A transition in which the degree of order of the system changes. Three principal types
of disordering transitions may be distinguished: (i) positional disordering in a solid,
(ii) orientational disordering which may be static or dynamic and (iii) disordering
associated with electronic and nuclear spin states.
The transition of
LiFeO2, with a tetragonal unit cell, in which the
cations are perfectly ordered on crystallographically non-equivalent octahedral sites
LiFeO2 in which the
Fe3+ cations are distributed randomly over all the octahedral sites.
The transition of orthorhombic
KCN to cubic
KCN in which the
CN− ions become oriented in any of the eight  directions.
A superconducting transition
PAC, 1994, 66, 577
(Definitions of terms relating to phase transitions of the solid state (IUPAC Recommendations
on page 587
IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by
A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997).
XML on-line corrected version: http://goldbook.iupac.org (2006-) created by M. Nic,
J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8. https://doi.org/10.1351/goldbook