# Si–U phases

> Si–U system: 15 phases (tier A 9, liquid 1, needs_review 5); 13 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/SI-U.html · Markdown: https://data.orchid-project.org/phases/pages/SI-U.md

15 phases (tier A 9, liquid 1, needs_review 5); 13 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=SI-U) · [full JSON](https://data.orchid-project.org/phases/systems/SI-U.json) · [Si–U system page](https://data.orchid-project.org/systems/SI-U.html) · [Markdown](https://data.orchid-project.org/phases/pages/SI-U.md) · [field reference](https://data.orchid-project.org/phases/SCHEMA.md)

Table: Phases of the Si–U system (15)

| Phase | Structure | Basis | Stability (calculated) | Literature values | TDB models |
|---|---|---|---|---:|---:|
| [ORTHORHOMBIC_A20](#phase-si-u-a20-orthorhombic); _phase:si-u:a20-orthorhombic_ | alpha-U · A20 · oC4 · Cmcm (63) | tier A: standard phase name | stable in 3 of 3 calculated diagram(s): 300–1047.02 K, x(U) 0.99678–1 | 0 | 3 |
| [DIAMOND_A4](#phase-si-u-a4-diamond); _phase:si-u:a4-diamond_ | C (diamond) · A4 · cF8 · Fd-3m (227) | tier A: standard phase name | stable in 3 of 3 calculated diagram(s): 300–1692.32 K, x(U) 0–0 | 0 | 3 |
| [BCC_A2](#phase-si-u-bcc-a2); _phase:si-u:bcc-a2_ | W · A2 · cI2 · Im-3m (229) | tier A: standard phase name | stable in 3 of 3 calculated diagram(s): 1048.99–3999.24 K, x(U) 0.97214–1 | 0 | 3 |
| [FCC_A1](#phase-si-u-fcc-a1); _phase:si-u:fcc-a1_ | Cu · A1 · cF4 · Fm-3m (225) | tier A: standard phase name | not stable in 3 calculated diagram(s) | 0 | 3 |
| [HCP_A3](#phase-si-u-hcp-a3); _phase:si-u:hcp-a3_ | Mg · A3 · hP2 · P6_3/mmc (194) | tier A: standard phase name | not stable in 3 calculated diagram(s) | 0 | 3 |
| [LIQUID](#phase-si-u-liquid); _phase:si-u:liquid_ | liquid | liquid | stable in 3 of 3 calculated diagram(s): 1249.45–4000 K, x(U) 0–1 | 5 | 3 |
| [SI2U_CC](#phase-si-u-si2u-cc); _phase:si-u:si2u-cc_ |  | needs_review | stable in 3 of 3 calculated diagram(s): 300–1995.22 K, x(U) 0.33333–0.34722 | 0 | 3 |
| [SI2U3_D5A](#phase-si-u-si2u3-d5a); _phase:si-u:si2u3-d5a_ | Si2U3 · D5_a · tP10 · P4/mbm (127) | tier A: standard phase name | stable in 3 of 3 calculated diagram(s): 300–1952.23 K, x(U) 0.6–0.6 | 0 | 3 |
| [SI3U_L12](#phase-si-u-si3u-l12); _phase:si-u:si3u-l12_ | AuCu3 · L1_2 · cP4 · Pm-3m (221) | tier A: standard phase name | stable in 3 of 3 calculated diagram(s): 300–1795.75 K, x(U) 0.25–0.25 | 0 | 3 |
| [SI5U3_C32](#phase-si-u-si5u3-c32); _phase:si-u:si5u3-c32_ |  | needs_review | stable in 3 of 3 calculated diagram(s): 300–2040.44 K, x(U) 0.375–0.375 | 0 | 3 |
| [SIU_B27](#phase-si-u-siu-b27); _phase:si-u:siu-b27_ |  | needs_review | stable in 3 of 3 calculated diagram(s): 300–1871.05 K, x(U) 0.489–0.5 | 0 | 3 |
| [SIU3](#phase-si-u-siu3); _phase:si-u:siu3_ |  | needs_review | stable in 2 of 2 calculated diagram(s): 300–1205.16 K, x(U) 0.75–0.75 | 0 | 2 |
| [SIU3_D0C](#phase-si-u-siu3-d0c); _phase:si-u:siu3-d0c_ | SiU3-lt · D0_c · tI16 · I4/mcm (140) | tier A: standard phase name | stable in 1 of 1 calculated diagram(s): 300–1260 K, x(U) 0.75–0.75 | 0 | 1 |
| [SIU3_L12](#phase-si-u-siu3-l12); _phase:si-u:siu3-l12_ | AuCu3 · L1_2 · cP4 · Pm-3m (221) | tier A: standard phase name | stable in 1 of 1 calculated diagram(s): 1037.98–1200 K, x(U) 0.75–0.75 | 0 | 1 |
| [TETRAGONAL_U](#phase-si-u-u-tetragonal); _phase:si-u:u-tetragonal_ |  | needs_review | stable in 3 of 3 calculated diagram(s): 920.82–1057.52 K, x(U) 0.98734–1 | 0 | 3 |

