Term: λ-transition (lambda-transition) https://doi.org/10.1351/goldbook.T03420 Definition: A second-order or higher-order transition, in which the heat capacity shows either a discontinuity (second-order) or a vertex (higher-order) at the transition temperature. Example: The transition at 846 K, accompanied by a finite change in specific heat capacity at constant pressure Cp, of the low-temperature polymorph of quartz to the high-temperature polymorph. Related Terms: 1) second-order (http://doi.org/10.1351/goldbook.S05531). 2) higher-order transition (http://doi.org/10.1351/goldbook.H02822). 3) heat capacity (http://doi.org/10.1351/goldbook.H02753). 4) specific heat capacity (http://doi.org/10.1351/goldbook.S05800). Source: PAC, 1994, 66, 577. 'Definitions of terms relating to phase transitions of the solid state (IUPAC Recommendations 1994)' on page 584 (https://doi.org/10.1351/pac199466030577) Citation: 'λ-transition (lambda-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.T03420 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. 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.