Spatial Heterogeneities in Structural Temperature Cause Kovacs' Expansion Gap Paradox in Aging of Glasses

Matteo Lulli, Chun Shing Lee, Hai Yao Deng, Cho Tung Yip, Chi Hang Lam

Research output: Journal article publicationJournal articleAcademic researchpeer-review

8 Citations (Scopus)


Volume and enthalpy relaxation of glasses after a sudden temperature change has been extensively studied since Kovacs' seminal work. One observes an asymmetric approach to equilibrium upon cooling versus heating and, more counterintuitively, the expansion gap paradox, i.e., a dependence on the initial temperature of the effective relaxation time even close to equilibrium when heating. Here, we show that a distinguishable-particle lattice model can capture both the asymmetry and the paradox. We quantitatively characterize the energetic states of the particle configurations using a physical realization of the fictive temperature called the structural temperature, which, in the heating case, displays a strong spatial heterogeneity. The system relaxes by nucleation and expansion of warmer mobile domains having attained the final temperature, against cooler immobile domains maintained at the initial temperature. A small population of these cooler regions persists close to equilibrium, thus explaining the paradox.

Original languageEnglish
Article number095501
JournalPhysical Review Letters
Issue number9
Publication statusPublished - 6 Mar 2020

ASJC Scopus subject areas

  • Physics and Astronomy(all)

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