## ORTHORHOMBIC_A20 (Si–U)

- Id: `phase:si-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 3 of 3 calculated diagram(s): 300–1047.02 K, x(U) 0.99678–1
- Literature: 0 values (0 accepted) from 0 papers
- Interactive: [phase registry entry](https://orchid-project.org/phases/#phase:si-u:a20-orthorhombic)

Names (4): _corpus: _corpus:phase:si-u:a20-orthorhombic  
_tdb: _tdb:SiU-04Che-LB.tdb:ORTHORHOMBIC_A20, tdb:SiU-09Ber.tdb:ORTHORHOMBIC_A20, tdb:SiU-98AEA.tdb:ORTHORHOMBIC_A20  


### TDB models of ORTHORHOMBIC_A20 (3): PHASE and CONSTITUENT statements as written

[SiU-04Che-LB.tdb](https://orchid-project.org/data/databases/sgte-binary/SiU-04Che-LB.tdb): ORTHORHOMBIC_A20, type code %, sha256 `84486566b19cb138…`

~~~~text
53: PHASE ORTHORHOMBIC_A20 % 1 1 !
54: CONST ORTHORHOMBIC_A20 : SI U% : !
~~~~

[SiU-09Ber.tdb](https://orchid-project.org/data/databases/sgte-binary/SiU-09Ber.tdb): ORTHORHOMBIC_A20, type code %, sha256 `145f0a0d4b59bca1…`

~~~~text
47: PHASE ORTHORHOMBIC_A20 % 1 1 !
48: CONST ORTHORHOMBIC_A20 : U : !
~~~~

[SiU-98AEA.tdb](https://orchid-project.org/data/databases/sgte-binary/SiU-98AEA.tdb): ORTHORHOMBIC_A20, type code %, sha256 `ad20359bfb8262bf…`

~~~~text
54: PHASE ORTHORHOMBIC_A20 % 1 1 !
55: CONST ORTHORHOMBIC_A20 : U : !
~~~~

Example references (1 of 1; assessments first): 

- [doi:10.1016/j.jnucmat.2009.01.014](https://doi.org/10.1016/j.jnucmat.2009.01.014) A. Berche, C. Rado, O. Rapaud, C. Guéneau, J. Rogez, Thermodynamic study of the U–Si system, Journal of Nuclear Materials 389, 101-107 (2009).  
_assessment that models this phase_

## DIAMOND_A4 (Si–U)

- Id: `phase:si-u:a4-diamond`; status `assigned`
- Structure: C (diamond) · A4 · cF8 · Fd-3m (227); type `st:a4-c-diamond-cf8`; tier A: standard phase name; confidence high
- Stoichiometry: Si 1.0000
- Stability: stable in 3 of 3 calculated diagram(s): 300–1692.32 K, x(U) 0–0
- Literature: 0 values (0 accepted) from 0 papers
- Interactive: [phase registry entry](https://orchid-project.org/phases/#phase:si-u:a4-diamond)

Names (4): _corpus: _corpus:phase:si-u:a4-diamond  
_tdb: _tdb:SiU-04Che-LB.tdb:DIAMOND_A4, tdb:SiU-09Ber.tdb:DIAMOND_A4, tdb:SiU-98AEA.tdb:DIAMOND_A4  


### TDB models of DIAMOND_A4 (3): PHASE and CONSTITUENT statements as written

[SiU-04Che-LB.tdb](https://orchid-project.org/data/databases/sgte-binary/SiU-04Che-LB.tdb): DIAMOND_A4, type code %, sha256 `84486566b19cb138…`

~~~~text
48: PHASE DIAMOND_A4 % 1 1 !
49: CONST DIAMOND_A4 : SI : !
~~~~

[SiU-09Ber.tdb](https://orchid-project.org/data/databases/sgte-binary/SiU-09Ber.tdb): DIAMOND_A4, type code %, sha256 `145f0a0d4b59bca1…`

~~~~text
42: PHASE DIAMOND_A4 % 1 1 !
43: CONST DIAMOND_A4 : SI : !
~~~~

[SiU-98AEA.tdb](https://orchid-project.org/data/databases/sgte-binary/SiU-98AEA.tdb): DIAMOND_A4, type code %, sha256 `ad20359bfb8262bf…`

~~~~text
49: PHASE DIAMOND_A4 % 1 1 !
50: CONST DIAMOND_A4 : SI : !
~~~~

Example references (1 of 1; assessments first): 

- [doi:10.1016/j.jnucmat.2009.01.014](https://doi.org/10.1016/j.jnucmat.2009.01.014) A. Berche, C. Rado, O. Rapaud, C. Guéneau, J. Rogez, Thermodynamic study of the U–Si system, Journal of Nuclear Materials 389, 101-107 (2009).  
_assessment that models this phase_

## BCC_A2 (Si–U)

- Id: `phase:si-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 3 of 3 calculated diagram(s): 1048.99–3999.24 K, x(U) 0.97214–1
- Literature: 0 values (0 accepted) from 0 papers
- Interactive: [phase registry entry](https://orchid-project.org/phases/#phase:si-u:bcc-a2)

