{"term":{"id":"01189","title":"commensurate–incommensurate transition","longtitle":"IUPAC Gold Book - commensurate–incommensurate transition","doi":"10.1351\/goldbook.C01189","code":"C01189","status":"current","mentioned":"<em>mentioned<\/em>: lock-in state","definitions":[{"id":1,"text":"A transition between two states having magnetic or crystallographic structures with a basic lattice and an imposed super-periodicity. In the commensurate (lock-in) state this super-periodicity is a simple rational multiple of the basic unit cell. In the incommensurate state the ratio of the super-periodicity repeat distance to the basic lattice repeat distance is irrational and may show continuous variation with variation in some degree of freedom (e.g. temperature, pressure, composition) of the system. ","notes":{"1":"A commensurate–incommensurate transition also occurs in liquid-crystal systems where there is an incommensurability in the packing of dimers in relation to monomers."},"exams":{"1":"The transition of $\\ce{Rb2ZnCl4}$ from an incommensurate structure to a commensurate structure at the lock-in temperature, \\(T_{\\rm{L}}\\), which is dependent on the crystal growth method and varies in the range \\(128\\ \\rm{K}\\) to \\(190\\ \\rm{K}\\)."},"links":[{"term":"unit cell","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/U06562"}],"sources":["PAC, 1994, 66, 577. 'Definitions of terms relating to phase transitions of the solid state (IUPAC Recommendations 1994)' on page 579 (https:\/\/doi.org\/10.1351\/pac199466030577)"]}],"altoutputs":{"html":"https:\/\/goldbook.iupac.org\/terms\/view\/C01189\/html","xml":"https:\/\/goldbook.iupac.org\/terms\/view\/C01189\/xml","plain":"https:\/\/goldbook.iupac.org\/terms\/view\/C01189\/plain"},"citation":"Citation: 'commensurate–incommensurate transition' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351\/goldbook.C01189","license":"The IUPAC Gold Book is licensed under Creative Commons Attribution-ShareAlike CC BY-SA 4.0 International (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0\/) for individual terms.","collection":"If you are interested in licensing the Gold Book for commercial use, please contact the IUPAC Executive Director at executivedirector@iupac.org .","disclaimer":"The International Union of Pure and Applied Chemistry (IUPAC) is continuously reviewing and, where needed, updating terms in the Compendium of Chemical Terminology (the IUPAC Gold Book). Users of these terms are encouraged to include the version of a term with its use and to check regularly for updates to term definitions that you are using.","accessed":"2026-07-21T16:02:31+00:00"}}