Term: polymorphic transition
https://doi.org/10.1351/goldbook.P04748

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. Examples:   The transitions of SiO2 (quartz-type) at 1143 K to SiO2 (tridymite-type), and at 1743 K to SiO2 (cristobalite-type).   The transition of β-AgI (wurtzite-type structure) to α-AgI (body-centred-cubic structure) at 418 K. Synonymous with enantiotropic transition.  

Note: In a liquid-crystal transition, this term refers to phase changes in the @S05714@ or columnar discotic state.

Related Terms:
1) reversible transition (http://doi.org/10.1351/goldbook.R05379).
2) inversion point (<em>in phase transitions</em>) (http://doi.org/10.1351/goldbook.I03149).
3) smectic state (<em>in phase transitions</em>) (http://doi.org/10.1351/goldbook.S05714).
4) enantiotropic transition (<em>in phase transitions</em>) (http://doi.org/10.1351/goldbook.E02084).

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)

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. https://doi.org/10.1351/goldbook.P04748

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