Names (4): _corpus: _corpus:phase:si-u:bcc-a2  
_tdb: _tdb:SiU-04Che-LB.tdb:BCC_A2, tdb:SiU-09Ber.tdb:BCC_A2, tdb:SiU-98AEA.tdb:BCC_A2  


### TDB models of BCC_A2 (3): PHASE and CONSTITUENT statements as written

[SiU-04Che-LB.tdb](https://orchid-project.org/data/databases/sgte-binary/SiU-04Che-LB.tdb): BCC_A2, type code %B, sha256 `84486566b19cb138…`

~~~~text
38: PHASE BCC_A2 %B 2 1 3 !
39: CONST BCC_A2 : SI U% : VA : !
~~~~

[SiU-09Ber.tdb](https://orchid-project.org/data/databases/sgte-binary/SiU-09Ber.tdb): BCC_A2, type code %B, sha256 `145f0a0d4b59bca1…`

~~~~text
32: PHASE BCC_A2 %B 2 1 3 !
33: CONST BCC_A2 : SI U% : VA : !
~~~~

[SiU-98AEA.tdb](https://orchid-project.org/data/databases/sgte-binary/SiU-98AEA.tdb): BCC_A2, type code %B, sha256 `ad20359bfb8262bf…`

~~~~text
39: PHASE BCC_A2 %B 2 1 3 !
40: CONST BCC_A2 : U : VA : !
~~~~

Example references (1 of 1; assessments first): 

- [doi:10.1016/j.jnucmat.2009.01.014](https://doi.org/10.1016/j.jnucmat.2009.01.014) A. Berche, C. Rado, O. Rapaud, C. Guéneau, J. Rogez, Thermodynamic study of the U–Si system, Journal of Nuclear Materials 389, 101-107 (2009).  
_assessment that models this phase_

## FCC_A1 (Si–U)

- Id: `phase:si-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 3 calculated diagram(s)
- Literature: 0 values (0 accepted) from 0 papers
- Interactive: [phase registry entry](https://orchid-project.org/phases/#phase:si-u:fcc-a1)

Names (4): _corpus: _corpus:phase:si-u:fcc-a1  
_tdb: _tdb:SiU-04Che-LB.tdb:FCC_A1, tdb:SiU-09Ber.tdb:FCC_A1, tdb:SiU-98AEA.tdb:FCC_A1  


### TDB models of FCC_A1 (3): PHASE and CONSTITUENT statements as written

[SiU-04Che-LB.tdb](https://orchid-project.org/data/databases/sgte-binary/SiU-04Che-LB.tdb): FCC_A1, type code %A, sha256 `84486566b19cb138…`

~~~~text
33: PHASE FCC_A1 %A 2 1 1 !
34: CONST FCC_A1 : SI U : VA : !
~~~~

[SiU-09Ber.tdb](https://orchid-project.org/data/databases/sgte-binary/SiU-09Ber.tdb): FCC_A1, type code %A, sha256 `145f0a0d4b59bca1…`

~~~~text
27: PHASE FCC_A1 %A 2 1 1 !
28: CONST FCC_A1 : SI U : VA : !
~~~~

[SiU-98AEA.tdb](https://orchid-project.org/data/databases/sgte-binary/SiU-98AEA.tdb): FCC_A1, type code %A, sha256 `ad20359bfb8262bf…`

~~~~text
34: PHASE FCC_A1 %A 2 1 1 !
35: CONST FCC_A1 : SI U : VA : !
~~~~

Example references (1 of 1; assessments first): 

- [doi:10.1016/j.jnucmat.2009.01.014](https://doi.org/10.1016/j.jnucmat.2009.01.014) A. Berche, C. Rado, O. Rapaud, C. Guéneau, J. Rogez, Thermodynamic study of the U–Si system, Journal of Nuclear Materials 389, 101-107 (2009).  
_assessment that models this phase_

## HCP_A3 (Si–U)

- Id: `phase:si-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 3 calculated diagram(s)
- Literature: 0 values (0 accepted) from 0 papers
- Interactive: [phase registry entry](https://orchid-project.org/phases/#phase:si-u:hcp-a3)

Names (4): _corpus: _corpus:phase:si-u:hcp-a3  
_tdb: _tdb:SiU-04Che-LB.tdb:HCP_A3, tdb:SiU-09Ber.tdb:HCP_A3, tdb:SiU-98AEA.tdb:HCP_A3  


### TDB models of HCP_A3 (3): PHASE and CONSTITUENT statements as written

[SiU-04Che-LB.tdb](https://orchid-project.org/data/databases/sgte-binary/SiU-04Che-LB.tdb): HCP_A3, type code %A, sha256 `84486566b19cb138…`

~~~~text
43: PHASE HCP_A3 %A 2 1 0.5 !
44: CONST HCP_A3 : SI U : VA : !
~~~~

[SiU-09Ber.tdb](https://orchid-project.org/data/databases/sgte-binary/SiU-09Ber.tdb): HCP_A3, type code %A, sha256 `145f0a0d4b59bca1…`

~~~~text
37: PHASE HCP_A3 %A 2 1 0.5 !
38: CONST HCP_A3 : SI U : VA : !
~~~~

