Atomistic mechanisms of dynamics in a two-dimensional dodecagonal quasicrystal

TL;DR

This study uses molecular dynamics simulations to explore the atomistic mechanisms of dynamics in a 2D dodecagonal quasicrystal, revealing glass-like heterogeneous relaxation behaviors and non-Arrhenius temperature dependence.

Contribution

It provides the first detailed analysis of the dynamical heterogeneity and relaxation processes in a 2D dodecagonal quasicrystal, highlighting similarities to glass-forming liquids.

Findings

Observation of two-stage relaxation dynamics in the quasicrystal.

Identification of temperature-dependent relaxation times with variable activation energy.

Dynamics resemble those of metallic glass-forming liquids more than crystalline solids.

Abstract

Quasicrystals have been observed in a variety of materials ranging from metal alloys to block copolymers. However, their structural and dynamical properties cannot be readily described in terms of conventional solid-state models of liquids and solids. We may expect the dynamics of this specific class of quasicrystalline materials to be more like glass-forming liquids in the sense of exhibiting large fluctuations in the local mobility ("dynamic heterogeneity") and non-Arrhenius temperature dependence of relaxation and diffusion. In this work, we investigate a model dodecagonal quasicrystal material in two dimensions (2D) using molecular dynamics (MD) simulations, with a focus on heterogeneous dynamics and non-Arrhenius relaxation and diffusion. As observed in glass-forming liquids and heated crystals, we observe a two-stage relaxation dynamics in the self-intermediate scattering function $F_s(k,t)$ of our quasicrystal material. It involves a fast $\beta$-relaxation and $\alpha$ relaxation process having a highly temperature dependent relaxation time whose activation energy varies in concert with the extent of string-like collective motion, a phenomenon recognized to occur in glass-forming liquids at low temperatures and crystalline materials at elevated temperatures. After examining the dynamics of our dodecagonal quasicrystalline material in great detail, we conclude that the dynamics of these materials more closely resembles observations on metallic glass-forming liquids than crystalline materials.