Title: polymorphic transition
Long Title: IUPAC Gold Book - polymorphic transition
DOI: 10.1351/goldbook.P04748
Status: current

Definition
A reversible transition of a solid crystalline phase at a certain temperature and pressure (the inversion point) to another phase of the same chemical composition with a different crystal structure.

Note
In a liquid-crystal transition, this term refers to phase changes in the smectic state or columnar discotic state.

Examples
1) The transitions of $\ce{SiO2}$ (quartz-type) at \(1143\ \rm{K}\) to $\ce{SiO2}$ (tridymite-type), and at \(1743\ \rm{K}\) to $\ce{SiO2}$ (cristobalite-type).
2) The transition of $\ce{\upbeta\mbox{-}AgI}$ (wurtzite-type structure) to $\ce{\upalpha\mbox{-}AgI}$ (body-centred-cubic structure) at \(418\ \rm{K}\). Synonymous with 'enantiotropic transition'.


Related Terms
- enantiotropic transition: https://goldbook.iupac.org//terms/view/E02084
- inversion point: https://goldbook.iupac.org//terms/view/I03149
- reversible transition: https://goldbook.iupac.org//terms/view/R05379
- smectic state: https://goldbook.iupac.org//terms/view/S05714

Source
- PAC, 1994, 66, 577. 'Definitions of terms relating to phase transitions of the solid state (IUPAC Recommendations 1994)' on page 588 (https://doi.org/10.1351/pac199466030577)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/P04748/html
- json: https://goldbook.iupac.org/terms/view/P04748/json
- xml: https://goldbook.iupac.org/terms/view/P04748/xml

Citation: Citation: 'polymorphic transition' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351/goldbook.P04748
License: The IUPAC Gold Book is licensed under Creative Commons Attribution-ShareAlike CC BY-SA 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) for individual terms.
Collection: If you are interested in licensing the Gold Book for commercial use, please contact the IUPAC Executive Director at executivedirector@iupac.org .
Disclaimer: The International Union of Pure and Applied Chemistry (IUPAC) is continuously reviewing and, where needed, updating terms in the Compendium of Chemical Terminology (the IUPAC Gold Book). Users of these terms are encouraged to include the version of a term with its use and to check regularly for updates to term definitions that you are using.
Accessed: 2026-04-18T18:05:05+00:00