[SiU-98AEA.tdb](https://orchid-project.org/data/databases/sgte-binary/SiU-98AEA.tdb): HCP_A3, type code %A, sha256 `ad20359bfb8262bf…`

~~~~text
44: PHASE HCP_A3 %A 2 1 0.5 !
45: CONST HCP_A3 : SI U : VA : !
~~~~

Example references (1 of 1; assessments first): 

- [doi:10.1016/j.jnucmat.2009.01.014](https://doi.org/10.1016/j.jnucmat.2009.01.014) A. Berche, C. Rado, O. Rapaud, C. Guéneau, J. Rogez, Thermodynamic study of the U–Si system, Journal of Nuclear Materials 389, 101-107 (2009).  
_assessment that models this phase_

## LIQUID (Si–U)

- Id: `phase:si-u:liquid`; status `assigned`
- Structure: liquid; type `st:liquid`; liquid; confidence high
- Stability: stable in 3 of 3 calculated diagram(s): 1249.45–4000 K, x(U) 0–1
- Literature: 5 values (5 accepted) from 1 papers
- Interactive: [phase registry entry](https://orchid-project.org/phases/#phase:si-u:liquid)

Names (5): _corpus: _corpus:phase:si-u:liquid  
_paper: _paper:10.1016/j.jnucmat.2009.01.014:liquid  
_tdb: _tdb:SiU-04Che-LB.tdb:LIQUID, tdb:SiU-09Ber.tdb:LIQUID, tdb:SiU-98AEA.tdb:LIQUID  


### TDB models of LIQUID (3): PHASE and CONSTITUENT statements as written

[SiU-04Che-LB.tdb](https://orchid-project.org/data/databases/sgte-binary/SiU-04Che-LB.tdb): LIQUID, type code %, sha256 `84486566b19cb138…`

~~~~text
28: PHASE LIQUID:L % 1 1 !
29: CONST LIQUID:L : SI U : !
~~~~

[SiU-09Ber.tdb](https://orchid-project.org/data/databases/sgte-binary/SiU-09Ber.tdb): LIQUID, type code %, sha256 `145f0a0d4b59bca1…`

~~~~text
22: PHASE LIQUID:L % 1 1 !
23: CONST LIQUID:L : SI U : !
~~~~

[SiU-98AEA.tdb](https://orchid-project.org/data/databases/sgte-binary/SiU-98AEA.tdb): LIQUID, type code %, sha256 `ad20359bfb8262bf…`

~~~~text
29: PHASE LIQUID:L % 1 1 !
30: CONST LIQUID:L : SI U : !
~~~~

Example references (1 of 1; assessments first): 

- [doi:10.1016/j.jnucmat.2009.01.014](https://doi.org/10.1016/j.jnucmat.2009.01.014) A. Berche, C. Rado, O. Rapaud, C. Guéneau, J. Rogez, Thermodynamic study of the U–Si system, Journal of Nuclear Materials 389, 101-107 (2009).  
_assessment that models this phase; reports values for this phase_

## SI2U_CC (Si–U)

- Id: `phase:si-u:si2u-cc`; status `needs_review`
- No structure assigned. Why: assessment_declared_blocked_by:models_disagree_on_composition; models_disagree_on_composition; stoichiometry_contradicts_C_c:SiU-04Che-LB.tdb; stoichiometry_contradicts_C_c:SiU-09Ber.tdb
- Candidate (name_token): Si2Th · C_c · tI12 · I4_1/amd (141) — Strukturbericht/word 'CC' in the TDB name
- Candidate (sgte_mmc2): Si2Th · C_c · tI12 · I4_1/amd (141) — Hallstedt 2025 mmc2 row for SI2U_CC: Si2U
- Candidate (tdb_comment): Si2Th · tI12 · I4_1/amd — SiU-04Che-LB.tdb: 'Prototype Si2Th (tI12, I4_1/amd)'
- Candidate (tdb_comment): Si2Th · tI12 · I4_1/amd — SiU-09Ber.tdb: 'Prototype Si2Th (tI12, I4_1/amd)'
- Candidate (tdb_comment): Si2Th · tI12 · I4_1/amd — SiU-98AEA.tdb: 'Prototype Si2Th (tI12, I4_1/amd)'
- Stability: stable in 3 of 3 calculated diagram(s): 300–1995.22 K, x(U) 0.33333–0.34722
- Literature: 0 values (0 accepted) from 0 papers
- Interactive: [phase registry entry](https://orchid-project.org/phases/#phase:si-u:si2u-cc)

Names (4): _corpus: _corpus:phase:si-u:si2u-cc  
_tdb: _tdb:SiU-04Che-LB.tdb:SI2U_CC, tdb:SiU-09Ber.tdb:SI2U_CC, tdb:SiU-98AEA.tdb:SI2U_CC  


### TDB models of SI2U_CC (3): PHASE and CONSTITUENT statements as written

[SiU-04Che-LB.tdb](https://orchid-project.org/data/databases/sgte-binary/SiU-04Che-LB.tdb): SI2U_CC, type code %, sha256 `84486566b19cb138…`

~~~~text
68: PHASE SI2U_CC % 2 47 25 !
69: CONST SI2U_CC : SI : U : !
~~~~

