06592 IUPAC Gold Book - valence transition 10.1351/goldbook.V06592 V06592 current 1 A transition observed in certain rare-earth and actinide materials in which the electronic occupation of the 4f or 5f orbital changes with external conditions for example, temperature and pressure. Example: The transition at approximately \(0.65\ \rm{GPa}\) where black, semiconducting $\ce{Sm^{2+}S^{2−}}$ changes to golden metallic $\ce{(Sm^{3+} + e^{−})S^{2-}}$. PAC, 1994, 66, 577. 'Definitions of terms relating to phase transitions of the solid state (IUPAC Recommendations 1994)' on page 593 (https://doi.org/10.1351/pac199466030577) https://goldbook.iupac.org/terms/view/V06592/html https://goldbook.iupac.org/terms/view/V06592/json https://goldbook.iupac.org/terms/view/V06592/plain Citation: 'valence 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.V06592 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. If you are interested in licensing the Gold Book for commercial use, please contact the IUPAC Executive Director at executivedirector@iupac.org . 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. 2026-05-10T17:20:10+00:00