : NP% U : ! ~~~~ [NpU-18Xie.tdb](https://orchid-project.org/data/databases/sgte-binary/NpU-18Xie.tdb): ORTHO_AC, type code %, sha256 `1d2cc8e207135d92…` ~~~~text 40: PHASE ORTHO_AC % 1 1 ! 41: CONST ORTHO_AC : NP% U : ! ~~~~ Example references (1 of 1; assessments first): - [doi:10.1016/j.commatsci.2017.11.042](https://doi.org/10.1016/j.commatsci.2017.11.042) Wei Xie, Dane Morgan, CALPHAD modeling and ab initio calculations of the Np-U-Zr system, Computational Materials Science 143, 505-514 (2018). _assessment that models this phase_ ## TETRAGONAL_U (Np–U) - Id: `phase:np-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 — NpU-10Kur.tdb: 'Prototype beta-U (tP30, P4_2/mnm, SB: A_b)' - Candidate (tdb_comment): beta-U · tP30 · P4_2/mnm, SB: A_b — NpU-18Xie.tdb: 'Prototype beta-U (tP30, P4_2/mnm, SB: A_b)' - Stability: stable in 2 of 2 calculated diagram(s): 914.55–1048.82 K, x(U) 0.69334–1 - Literature: 0 values (0 accepted) from 0 papers - Interactive: [phase registry entry](https://orchid-project.org/phases/#phase:np-u:u-tetragonal) Names (3): _corpus: _corpus:phase:np-u:u-tetragonal _tdb: _tdb:NpU-10Kur.tdb:TETRAGONAL_U, tdb:NpU-18Xie.tdb:TETRAGONAL_U ### TDB models of TETRAGONAL_U (2): PHASE and CONSTITUENT statements as written [NpU-10Kur.tdb](https://orchid-project.org/data/databases/sgte-binary/NpU-10Kur.tdb): TETRAGONAL_U, type code %, sha256 `f85b49b94decbbee…` ~~~~text 57: PHASE TETRAGONAL_U % 1 1 ! 58: CONST TETRAGONAL_U : NP U% : ! ~~~~ [NpU-18Xie.tdb](https://orchid-project.org/data/databases/sgte-binary/NpU-18Xie.tdb): TETRAGONAL_U, type code %, sha256 `1d2cc8e207135d92…` ~~~~text 55: PHASE TETRAGONAL_U % 1 1 ! 56: CONST TETRAGONAL_U : NP U% : ! ~~~~ Example references (1 of 1; assessments first): - [doi:10.1016/j.commatsci.2017.11.042](https://doi.org/10.1016/j.commatsci.2017.11.042) Wei Xie, Dane Morgan, CALPHAD modeling and ab initio calculations of the Np-U-Zr system, Computational Materials Science 143, 505-514 (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). https://doi.org/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). https://doi.org/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. ```bibtex @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} } ``` --- Derived data CC BY 4.0 ([licence](https://creativecommons.org/licenses/by/4.0/)): cite the ORCHID phase registry and the sources named on the page (TDB assessments, Hallstedt 2025, Materials Project, OQMD). TDB statements are quoted as written; parameter expressions are not reproduced. Field reference: [SCHEMA.md](https://data.orchid-project.org/phases/SCHEMA.md). Machine-readable guide: [llms.txt](https://data.orchid-project.org/llms.txt).