[SiU-09Ber.tdb](https://orchid-project.org/data/databases/sgte-binary/SiU-09Ber.tdb): SI2U_CC, type code %, sha256 `145f0a0d4b59bca1…`

~~~~text
62: PHASE SI2U_CC % 2 1.88 1 !
63: CONST SI2U_CC : SI : U : !
~~~~

[SiU-98AEA.tdb](https://orchid-project.org/data/databases/sgte-binary/SiU-98AEA.tdb): SI2U_CC, type code %, sha256 `ad20359bfb8262bf…`

~~~~text
69: PHASE SI2U_CC % 2 2 1 !
70: CONST SI2U_CC : SI : U : !
~~~~

Example references (1 of 1; assessments first): 

- [doi:10.1016/j.jnucmat.2009.01.014](https://doi.org/10.1016/j.jnucmat.2009.01.014) A. Berche, C. Rado, O. Rapaud, C. Guéneau, J. Rogez, Thermodynamic study of the U–Si system, Journal of Nuclear Materials 389, 101-107 (2009).  
_assessment that models this phase_

## SI2U3_D5A (Si–U)

- Id: `phase:si-u:si2u3-d5a`; status `assigned`
- Structure: Si2U3 · D5_a · tP10 · P4/mbm (127); type `st:d5-a-si2u3-tp10`; tier A: standard phase name; confidence high
- Stoichiometry: Si 0.4000, U 0.6000
- Stability: stable in 3 of 3 calculated diagram(s): 300–1952.23 K, x(U) 0.6–0.6
- Literature: 0 values (0 accepted) from 0 papers
- Interactive: [phase registry entry](https://orchid-project.org/phases/#phase:si-u:si2u3-d5a)

Names (4): _corpus: _corpus:phase:si-u:si2u3-d5a  
_tdb: _tdb:SiU-04Che-LB.tdb:SI2U3_D5A, tdb:SiU-09Ber.tdb:SI2U3_D5A, tdb:SiU-98AEA.tdb:SI2U3_D5A  


### TDB models of SI2U3_D5A (3): PHASE and CONSTITUENT statements as written

[SiU-04Che-LB.tdb](https://orchid-project.org/data/databases/sgte-binary/SiU-04Che-LB.tdb): SI2U3_D5A, type code %, sha256 `84486566b19cb138…`

~~~~text
83: PHASE SI2U3_D5A % 2 2 3 !
84: CONST SI2U3_D5A : SI : U : !
~~~~

[SiU-09Ber.tdb](https://orchid-project.org/data/databases/sgte-binary/SiU-09Ber.tdb): SI2U3_D5A, type code %, sha256 `145f0a0d4b59bca1…`

~~~~text
77: PHASE SI2U3_D5A % 2 2 3 !
78: CONST SI2U3_D5A : SI : U : !
~~~~

[SiU-98AEA.tdb](https://orchid-project.org/data/databases/sgte-binary/SiU-98AEA.tdb): SI2U3_D5A, type code %, sha256 `ad20359bfb8262bf…`

~~~~text
84: PHASE SI2U3_D5A % 2 2 3 !
85: CONST SI2U3_D5A : SI : U : !
~~~~

Example references (1 of 1; assessments first): 

- [doi:10.1016/j.jnucmat.2009.01.014](https://doi.org/10.1016/j.jnucmat.2009.01.014) A. Berche, C. Rado, O. Rapaud, C. Guéneau, J. Rogez, Thermodynamic study of the U–Si system, Journal of Nuclear Materials 389, 101-107 (2009).  
_assessment that models this phase_

## SI3U_L12 (Si–U)

- Id: `phase:si-u:si3u-l12`; status `assigned`
- Structure: AuCu3 · L1_2 · cP4 · Pm-3m (221); type `st:l1-2-aucu3-cp4`; tier A: standard phase name; confidence high
- Caveat: DFT agrees: on-hull mp-aaaaaeds and oqmd-18109, space group 221
- Stoichiometry: Si 0.7500, U 0.2500
- Stability: stable in 3 of 3 calculated diagram(s): 300–1795.75 K, x(U) 0.25–0.25
- Literature: 0 values (0 accepted) from 0 papers
- Interactive: [phase registry entry](https://orchid-project.org/phases/#phase:si-u:si3u-l12)

Names (6): _corpus: _corpus:phase:si-u:si3u-l12  
_mp: _mp:mp-aaaaaeds  
_oqmd: _oqmd:oqmd-18109  
_tdb: _tdb:SiU-04Che-LB.tdb:SI3U_L12, tdb:SiU-09Ber.tdb:SI3U_L12, tdb:SiU-98AEA.tdb:SI3U_L12  


### TDB models of SI3U_L12 (3): PHASE and CONSTITUENT statements as written

[SiU-04Che-LB.tdb](https://orchid-project.org/data/databases/sgte-binary/SiU-04Che-LB.tdb): SI3U_L12, type code %, sha256 `84486566b19cb138…`

~~~~text
63: PHASE SI3U_L12 % 2 3 1 !
64: CONST SI3U_L12 : SI : U : !
~~~~

