Abstract
We propose an atomistic model for correlated particle dynamics in liquids and glasses predicting both slow stretched-exponential relaxation (SER) and fast compressed-exponential relaxation (CER). The model is based on the key concept of elastically interacting local relaxation events. SER is related to slowing down of dynamics of local relaxation events as a result of this interaction, whereas CER is related to the avalanche-like dynamics in the low-temperature glass state. The model predicts temperature dependence of SER and CER seen experimentally and recovers the simple, Debye, exponential decay at high temperature. Finally, we reproduce SER to CER crossover across the glass transition recently observed in metallic glasses.
Highlights
As a matter of general principle in physics, correlations tend to decay in time and space
We propose an atomistic model for correlated particle dynamics in liquids and glasses predicting both slow stretched-exponential relaxation (SER) and fast compressed-exponential relaxation (CER)
We show that CER follows from a kinetic equation governing the dynamics of elastically interacting local relaxation event (LRE)
Summary
As a matter of general principle in physics, correlations tend to decay in time and space. The two processes can be combined into a unifying description that provides the experimentally observed crossover from SER above Tg to CER below Tg. Earlier work considered LREs in glasses and related elastic effects [25,26,27,28,29]. Let us consider the current number of LREs n(t), induced in a system by an external perturbation such as fixed shear or compressive stress or by a long-range internal stress field This number n(t) comes in addition to thermally-induced LREs. When n(t) tends to its limiting value nr at long times, the perturbation is relaxed to zero. This picture is consistent with glassy relaxation in supercooled liquids, where the system trickles down towards lower states in the energy landscape, characterized by higher barriers [10]
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