A transition that changes the state of a system which cannot be readily reversed to restore the system to its original state. Example: The conversion of
TiO2 (anatase) to
TiO2 (rutile).
Source:
PAC, 1994, 66, 577. 'Definitions of terms relating to phase transitions of the solid state (IUPAC Recommendations 1994)' on page 584 (https://doi.org/10.1351/pac199466030577)