[SiU-09Ber.tdb](https://orchid-project.org/data/databases/sgte-binary/SiU-09Ber.tdb): SI3U_L12, type code %, sha256 `145f0a0d4b59bca1…`

~~~~text
57: PHASE SI3U_L12 % 2 3 1 !
58: CONST SI3U_L12 : SI : U : !
~~~~

[SiU-98AEA.tdb](https://orchid-project.org/data/databases/sgte-binary/SiU-98AEA.tdb): SI3U_L12, type code %, sha256 `ad20359bfb8262bf…`

~~~~text
64: PHASE SI3U_L12 % 2 3 1 !
65: CONST SI3U_L12 : SI : U : !
~~~~

Example references (1 of 1; assessments first): 

- [doi:10.1016/j.jnucmat.2009.01.014](https://doi.org/10.1016/j.jnucmat.2009.01.014) A. Berche, C. Rado, O. Rapaud, C. Guéneau, J. Rogez, Thermodynamic study of the U–Si system, Journal of Nuclear Materials 389, 101-107 (2009).  
_assessment that models this phase_

## SI5U3_C32 (Si–U)

- Id: `phase:si-u:si5u3-c32`; status `needs_review`
- No structure assigned. Why: assessment_declared_blocked_by:stoichiometry_contradicts_C32; stoichiometry_contradicts_C32:SiU-04Che-LB.tdb; stoichiometry_contradicts_C32:SiU-09Ber.tdb; stoichiometry_contradicts_C32:SiU-98AEA.tdb
- Candidate (name_token): AlB2 · C32 · hP3 · P6/mmm (191) — Strukturbericht/word 'C32' in the TDB name
- Candidate (sgte_mmc2): AlB2 · C32 · hP3 · P6/mmm (191) — Hallstedt 2025 mmc2 row for SI5U3_C32: Si5U3
- Candidate (tdb_comment): AlB2 · hP3 · P6/mmm — SiU-04Che-LB.tdb: 'Prototype AlB2 (hP3, P6/mmm)'
- Candidate (tdb_comment): AlB2 · hP3 · P6/mmm — SiU-09Ber.tdb: 'Prototype AlB2 (hP3, P6/mmm)'
- Candidate (tdb_comment): AlB2 · hP3 · P6/mmm — SiU-98AEA.tdb: 'Prototype AlB2 (hP3, P6/mmm)'
- Stoichiometry: Si 0.6250, U 0.3750
- Stability: stable in 3 of 3 calculated diagram(s): 300–2040.44 K, x(U) 0.375–0.375
- Literature: 0 values (0 accepted) from 0 papers
- Interactive: [phase registry entry](https://orchid-project.org/phases/#phase:si-u:si5u3-c32)

Names (4): _corpus: _corpus:phase:si-u:si5u3-c32  
_tdb: _tdb:SiU-04Che-LB.tdb:SI5U3_C32, tdb:SiU-09Ber.tdb:SI5U3_C32, tdb:SiU-98AEA.tdb:SI5U3_C32  


### TDB models of SI5U3_C32 (3): PHASE and CONSTITUENT statements as written

[SiU-04Che-LB.tdb](https://orchid-project.org/data/databases/sgte-binary/SiU-04Che-LB.tdb): SI5U3_C32, type code %, sha256 `84486566b19cb138…`

~~~~text
73: PHASE SI5U3_C32 % 2 5 3 !
74: CONST SI5U3_C32 : SI : U : !
~~~~

[SiU-09Ber.tdb](https://orchid-project.org/data/databases/sgte-binary/SiU-09Ber.tdb): SI5U3_C32, type code %, sha256 `145f0a0d4b59bca1…`

~~~~text
67: PHASE SI5U3_C32 % 2 5 3 !
68: CONST SI5U3_C32 : SI : U : !
~~~~

[SiU-98AEA.tdb](https://orchid-project.org/data/databases/sgte-binary/SiU-98AEA.tdb): SI5U3_C32, type code %, sha256 `ad20359bfb8262bf…`

~~~~text
74: PHASE SI5U3_C32 % 2 5 3 !
75: CONST SI5U3_C32 : SI : U : !
~~~~

Example references (1 of 1; assessments first): 

- [doi:10.1016/j.jnucmat.2009.01.014](https://doi.org/10.1016/j.jnucmat.2009.01.014) A. Berche, C. Rado, O. Rapaud, C. Guéneau, J. Rogez, Thermodynamic study of the U–Si system, Journal of Nuclear Materials 389, 101-107 (2009).  
_assessment that models this phase_

