{"term":{"id":"12768","title":"fragile glass","longtitle":"IUPAC Gold Book - fragile glass","doi":"10.1351\/goldbook.12768","code":"12768","status":"current","definitions":[{"id":1,"text":"Glass characterised by a large value of the fragility index (m).","notes":{"1":"A very fragile glass has \\(m \\approx 250\\).","2":"A fragile glass has a markedly non-Arrhenius-type temperature dependence of the viscosity and relaxation time.","3":"The Vogel–Fulcher–Tammann equation can be used to describe the relaxation-time behaviour of a fragile glass."},"links":[{"term":"Glass","url":"https:\/\/goldbook.iupac.org\/terms\/view\/12773"},{"term":"Vogel–Fulcher–Tammann equation","url":"https:\/\/goldbook.iupac.org\/terms\/view\/12819"},{"term":"fragility index","url":"https:\/\/goldbook.iupac.org\/terms\/view\/12769"},{"term":"strong glass","url":"https:\/\/goldbook.iupac.org\/terms\/view\/12804"}],"sources":["PAC, 2013, 85, 1017. 'Glossary of terms relating to thermal and thermomechanical properties of polymers (IUPAC Recommendations 2013)' on page 1028 (https:\/\/doi.org\/10.1351\/PAC-REC-12-03-02)"]}],"altoutputs":{"html":"https:\/\/goldbook.iupac.org\/terms\/view\/12768\/html","xml":"https:\/\/goldbook.iupac.org\/terms\/view\/12768\/xml","plain":"https:\/\/goldbook.iupac.org\/terms\/view\/12768\/plain"},"citation":"Citation: 'fragile glass' 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.12768","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":"2026-08-09T08:40:10+00:00"}}