# O–Si phases

> O–Si system: 17 phases (tier A 4, liquid 2, gas 2, needs_review 7, unresolved_no_candidates 2); 9 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/O-SI.html · Markdown: https://data.orchid-project.org/phases/pages/O-SI.md

17 phases (tier A 4, liquid 2, gas 2, needs_review 7, unresolved_no_candidates 2); 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](https://orchid-project.org/phases/?q=O-SI) · [full JSON](https://data.orchid-project.org/phases/systems/O-SI.json) · [O–Si system page](https://data.orchid-project.org/systems/O-SI.html) · [Markdown](https://data.orchid-project.org/phases/pages/O-SI.md) · [field reference](https://data.orchid-project.org/phases/SCHEMA.md)

Table: Phases of the O–Si system (17)

| Phase | Structure | Basis | Stability (calculated) | Literature values | TDB models |
|---|---|---|---|---:|---:|
| [A_CRISTOBALITE](#phase-o-si-a-cristobalite); _phase:o-si:a-cristobalite_ |  | needs_review | no calculated diagram | 0 | 1 |
| [A_QUARTZ](#phase-o-si-a-quartz); _phase:o-si:a-quartz_ |  | needs_review | no calculated diagram | 0 | 1 |
| [DIAMOND_A4](#phase-o-si-a4-diamond); _phase:o-si:a4-diamond_ | C (diamond) · A4 · cF8 · Fd-3m (227) | tier A: standard phase name | stable in 2 of 2 calculated diagram(s): 300–1687 K, x(O) 0–5e-05 | 1 | 3 |
| [B_CRISTOBALITE](#phase-o-si-b-cristobalite); _phase:o-si:b-cristobalite_ |  | needs_review | no calculated diagram | 0 | 1 |
| [B_QUARTZ](#phase-o-si-b-quartz); _phase:o-si:b-quartz_ |  | needs_review | no calculated diagram | 0 | 1 |
| [BCC_A2](#phase-o-si-bcc-a2); _phase:o-si:bcc-a2_ | W · A2 · cI2 · Im-3m (229) | tier A: standard phase name | not stable in 2 calculated diagram(s) | 0 | 3 |
| [CRISTOBALITE](#phase-o-si-cristobalite); _phase:o-si:cristobalite_ |  | needs_review | stable in 2 of 2 calculated diagram(s): 1145.12–1998 K, x(O) 0.66667–0.66667 | 2 | 2 |
| [FCC_A1](#phase-o-si-fcc-a1); _phase:o-si:fcc-a1_ | Cu · A1 · cF4 · Fm-3m (225) | tier A: standard phase name | not stable in 2 calculated diagram(s) | 0 | 3 |
| [GAS](#phase-o-si-gas); _phase:o-si:gas_ | gas | gas | stable in 2 of 2 calculated diagram(s): 300.12–2500 K, x(O) 0.49877–1 | 3 | 3 |
| [HCP_A3](#phase-o-si-hcp-a3); _phase:o-si:hcp-a3_ | Mg · A3 · hP2 · P6_3/mmc (194) | tier A: standard phase name | not stable in 2 calculated diagram(s) | 0 | 3 |
| [ION](#phase-o-si-ion); _phase:o-si:ion_ | liquid | liquid | stable in 1 of 1 calculated diagram(s): 1469.58–2500 K, x(O) 0–0.66667 | 0 | 1 |
| [LIQUID](#phase-o-si-liquid); _phase:o-si:liquid_ | liquid | liquid | stable in 2 of 2 calculated diagram(s): 1687–2500 K, x(O) 0–0.00064 | 3 | 3 |
| [O2GAS](#phase-o-si-o2gas); _phase:o-si:o2gas_ | gas | gas | stable in 2 of 2 calculated diagram(s): 300–1190.12 K, x(O) 1–1 | 0 | 3 |
| [QUARTZ](#phase-o-si-quartz); _phase:o-si:quartz_ |  | needs_review | stable in 2 of 2 calculated diagram(s): 300–1145.12 K, x(O) 0.66667–0.66667 | 0 | 2 |
| [SIO_AM](#phase-o-si-sio-am); _phase:o-si:sio-am_ |  | unresolved_no_candidates | not stable in 1 calculated diagram(s) | 0 | 1 |
| [SIO2_L](#phase-o-si-sio2-l); _phase:o-si:sio2-l_ |  | unresolved_no_candidates | stable in 1 of 1 calculated diagram(s): 1998–2500 K, x(O) 0.66667–0.66667 | 0 | 2 |
| [TRIDYMITE](#phase-o-si-tridymite); _phase:o-si:tridymite_ |  | needs_review | stable in 1 of 2 calculated diagram(s): 1143.04–1744.11 K, x(O) 0.66667–0.66667 | 1 | 2 |

## A_CRISTOBALITE (O–Si)

- Id: `phase:o-si:a-cristobalite`; status `needs_review`
- No structure assigned. Why: name_has_descriptive_tokens:A,CRISTOBALITE; no_structure_token
- Candidate (tdb_comment): SiO2 · tP12 · P4_12_12; low — SiO-20Baj-3g.tdb: 'Prototype SiO2 (tP12, P4_12_12; low)'
- Stability: no calculated diagram
- Literature: 0 values (0 accepted) from 0 papers
- Interactive: [phase registry entry](https://orchid-project.org/phases/#phase:o-si:a-cristobalite)