## SIU_B27 (Si–U)

- Id: `phase:si-u:siu-b27`; status `needs_review`
- No structure assigned. Why: assessment_declared_blocked_by:models_disagree_on_composition; models_disagree_on_composition; stoichiometry_contradicts_B27:SiU-04Che-LB.tdb; stoichiometry_contradicts_B27:SiU-09Ber.tdb
- Candidate (name_token): FeB · B27 · oP8 · Pnma (62) — Strukturbericht/word 'B27' in the TDB name
- Candidate (sgte_mmc2): FeB · B27 · oP8 · Pnma (62) — Hallstedt 2025 mmc2 row for SIU_B27: SiU
- Candidate (tdb_comment): FeB · oP8 · Pnma — SiU-04Che-LB.tdb: 'Prototype FeB (oP8, Pnma)'
- Candidate (tdb_comment): FeB · oP8 · Pnma — SiU-09Ber.tdb: 'Prototype FeB (oP8, Pnma)'
- Candidate (tdb_comment): FeB · oP8 · Pnma — SiU-98AEA.tdb: 'Prototype FeB (oP8, Pnma)'
- Stability: stable in 3 of 3 calculated diagram(s): 300–1871.05 K, x(U) 0.489–0.5
- Literature: 0 values (0 accepted) from 0 papers
- Interactive: [phase registry entry](https://orchid-project.org/phases/#phase:si-u:siu-b27)

Names (4): _corpus: _corpus:phase:si-u:siu-b27  
_tdb: _tdb:SiU-04Che-LB.tdb:SIU_B27, tdb:SiU-09Ber.tdb:SIU_B27, tdb:SiU-98AEA.tdb:SIU_B27  


### TDB models of SIU_B27 (3): PHASE and CONSTITUENT statements as written

[SiU-04Che-LB.tdb](https://orchid-project.org/data/databases/sgte-binary/SiU-04Che-LB.tdb): SIU_B27, type code %, sha256 `84486566b19cb138…`

~~~~text
78: PHASE SIU_B27 % 2 0.511 0.489 !
79: CONST SIU_B27 : SI : U : !
~~~~

[SiU-09Ber.tdb](https://orchid-project.org/data/databases/sgte-binary/SiU-09Ber.tdb): SIU_B27, type code %, sha256 `145f0a0d4b59bca1…`

~~~~text
72: PHASE SIU_B27 % 2 3.45 3.4 !
73: CONST SIU_B27 : SI : U : !
~~~~

[SiU-98AEA.tdb](https://orchid-project.org/data/databases/sgte-binary/SiU-98AEA.tdb): SIU_B27, type code %, sha256 `ad20359bfb8262bf…`

~~~~text
79: PHASE SIU_B27 % 2 1 1 !
80: CONST SIU_B27 : SI : U : !
~~~~

Example references (1 of 1; assessments first): 

- [doi:10.1016/j.jnucmat.2009.01.014](https://doi.org/10.1016/j.jnucmat.2009.01.014) A. Berche, C. Rado, O. Rapaud, C. Guéneau, J. Rogez, Thermodynamic study of the U–Si system, Journal of Nuclear Materials 389, 101-107 (2009).  
_assessment that models this phase_

## SIU3 (Si–U)

- Id: `phase:si-u:siu3`; status `needs_review`
- No structure assigned. Why: no_structure_token; polymorph_family:other phases of this system have the same composition
- Candidate (dft_mp): I4/mcm (140) — on-hull MP U3Si at x(U)=0.7500
- Candidate (dft_oqmd): I4/mcm (140) — on-hull OQMD Si1 U3 at x(U)=0.7500
- Candidate (tdb_comment): SiU3 · tI16 · I4/mcm — SiU-09Ber.tdb: 'Prototype SiU3 (tI16, I4/mcm), low T'
- Candidate (tdb_comment): SiU3 · tI16 · I4/mcm, D0_c — SiU-98AEA.tdb: 'Prototype SiU3 (tI16, I4/mcm, D0_c), low T'
- Stoichiometry: Si 0.2500, U 0.7500
- Stability: stable in 2 of 2 calculated diagram(s): 300–1205.16 K, x(U) 0.75–0.75
- Literature: 0 values (0 accepted) from 0 papers
- Interactive: [phase registry entry](https://orchid-project.org/phases/#phase:si-u:siu3)

Names (3): _corpus: _corpus:phase:si-u:siu3  
_tdb: _tdb:SiU-09Ber.tdb:SIU3, tdb:SiU-98AEA.tdb:SIU3  


### TDB models of SIU3 (2): PHASE and CONSTITUENT statements as written

[SiU-09Ber.tdb](https://orchid-project.org/data/databases/sgte-binary/SiU-09Ber.tdb): SIU3, type code %, sha256 `145f0a0d4b59bca1…`

~~~~text
83: PHASE SIU3 % 2 1 3 !
84: CONST SIU3 : SI : U : !
~~~~

[SiU-98AEA.tdb](https://orchid-project.org/data/databases/sgte-binary/SiU-98AEA.tdb): SIU3, type code %, sha256 `ad20359bfb8262bf…`

~~~~text
90: PHASE SIU3 % 2 1 3 !
91: CONST SIU3 : SI : U : !
~~~~

Example references (1 of 1; assessments first): 

- [doi:10.1016/j.jnucmat.2009.01.014](https://doi.org/10.1016/j.jnucmat.2009.01.014) A. Berche, C. Rado, O. Rapaud, C. Guéneau, J. Rogez, Thermodynamic study of the U–Si system, Journal of Nuclear Materials 389, 101-107 (2009).  
_assessment that models this phase_

