order–disorder transition

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. Examples:
  1. The transition of LiFeO2, with a tetragonal @U06562@, in which the Li+ and Fe3+ cations are perfectly ordered on crystallographically non-equivalent octahedral sites to cubic LiFeO2 in which the Li+ and Fe3+ cations are distributed randomly over all the octahedral sites.
  2. The transition of orthorhombic KCN to cubic KCN in which the CN ions become oriented in any of the eight [111] directions.
  3. A @S06137@
PAC, 1994, 66, 577. (Definitions of terms relating to phase transitions of the solid state (IUPAC Recommendations 1994)) on page 587 [Terms] [Paper]