Names (2): _corpus: _corpus:phase:o-si:a-cristobalite  
_tdb: _tdb:SiO-20Baj-3g.tdb:A_CRISTOBALITE  


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

[SiO-20Baj-3g.tdb](https://orchid-project.org/data/databases/sgte-binary/SiO-20Baj-3g.tdb): A_CRISTOBALITE, type code %, sha256 `ad6c07bdbf4999c8…`

~~~~text
90: PHASE A_CRISTOBALITE % 1 1 !
91: CONST A_CRISTOBALITE : SIO2 : !
~~~~

Example references (1 of 1; assessments first): 

- [doi:10.1016/j.calphad.2019.101716](https://doi.org/10.1016/j.calphad.2019.101716) I. Bajenova, A. Khvan, A. Dinsdale, A. Kondratiev, Calphad, 68, 101716(2020).  
_assessment that models this phase_

## A_QUARTZ (O–Si)

- Id: `phase:o-si:a-quartz`; status `needs_review`
- No structure assigned. Why: name_has_descriptive_tokens:A,QUARTZ; no_structure_token
- Candidate (tdb_comment): SiO2 · hP9 · P3_121; alpha — SiO-20Baj-3g.tdb: 'Prototype SiO2 (hP9, P3_121; alpha)'
- Stability: no calculated diagram
- Literature: 0 values (0 accepted) from 0 papers
- Interactive: [phase registry entry](https://orchid-project.org/phases/#phase:o-si:a-quartz)

Names (2): _corpus: _corpus:phase:o-si:a-quartz  
_tdb: _tdb:SiO-20Baj-3g.tdb:A_QUARTZ  


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

[SiO-20Baj-3g.tdb](https://orchid-project.org/data/databases/sgte-binary/SiO-20Baj-3g.tdb): A_QUARTZ, type code %, sha256 `ad6c07bdbf4999c8…`

~~~~text
80: PHASE A_QUARTZ % 1 1 !
81: CONST A_QUARTZ : SIO2 : !
~~~~

Example references (1 of 1; assessments first): 

- [doi:10.1016/j.calphad.2019.101716](https://doi.org/10.1016/j.calphad.2019.101716) I. Bajenova, A. Khvan, A. Dinsdale, A. Kondratiev, Calphad, 68, 101716(2020).  
_assessment that models this phase_

## DIAMOND_A4 (O–Si)

- Id: `phase:o-si: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
- Stability: stable in 2 of 2 calculated diagram(s): 300–1687 K, x(O) 0–5e-05
- Literature: 1 values (1 accepted) from 1 papers
- Interactive: [phase registry entry](https://orchid-project.org/phases/#phase:o-si:a4-diamond)

Names (5): _corpus: _corpus:phase:o-si:a4-diamond  
_paper: _paper:10.1016/0364-5916(92)90038-y:(Si)  
_tdb: _tdb:SiO-04Sch.tdb:DIAMOND_A4, tdb:SiO-20Baj-3g.tdb:DIAMOND_A4, tdb:SiO-92Hal.tdb:DIAMOND_A4  


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

[SiO-04Sch.tdb](https://orchid-project.org/data/databases/sgte-binary/SiO-04Sch.tdb): DIAMOND_A4, type code %, sha256 `0f627cab998ca6d6…`

~~~~text
69: PHASE DIAMOND_A4 % 1 1 !
70: CONST DIAMOND_A4 : O SI : !
~~~~

[SiO-20Baj-3g.tdb](https://orchid-project.org/data/databases/sgte-binary/SiO-20Baj-3g.tdb): DIAMOND_A4, type code %, sha256 `ad6c07bdbf4999c8…`

~~~~text
70: PHASE DIAMOND_A4 % 1 1 !
71: CONST DIAMOND_A4 : O SI : !
~~~~

[SiO-92Hal.tdb](https://orchid-project.org/data/databases/sgte-binary/SiO-92Hal.tdb): DIAMOND_A4, type code %, sha256 `243e703636b34ae0…`

~~~~text
59: PHASE DIAMOND_A4 % 1 1 !
60: CONST DIAMOND_A4 : O SI : !
~~~~

Example references (3 of 3; assessments first): 

- [doi:10.1016/0364-5916(92)90038-Y](https://doi.org/10.1016/0364-5916%2892%2990038-Y) B. Hallstedt, Calphad, 16, 53-61(1992).  
_assessment that models this phase; reports values for this phase_
- [doi:10.1016/j.calphad.2019.101716](https://doi.org/10.1016/j.calphad.2019.101716) I. Bajenova, A. Khvan, A. Dinsdale, A. Kondratiev, Calphad, 68, 101716(2020).  
_assessment that models this phase_
- [doi:10.1016/j.jnoncrysol.2003.12.057](https://doi.org/10.1016/j.jnoncrysol.2003.12.057) S.M. Schnurre, J. Gröbner, R. Schmid-Fetzer, Thermodynamics and phase stability in the Si–O system, Journal of Non-Crystalline Solids 336, 1-25 (2004).  
_assessment that models this phase_

