An electron-ordering transition occurring in a mixed-valent system that results in an ordering of formal valence states in the low-temperature phase. Example: The prototype system, first identified by Verwey, is the ferrospinel magnetite, Fe3+[Fe3+Fe2+]O4
in which an ordering of Fe3+
ions within octahedral sites is thought to occur below T v ≈ 120 K.
PAC, 1994, 66, 577. 'Definitions of terms relating to phase transitions of the solid state (IUPAC Recommendations 1994)' on page 593 (https://doi.org/10.1351/pac199466030577)