## SIU3_D0C (Si–U)

- Id: `phase:si-u:siu3-d0c`; status `assigned`
- Structure: SiU3-lt · D0_c · tI16 · I4/mcm (140); type `st:d0-c-siu3-lt-ti16`; tier A: standard phase name; confidence high
- Stoichiometry: Si 0.2500, U 0.7500
- Stability: stable in 1 of 1 calculated diagram(s): 300–1260 K, x(U) 0.75–0.75
- Literature: 0 values (0 accepted) from 0 papers
- Interactive: [phase registry entry](https://orchid-project.org/phases/#phase:si-u:siu3-d0c)

Names (2): _corpus: _corpus:phase:si-u:siu3-d0c  
_tdb: _tdb:SiU-04Che-LB.tdb:SIU3_D0C  


### TDB models of SIU3_D0C (1): PHASE and CONSTITUENT statements as written

[SiU-04Che-LB.tdb](https://orchid-project.org/data/databases/sgte-binary/SiU-04Che-LB.tdb): SIU3_D0C, type code %, sha256 `84486566b19cb138…`

~~~~text
88: PHASE SIU3_D0C % 2 1 3 !
89: CONST SIU3_D0C : SI : U : !
~~~~

## SIU3_L12 (Si–U)

- Id: `phase:si-u:siu3-l12`; status `assigned`
- Structure: AuCu3 · L1_2 · cP4 · Pm-3m (221); type `st:l1-2-aucu3-cp4`; tier A: standard phase name; confidence high
- Stoichiometry: Si 0.2500, U 0.7500
- Stability: stable in 1 of 1 calculated diagram(s): 1037.98–1200 K, x(U) 0.75–0.75
- Literature: 0 values (0 accepted) from 0 papers
- Interactive: [phase registry entry](https://orchid-project.org/phases/#phase:si-u:siu3-l12)

Names (2): _corpus: _corpus:phase:si-u:siu3-l12  
_tdb: _tdb:SiU-04Che-LB.tdb:SIU3_L12  


### TDB models of SIU3_L12 (1): PHASE and CONSTITUENT statements as written

[SiU-04Che-LB.tdb](https://orchid-project.org/data/databases/sgte-binary/SiU-04Che-LB.tdb): SIU3_L12, type code %, sha256 `84486566b19cb138…`

~~~~text
93: PHASE SIU3_L12 % 2 1 3 !
94: CONST SIU3_L12 : SI : U : !
~~~~

## TETRAGONAL_U (Si–U)

- Id: `phase:si-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 — SiU-04Che-LB.tdb: 'Prototype beta-U (tP30, P4_2/mnm, SB: A_b)'
- Candidate (tdb_comment): beta-U · tP30 · P4_2/mnm, SB: A_b — SiU-09Ber.tdb: 'Prototype beta-U (tP30, P4_2/mnm, SB: A_b)'
- Candidate (tdb_comment): beta-U · tP30 · P4_2/mnm, SB: A_b — SiU-98AEA.tdb: 'Prototype beta-U (tP30, P4_2/mnm, SB: A_b)'
- Stability: stable in 3 of 3 calculated diagram(s): 920.82–1057.52 K, x(U) 0.98734–1
- Literature: 0 values (0 accepted) from 0 papers
- Interactive: [phase registry entry](https://orchid-project.org/phases/#phase:si-u:u-tetragonal)

Names (4): _corpus: _corpus:phase:si-u:u-tetragonal  
_tdb: _tdb:SiU-04Che-LB.tdb:TETRAGONAL_U, tdb:SiU-09Ber.tdb:TETRAGONAL_U, tdb:SiU-98AEA.tdb:TETRAGONAL_U  


### TDB models of TETRAGONAL_U (3): PHASE and CONSTITUENT statements as written

[SiU-04Che-LB.tdb](https://orchid-project.org/data/databases/sgte-binary/SiU-04Che-LB.tdb): TETRAGONAL_U, type code %, sha256 `84486566b19cb138…`

~~~~text
58: PHASE TETRAGONAL_U % 1 1 !
59: CONST TETRAGONAL_U : SI U% : !
~~~~

[SiU-09Ber.tdb](https://orchid-project.org/data/databases/sgte-binary/SiU-09Ber.tdb): TETRAGONAL_U, type code %, sha256 `145f0a0d4b59bca1…`

~~~~text
52: PHASE TETRAGONAL_U % 1 1 !
53: CONST TETRAGONAL_U : SI U% : !
~~~~

[SiU-98AEA.tdb](https://orchid-project.org/data/databases/sgte-binary/SiU-98AEA.tdb): TETRAGONAL_U, type code %, sha256 `ad20359bfb8262bf…`

~~~~text
59: PHASE TETRAGONAL_U % 1 1 !
60: CONST TETRAGONAL_U : U : !
~~~~

Example references (1 of 1; assessments first): 

- [doi:10.1016/j.jnucmat.2009.01.014](https://doi.org/10.1016/j.jnucmat.2009.01.014) A. Berche, C. Rado, O. Rapaud, C. Guéneau, J. Rogez, Thermodynamic study of the U–Si system, Journal of Nuclear Materials 389, 101-107 (2009).  
_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).