## B_CRISTOBALITE (O–Si)

- Id: `phase:o-si:b-cristobalite`; status `needs_review`
- No structure assigned. Why: name_has_descriptive_tokens:B,CRISTOBALITE; no_structure_token
- Candidate (tdb_comment): SiO2 · cF104 · Fd-3m, C9; beta — SiO-20Baj-3g.tdb: 'Prototype SiO2 (cF104, Fd-3m, C9; beta)'
- Stability: no calculated diagram
- Literature: 0 values (0 accepted) from 0 papers
- Interactive: [phase registry entry](https://orchid-project.org/phases/#phase:o-si:b-cristobalite)

Names (2): _corpus: _corpus:phase:o-si:b-cristobalite  
_tdb: _tdb:SiO-20Baj-3g.tdb:B_CRISTOBALITE  


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

[SiO-20Baj-3g.tdb](https://orchid-project.org/data/databases/sgte-binary/SiO-20Baj-3g.tdb): B_CRISTOBALITE, type code %, sha256 `ad6c07bdbf4999c8…`

~~~~text
95: PHASE B_CRISTOBALITE % 1 1 !
96: CONST B_CRISTOBALITE : SIO2 : !
~~~~

Example references (1 of 1; assessments first): 

- [doi:10.1016/j.calphad.2019.101716](https://doi.org/10.1016/j.calphad.2019.101716) I. Bajenova, A. Khvan, A. Dinsdale, A. Kondratiev, Calphad, 68, 101716(2020).  
_assessment that models this phase_

## B_QUARTZ (O–Si)

- Id: `phase:o-si:b-quartz`; status `needs_review`
- No structure assigned. Why: name_has_descriptive_tokens:B,QUARTZ; no_structure_token
- Candidate (tdb_comment): SiO2 · hP9 · P6_222, C8; beta — SiO-20Baj-3g.tdb: 'Prototype SiO2 (hP9, P6_222, C8; beta)'
- Stability: no calculated diagram
- Literature: 0 values (0 accepted) from 0 papers
- Interactive: [phase registry entry](https://orchid-project.org/phases/#phase:o-si:b-quartz)

Names (2): _corpus: _corpus:phase:o-si:b-quartz  
_tdb: _tdb:SiO-20Baj-3g.tdb:B_QUARTZ  


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

[SiO-20Baj-3g.tdb](https://orchid-project.org/data/databases/sgte-binary/SiO-20Baj-3g.tdb): B_QUARTZ, type code %, sha256 `ad6c07bdbf4999c8…`

~~~~text
85: PHASE B_QUARTZ % 1 1 !
86: CONST B_QUARTZ : SIO2 : !
~~~~

Example references (1 of 1; assessments first): 

- [doi:10.1016/j.calphad.2019.101716](https://doi.org/10.1016/j.calphad.2019.101716) I. Bajenova, A. Khvan, A. Dinsdale, A. Kondratiev, Calphad, 68, 101716(2020).  
_assessment that models this phase_

## BCC_A2 (O–Si)

- Id: `phase:o-si:bcc-a2`; status `assigned`
- Structure: W · A2 · cI2 · Im-3m (229); type `st:a2-w-ci2`; 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:o-si:bcc-a2)

Names (4): _corpus: _corpus:phase:o-si:bcc-a2  
_tdb: _tdb:SiO-04Sch.tdb:BCC_A2, tdb:SiO-20Baj-3g.tdb:BCC_A2, tdb:SiO-92Hal.tdb:BCC_A2  


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

[SiO-04Sch.tdb](https://orchid-project.org/data/databases/sgte-binary/SiO-04Sch.tdb): BCC_A2, type code %B, sha256 `0f627cab998ca6d6…`

~~~~text
59: PHASE BCC_A2 %B 2 1 3 !
60: CONST BCC_A2 : SI : O VA% : !
~~~~

[SiO-20Baj-3g.tdb](https://orchid-project.org/data/databases/sgte-binary/SiO-20Baj-3g.tdb): BCC_A2, type code %B, sha256 `ad6c07bdbf4999c8…`

~~~~text
60: PHASE BCC_A2 %B 2 1 3 !
61: CONST BCC_A2 : SI : O VA% : !
~~~~

[SiO-92Hal.tdb](https://orchid-project.org/data/databases/sgte-binary/SiO-92Hal.tdb): BCC_A2, type code %B, sha256 `243e703636b34ae0…`

~~~~text
49: PHASE BCC_A2 %B 2 1 3 !
50: CONST BCC_A2 : SI : O VA% : !
~~~~

Example references (3 of 3; assessments first): 

- [doi:10.1016/0364-5916(92)90038-Y](https://doi.org/10.1016/0364-5916%2892%2990038-Y) B. Hallstedt, Calphad, 16, 53-61(1992).  
_assessment that models this phase_
- [doi:10.1016/j.calphad.2019.101716](https://doi.org/10.1016/j.calphad.2019.101716) I. Bajenova, A. Khvan, A. Dinsdale, A. Kondratiev, Calphad, 68, 101716(2020).  
_assessment that models this phase_
- [doi:10.1016/j.jnoncrysol.2003.12.057](https://doi.org/10.1016/j.jnoncrysol.2003.12.057) S.M. Schnurre, J. Gröbner, R. Schmid-Fetzer, Thermodynamics and phase stability in the Si–O system, Journal of Non-Crystalline Solids 336, 1-25 (2004).  
_assessment that models this phase_

