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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 unit cell, 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 superconducting transition
PAC, 1994, 66, 577 (Definitions of terms relating to phase transitions of the solid state (IUPAC Recommendations 1994)) on page 587
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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: (2006-) created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8.
Last update: 2014-02-24; version: 2.3.3.
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