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, and Chi-Hang Lam
Phys. Rev. Lett. 124, 095501 – Published 6 March 2020
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Abstract

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.

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  • Received 6 September 2019
  • Accepted 5 February 2020

DOI:https://doi.org/10.1103/PhysRevLett.124.095501

© 2020 American Physical Society

Physics Subject Headings (PhySH)

  1. Research Areas
  1. Physical Systems
Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Matteo Lulli1,2, Chun-Shing Lee1, Hai-Yao Deng3,4, Cho-Tung Yip5, and Chi-Hang Lam1,*

  • 1Department of Applied Physics, Hong Kong Polytechnic University, Hong Kong, China
  • 2Department of Mechanics and Aerospace Engineering, Southern University of Science and Technology, Shenzhen, Guangdong 518055, China
  • 3School of Physics and Astronomy, The University of Manchester, Manchester M13 9PL, United Kingdom
  • 4School of Physics and Astronomy, Cardiff University, The Parade, Cardiff CF24 3AA, United Kingdom
  • 5School of Science, Harbin Institute of Technology, Shenzhen Graduate School, Shenzhen, Guangdong 518055, China

  • *C.H.Lam@polyu.edu.hk

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Issue

Vol. 124, Iss. 9 — 6 March 2020

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