## CRISTOBALITE (O–Si)

- Id: `phase:o-si:cristobalite`; status `needs_review`
- No structure assigned. Why: name_has_descriptive_tokens:CRISTOBALITE; no_structure_token; sgte_mmc2_rows_disagree
- Candidate (sgte_mmc2): SiO2 · C9 · cF24 · Fd-3m (227) — Hallstedt 2025 mmc2 row for CRISTOBALITE: SiO2 (beta cristobalite)
- Candidate (sgte_mmc2): SiO2 · tP12 · P4_12_12 (92) — Hallstedt 2025 mmc2 row for CRISTOBALITE: SiO2 (low cristobalite)
- Candidate (tdb_comment): SiO2 · cF104 · Fd-3m, C9; beta and tP12, P4_12_12; low — SiO-04Sch.tdb: 'Prototype SiO2 (cF104, Fd-3m, C9; beta and tP12, P4_12_12; low)'
- Candidate (tdb_comment): SiO2 · cF104 · Fd-3m, C9; beta and tP12, P4_12_12; low — SiO-92Hal.tdb: 'Prototype SiO2 (cF104, Fd-3m, C9; beta and tP12, P4_12_12; low)'
- Stability: stable in 2 of 2 calculated diagram(s): 1145.12–1998 K, x(O) 0.66667–0.66667
- Literature: 2 values (1 accepted) from 2 papers
- Interactive: [phase registry entry](https://orchid-project.org/phases/#phase:o-si:cristobalite)

Names (5): _corpus: _corpus:phase:o-si:cristobalite  
_paper: _paper:10.1016/0364-5916(92)90038-y:Cristobalite, paper:10.1016/j.jnoncrysol.2003.12.057:cristobalite  
_tdb: _tdb:SiO-04Sch.tdb:CRISTOBALITE, tdb:SiO-92Hal.tdb:CRISTOBALITE  


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

[SiO-04Sch.tdb](https://orchid-project.org/data/databases/sgte-binary/SiO-04Sch.tdb): CRISTOBALITE, type code %, sha256 `0f627cab998ca6d6…`

~~~~text
89: PHASE CRISTOBALITE % 1 1 !
90: CONST CRISTOBALITE : SIO2 : !
~~~~

[SiO-92Hal.tdb](https://orchid-project.org/data/databases/sgte-binary/SiO-92Hal.tdb): CRISTOBALITE, type code %, sha256 `243e703636b34ae0…`

~~~~text
64: PHASE CRISTOBALITE % 1 1 !
65: CONST CRISTOBALITE : SIO2 : !
~~~~

Example references (2 of 2; assessments first): 

- [doi:10.1016/0364-5916(92)90038-Y](https://doi.org/10.1016/0364-5916%2892%2990038-Y) B. Hallstedt, Calphad, 16, 53-61(1992).  
_assessment that models this phase; reports values for this phase_
- [doi:10.1016/j.jnoncrysol.2003.12.057](https://doi.org/10.1016/j.jnoncrysol.2003.12.057) S.M. Schnurre, J. Gröbner, R. Schmid-Fetzer, Thermodynamics and phase stability in the Si–O system, Journal of Non-Crystalline Solids 336, 1-25 (2004).  
_assessment that models this phase; reports values for this phase_

## FCC_A1 (O–Si)

- Id: `phase:o-si: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:o-si:fcc-a1)

Names (4): _corpus: _corpus:phase:o-si:fcc-a1  
_tdb: _tdb:SiO-04Sch.tdb:FCC_A1, tdb:SiO-20Baj-3g.tdb:FCC_A1, tdb:SiO-92Hal.tdb:FCC_A1  


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

[SiO-04Sch.tdb](https://orchid-project.org/data/databases/sgte-binary/SiO-04Sch.tdb): FCC_A1, type code %A, sha256 `0f627cab998ca6d6…`

~~~~text
54: PHASE FCC_A1 %A 2 1 1 !
55: CONST FCC_A1 : SI : O VA% : !
~~~~

[SiO-20Baj-3g.tdb](https://orchid-project.org/data/databases/sgte-binary/SiO-20Baj-3g.tdb): FCC_A1, type code %A, sha256 `ad6c07bdbf4999c8…`

~~~~text
55: PHASE FCC_A1 %A 2 1 1 !
56: CONST FCC_A1 : SI : O VA% : !
~~~~

[SiO-92Hal.tdb](https://orchid-project.org/data/databases/sgte-binary/SiO-92Hal.tdb): FCC_A1, type code %A, sha256 `243e703636b34ae0…`

~~~~text
44: PHASE FCC_A1 %A 2 1 1 !
45: CONST FCC_A1 : SI : O VA% : !
~~~~

Example references (3 of 3; assessments first): 

- [doi:10.1016/0364-5916(92)90038-Y](https://doi.org/10.1016/0364-5916%2892%2990038-Y) B. Hallstedt, Calphad, 16, 53-61(1992).  
_assessment that models this phase_
- [doi:10.1016/j.calphad.2019.101716](https://doi.org/10.1016/j.calphad.2019.101716) I. Bajenova, A. Khvan, A. Dinsdale, A. Kondratiev, Calphad, 68, 101716(2020).  
_assessment that models this phase_
- [doi:10.1016/j.jnoncrysol.2003.12.057](https://doi.org/10.1016/j.jnoncrysol.2003.12.057) S.M. Schnurre, J. Gröbner, R. Schmid-Fetzer, Thermodynamics and phase stability in the Si–O system, Journal of Non-Crystalline Solids 336, 1-25 (2004).  
_assessment that models this phase_

