Term: higher-order transition
https://doi.org/10.1351/goldbook.H02822

Definition:
A general term used to describe a transition in which the first and second derivatives of the molar Gibbs energy or molar Helmholtz energy (or chemical potential) with respect to temperature and pressure are continuous, but derivatives of some higher order are discontinuous at the transition point. Synonymous with smooth transition.

Related Terms:
1) gibbs energy (http://doi.org/10.1351/goldbook.G02629).
2) helmholtz energy (http://doi.org/10.1351/goldbook.H02772).
3) chemical potential (http://doi.org/10.1351/goldbook.C01032).

Source: PAC, 1994, 66, 577. 'Definitions of terms relating to phase transitions of the solid state (IUPAC Recommendations 1994)' on page 583 (https://doi.org/10.1351/pac199466030577)

Citation: 'higher-order transition' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.H02822

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