## GAS (O–Si)

- Id: `phase:o-si:gas`; status `assigned`
- Structure: gas; type `st:gas`; gas; confidence high
- Stability: stable in 2 of 2 calculated diagram(s): 300.12–2500 K, x(O) 0.49877–1
- Literature: 3 values (1 accepted) from 2 papers
- Interactive: [phase registry entry](https://orchid-project.org/phases/#phase:o-si:gas)

Names (6): _corpus: _corpus:phase:o-si:gas  
_paper: _paper:10.1016/0364-5916(92)90038-y:Gas, paper:10.1016/j.jnoncrysol.2003.12.057:gas  
_tdb: _tdb:SiO-04Sch.tdb:GAS, tdb:SiO-20Baj-3g.tdb:GAS, tdb:SiO-92Hal.tdb:GAS  


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

[SiO-04Sch.tdb](https://orchid-project.org/data/databases/sgte-binary/SiO-04Sch.tdb): GAS, type code %, sha256 `0f627cab998ca6d6…`

~~~~text
101: PHASE GAS:G % 1 1 !
102: CONST GAS:G : O O2 O3 SI SI2 SI3 SIO SIO2 : !
~~~~

[SiO-20Baj-3g.tdb](https://orchid-project.org/data/databases/sgte-binary/SiO-20Baj-3g.tdb): GAS, type code %, sha256 `ad6c07bdbf4999c8…`

~~~~text
101: PHASE GAS:G % 1 1 !
102: CONST GAS:G : O O2 O3 SI SI2 SI3 SIO SIO2 : !
~~~~

[SiO-92Hal.tdb](https://orchid-project.org/data/databases/sgte-binary/SiO-92Hal.tdb): GAS, type code %, sha256 `243e703636b34ae0…`

~~~~text
81: PHASE GAS:G % 1 1 !
82: CONST GAS:G : O O2 O3 SI SI2 SI3 SIO SIO2 : !
~~~~

Example references (3 of 3; assessments first): 

- [doi:10.1016/j.jnoncrysol.2003.12.057](https://doi.org/10.1016/j.jnoncrysol.2003.12.057) S.M. Schnurre, J. Gröbner, R. Schmid-Fetzer, Thermodynamics and phase stability in the Si–O system, Journal of Non-Crystalline Solids 336, 1-25 (2004).  
_assessment that models this phase; reports values for this phase_
- [doi:10.1016/0364-5916(92)90038-Y](https://doi.org/10.1016/0364-5916%2892%2990038-Y) B. Hallstedt, Calphad, 16, 53-61(1992).  
_assessment that models this phase; reports values for this phase_
- [doi:10.1016/j.calphad.2019.101716](https://doi.org/10.1016/j.calphad.2019.101716) I. Bajenova, A. Khvan, A. Dinsdale, A. Kondratiev, Calphad, 68, 101716(2020).  
_assessment that models this phase_

## HCP_A3 (O–Si)

- Id: `phase:o-si: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:o-si:hcp-a3)

Names (4): _corpus: _corpus:phase:o-si:hcp-a3  
_tdb: _tdb:SiO-04Sch.tdb:HCP_A3, tdb:SiO-20Baj-3g.tdb:HCP_A3, tdb:SiO-92Hal.tdb:HCP_A3  


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

[SiO-04Sch.tdb](https://orchid-project.org/data/databases/sgte-binary/SiO-04Sch.tdb): HCP_A3, type code %, sha256 `0f627cab998ca6d6…`

~~~~text
64: PHASE HCP_A3 % 2 1 0.5 !
65: CONST HCP_A3 : SI : O VA% : !
~~~~

[SiO-20Baj-3g.tdb](https://orchid-project.org/data/databases/sgte-binary/SiO-20Baj-3g.tdb): HCP_A3, type code %, sha256 `ad6c07bdbf4999c8…`

~~~~text
65: PHASE HCP_A3 % 2 1 0.5 !
66: CONST HCP_A3 : SI : O VA% : !
~~~~

[SiO-92Hal.tdb](https://orchid-project.org/data/databases/sgte-binary/SiO-92Hal.tdb): HCP_A3, type code %, sha256 `243e703636b34ae0…`

~~~~text
54: PHASE HCP_A3 % 2 1 0.5 !
55: CONST HCP_A3 : SI : O VA% : !
~~~~

Example references (3 of 3; assessments first): 

- [doi:10.1016/0364-5916(92)90038-Y](https://doi.org/10.1016/0364-5916%2892%2990038-Y) B. Hallstedt, Calphad, 16, 53-61(1992).  
_assessment that models this phase_
- [doi:10.1016/j.calphad.2019.101716](https://doi.org/10.1016/j.calphad.2019.101716) I. Bajenova, A. Khvan, A. Dinsdale, A. Kondratiev, Calphad, 68, 101716(2020).  
_assessment that models this phase_
- [doi:10.1016/j.jnoncrysol.2003.12.057](https://doi.org/10.1016/j.jnoncrysol.2003.12.057) S.M. Schnurre, J. Gröbner, R. Schmid-Fetzer, Thermodynamics and phase stability in the Si–O system, Journal of Non-Crystalline Solids 336, 1-25 (2004).  
_assessment that models this phase_

## ION (O–Si)

- Id: `phase:o-si:ion`; status `assigned`
- Structure: liquid; type `st:liquid`; liquid; confidence high
- Stability: stable in 1 of 1 calculated diagram(s): 1469.58–2500 K, x(O) 0–0.66667
- Literature: 0 values (0 accepted) from 0 papers
- Interactive: [phase registry entry](https://orchid-project.org/phases/#phase:o-si:ion)

Names (2): _corpus: _corpus:phase:o-si:ion  
_tdb: _tdb:SiO-92Hal.tdb:ION  


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

[SiO-92Hal.tdb](https://orchid-project.org/data/databases/sgte-binary/SiO-92Hal.tdb): ION, type code %, sha256 `243e703636b34ae0…`

~~~~text
39: PHASE ION:Y % 2 1 1 !
40: CONST ION:Y : SI+4 : O-2 VA SIO2 : !
~~~~

Example references (1 of 1; assessments first): 

- [doi:10.1016/0364-5916(92)90038-Y](https://doi.org/10.1016/0364-5916%2892%2990038-Y) B. Hallstedt, Calphad, 16, 53-61(1992).  
_assessment that models this phase_

## LIQUID (O–Si)

- Id: `phase:o-si:liquid`; status `assigned`
- Structure: liquid; type `st:liquid`; liquid; confidence high
- Stability: stable in 2 of 2 calculated diagram(s): 1687–2500 K, x(O) 0–0.00064
- Literature: 3 values (1 accepted) from 2 papers
- Interactive: [phase registry entry](https://orchid-project.org/phases/#phase:o-si:liquid)

Names (6): _corpus: _corpus:phase:o-si:liquid  
_paper: _paper:10.1016/0364-5916(92)90038-y:L1, paper:10.1016/j.jnoncrysol.2003.12.057:liquid  
_tdb: _tdb:SiO-04Sch.tdb:LIQUID, tdb:SiO-20Baj-3g.tdb:LIQUID, tdb:SiO-92Hal.tdb:LIQUID  


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

[SiO-04Sch.tdb](https://orchid-project.org/data/databases/sgte-binary/SiO-04Sch.tdb): LIQUID, type code %, sha256 `0f627cab998ca6d6…`

~~~~text
46: PHASE LIQUID:L % 1 1 !
47: CONST LIQUID:L : O SI : !
~~~~

[SiO-20Baj-3g.tdb](https://orchid-project.org/data/databases/sgte-binary/SiO-20Baj-3g.tdb): LIQUID, type code %, sha256 `ad6c07bdbf4999c8…`

~~~~text
47: PHASE LIQUID:L % 1 1 !
48: CONST LIQUID:L : O SI : !
~~~~

[SiO-92Hal.tdb](https://orchid-project.org/data/databases/sgte-binary/SiO-92Hal.tdb): LIQUID, type code %, sha256 `243e703636b34ae0…`

~~~~text
36: PHASE LIQUID:L % 1 1 !
37: CONST LIQUID:L : SI : !
~~~~

Example references (3 of 3; assessments first): 

- [doi:10.1016/j.jnoncrysol.2003.12.057](https://doi.org/10.1016/j.jnoncrysol.2003.12.057) S.M. Schnurre, J. Gröbner, R. Schmid-Fetzer, Thermodynamics and phase stability in the Si–O system, Journal of Non-Crystalline Solids 336, 1-25 (2004).  
_assessment that models this phase; reports values for this phase_
- [doi:10.1016/0364-5916(92)90038-Y](https://doi.org/10.1016/0364-5916%2892%2990038-Y) B. Hallstedt, Calphad, 16, 53-61(1992).  
_assessment that models this phase; reports values for this phase_
- [doi:10.1016/j.calphad.2019.101716](https://doi.org/10.1016/j.calphad.2019.101716) I. Bajenova, A. Khvan, A. Dinsdale, A. Kondratiev, Calphad, 68, 101716(2020).  
_assessment that models this phase_

## O2GAS (O–Si)

- Id: `phase:o-si:o2gas`; status `assigned`
- Structure: gas; type `st:gas`; gas; confidence high
- Stability: stable in 2 of 2 calculated diagram(s): 300–1190.12 K, x(O) 1–1
- Literature: 0 values (0 accepted) from 0 papers
- Interactive: [phase registry entry](https://orchid-project.org/phases/#phase:o-si:o2gas)

Names (4): _corpus: _corpus:phase:o-si:o2gas  
_tdb: _tdb:SiO-04Sch.tdb:O2GAS, tdb:SiO-20Baj-3g.tdb:O2GAS, tdb:SiO-92Hal.tdb:O2GAS  


### TDB models of O2GAS (3): PHASE and CONSTITUENT statements as written

[SiO-04Sch.tdb](https://orchid-project.org/data/databases/sgte-binary/SiO-04Sch.tdb): O2GAS, type code %, sha256 `0f627cab998ca6d6…`

~~~~text
98: PHASE O2GAS % 1 1 !
99: CONST O2GAS : O2 :!
~~~~

[SiO-20Baj-3g.tdb](https://orchid-project.org/data/databases/sgte-binary/SiO-20Baj-3g.tdb): O2GAS, type code %, sha256 `ad6c07bdbf4999c8…`

~~~~text
98: PHASE O2GAS % 1 1 !
99: CONST O2GAS : O2 :!
~~~~

[SiO-92Hal.tdb](https://orchid-project.org/data/databases/sgte-binary/SiO-92Hal.tdb): O2GAS, type code %, sha256 `243e703636b34ae0…`

~~~~text
78: PHASE O2GAS % 1 1 !
79: CONST O2GAS : O2 :!
~~~~

Example references (3 of 3; assessments first): 

- [doi:10.1016/0364-5916(92)90038-Y](https://doi.org/10.1016/0364-5916%2892%2990038-Y) B. Hallstedt, Calphad, 16, 53-61(1992).  
_assessment that models this phase_
- [doi:10.1016/j.calphad.2019.101716](https://doi.org/10.1016/j.calphad.2019.101716) I. Bajenova, A. Khvan, A. Dinsdale, A. Kondratiev, Calphad, 68, 101716(2020).  
_assessment that models this phase_
- [doi:10.1016/j.jnoncrysol.2003.12.057](https://doi.org/10.1016/j.jnoncrysol.2003.12.057) S.M. Schnurre, J. Gröbner, R. Schmid-Fetzer, Thermodynamics and phase stability in the Si–O system, Journal of Non-Crystalline Solids 336, 1-25 (2004).  
_assessment that models this phase_

## QUARTZ (O–Si)

- Id: `phase:o-si:quartz`; status `needs_review`
- No structure assigned. Why: name_has_descriptive_tokens:QUARTZ; no_structure_token; sgte_mmc2_rows_disagree
- Candidate (sgte_mmc2): SiO2 · C8 · hP9 · P6_222 (180) — Hallstedt 2025 mmc2 row for QUARTZ: SiO2 (beta quartz)
- Candidate (sgte_mmc2): SiO2 · hP9 · P3_121 (152) — Hallstedt 2025 mmc2 row for QUARTZ: SiO2 (alpha quartz)
- Candidate (tdb_comment): SiO2 · hP9 · P3_121; alpha and hP9, P6_222, C8; beta — SiO-04Sch.tdb: 'Prototype SiO2 (hP9, P3_121; alpha and hP9, P6_222, C8; beta)'
- Candidate (tdb_comment): SiO2 · hP9 · P3_121; alpha and hP9, P6_222, C8; beta — SiO-92Hal.tdb: 'Prototype SiO2 (hP9, P3_121; alpha and hP9, P6_222, C8; beta)'
- Stability: stable in 2 of 2 calculated diagram(s): 300–1145.12 K, x(O) 0.66667–0.66667
- Literature: 0 values (0 accepted) from 0 papers
- Interactive: [phase registry entry](https://orchid-project.org/phases/#phase:o-si:quartz)

Names (3): _corpus: _corpus:phase:o-si:quartz  
_tdb: _tdb:SiO-04Sch.tdb:QUARTZ, tdb:SiO-92Hal.tdb:QUARTZ  


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

[SiO-04Sch.tdb](https://orchid-project.org/data/databases/sgte-binary/SiO-04Sch.tdb): QUARTZ, type code %, sha256 `0f627cab998ca6d6…`

~~~~text
84: PHASE QUARTZ % 1 1 !
85: CONST QUARTZ : SIO2 : !
~~~~

[SiO-92Hal.tdb](https://orchid-project.org/data/databases/sgte-binary/SiO-92Hal.tdb): QUARTZ, type code %, sha256 `243e703636b34ae0…`

~~~~text
69: PHASE QUARTZ % 1 1 !
70: CONST QUARTZ : SIO2 : !
~~~~

Example references (2 of 2; assessments first): 

- [doi:10.1016/0364-5916(92)90038-Y](https://doi.org/10.1016/0364-5916%2892%2990038-Y) B. Hallstedt, Calphad, 16, 53-61(1992).  
_assessment that models this phase_
- [doi:10.1016/j.jnoncrysol.2003.12.057](https://doi.org/10.1016/j.jnoncrysol.2003.12.057) S.M. Schnurre, J. Gröbner, R. Schmid-Fetzer, Thermodynamics and phase stability in the Si–O system, Journal of Non-Crystalline Solids 336, 1-25 (2004).  
_assessment that models this phase_

## SIO_AM (O–Si)

- Id: `phase:o-si:sio-am`; status `unresolved_no_candidates`
- No structure assigned. Why: name_has_descriptive_tokens:AM; no_structure_token
- Stability: not stable in 1 calculated diagram(s)
- Literature: 0 values (0 accepted) from 0 papers
- Interactive: [phase registry entry](https://orchid-project.org/phases/#phase:o-si:sio-am)

Names (2): _corpus: _corpus:phase:o-si:sio-am  
_tdb: _tdb:SiO-04Sch.tdb:SIO_AM  


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

[SiO-04Sch.tdb](https://orchid-project.org/data/databases/sgte-binary/SiO-04Sch.tdb): SIO_AM, type code %, sha256 `0f627cab998ca6d6…`

~~~~text
74: PHASE SIO_AM % 1 1 !
75: CONST SIO_AM : SIO : !
~~~~

Example references (1 of 1; assessments first): 

- [doi:10.1016/j.jnoncrysol.2003.12.057](https://doi.org/10.1016/j.jnoncrysol.2003.12.057) S.M. Schnurre, J. Gröbner, R. Schmid-Fetzer, Thermodynamics and phase stability in the Si–O system, Journal of Non-Crystalline Solids 336, 1-25 (2004).  
_assessment that models this phase_

## SIO2_L (O–Si)

- Id: `phase:o-si:sio2-l`; status `unresolved_no_candidates`
- No structure assigned. Why: name_has_descriptive_tokens:L; no_structure_token
- Stability: stable in 1 of 1 calculated diagram(s): 1998–2500 K, x(O) 0.66667–0.66667
- Literature: 0 values (0 accepted) from 0 papers
- Interactive: [phase registry entry](https://orchid-project.org/phases/#phase:o-si:sio2-l)

Names (3): _corpus: _corpus:phase:o-si:sio2-l  
_tdb: _tdb:SiO-04Sch.tdb:SIO2_L, tdb:SiO-20Baj-3g.tdb:SIO2_L  


### TDB models of SIO2_L (2): PHASE and CONSTITUENT statements as written

[SiO-04Sch.tdb](https://orchid-project.org/data/databases/sgte-binary/SiO-04Sch.tdb): SIO2_L, type code %, sha256 `0f627cab998ca6d6…`

~~~~text
79: PHASE SIO2_L % 1 1 !
80: CONST SIO2_L : SIO2 : !
~~~~

[SiO-20Baj-3g.tdb](https://orchid-project.org/data/databases/sgte-binary/SiO-20Baj-3g.tdb): SIO2_L, type code %, sha256 `ad6c07bdbf4999c8…`

~~~~text
75: PHASE SIO2_L % 1 1 !
76: CONST SIO2_L : SIO2 : !
~~~~

Example references (2 of 2; assessments first): 

- [doi:10.1016/j.calphad.2019.101716](https://doi.org/10.1016/j.calphad.2019.101716) I. Bajenova, A. Khvan, A. Dinsdale, A. Kondratiev, Calphad, 68, 101716(2020).  
_assessment that models this phase_
- [doi:10.1016/j.jnoncrysol.2003.12.057](https://doi.org/10.1016/j.jnoncrysol.2003.12.057) S.M. Schnurre, J. Gröbner, R. Schmid-Fetzer, Thermodynamics and phase stability in the Si–O system, Journal of Non-Crystalline Solids 336, 1-25 (2004).  
_assessment that models this phase_

## TRIDYMITE (O–Si)

- Id: `phase:o-si:tridymite`; status `needs_review`
- No structure assigned. Why: name_has_descriptive_tokens:TRIDYMITE; no_structure_token; sgte_mmc2_rows_disagree
- Candidate (literature_printed): SiO2 · mC144 — printed with a label mapped to this phase
- Candidate (sgte_mmc2): SiO2 · C10 · hP12 · P6_3/mmc (194) — Hallstedt 2025 mmc2 row for TRIDYMITE: SiO2 (beta tridymite)
- Candidate (sgte_mmc2): SiO2 · mC144 · Cc (9) — Hallstedt 2025 mmc2 row for TRIDYMITE: SiO2 (low tridymite)
- Candidate (sgte_mmc2): SiO2 · oC24 · C222_1 (20) — Hallstedt 2025 mmc2 row for TRIDYMITE: SiO2 (high or ortho-I tridymite)
- Candidate (tdb_comment):  — SiO-04Sch.tdb: 'Prototype SiO2 (mC144, Cc; low and hP12, P6_3/mmc, C10; beta'
- Candidate (tdb_comment):  — SiO-92Hal.tdb: 'Prototype SiO2 (mC144, Cc; low and hP12, P6_3/mmc, C10; beta'
- Stability: stable in 1 of 2 calculated diagram(s): 1143.04–1744.11 K, x(O) 0.66667–0.66667
- Literature: 1 values (1 accepted) from 1 papers
- Interactive: [phase registry entry](https://orchid-project.org/phases/#phase:o-si:tridymite)

Names (4): _corpus: _corpus:phase:o-si:tridymite  
_paper: _paper:10.1016/0364-5916(92)90038-y:Tridymite  
_tdb: _tdb:SiO-04Sch.tdb:TRIDYMITE, tdb:SiO-92Hal.tdb:TRIDYMITE  


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

[SiO-04Sch.tdb](https://orchid-project.org/data/databases/sgte-binary/SiO-04Sch.tdb): TRIDYMITE, type code %, sha256 `0f627cab998ca6d6…`

~~~~text
95: PHASE TRIDYMITE % 1 1 !
96: CONST TRIDYMITE : SIO2 : !
~~~~

[SiO-92Hal.tdb](https://orchid-project.org/data/databases/sgte-binary/SiO-92Hal.tdb): TRIDYMITE, type code %, sha256 `243e703636b34ae0…`

~~~~text
75: PHASE TRIDYMITE % 1 1 !
76: CONST TRIDYMITE : SIO2 : !
~~~~

Example references (2 of 2; assessments first): 

- [doi:10.1016/0364-5916(92)90038-Y](https://doi.org/10.1016/0364-5916%2892%2990038-Y) B. Hallstedt, Calphad, 16, 53-61(1992).  
_assessment that models this phase; reports values for this phase_
- [doi:10.1016/j.jnoncrysol.2003.12.057](https://doi.org/10.1016/j.jnoncrysol.2003.12.057) S.M. Schnurre, J. Gröbner, R. Schmid-Fetzer, Thermodynamics and phase stability in the Si–O system, Journal of Non-Crystalline Solids 336, 1-25 (2004).  
_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).