Abnormal breakdown of Stokes-Einstein relation in liquid aluminium

CH Li and XJ Han and YW Luan and JG Li, CHINESE PHYSICS B, 26, 016102 (2017).

DOI: 10.1088/1674-1056/26/1/016102

We present the results of systematic molecular dynamics simulations of pure aluminium melt with a well-accepted embedded atom potential. The structure and dynamics were calculated over a wide temperature range, and the calculated results (including the pair correlation function, self-diffusion coefficient, and viscosity) agree well with the available experimental observations. The calculated data were used to examine the Stokes-Einstein relation (SER). The results indicate that the SER begins to break down at a temperature T-x (similar to 1090 K) which is well above the equilibrium melting point (912.5 K). This high-temperature breakdown is confirmed by the evolution of dynamics heterogeneity, which is characterised by the non-Gaussian parameter alpha(2) (t). The maximum value of alpha(2) (t), alpha(2, max), increases at an accelerating rate as the temperature falls below T-x. The development of alpha(2, max) was found to be related to the liquid structure change evidenced by local fivefold symmetry. Accordingly, we suggest that this high-temperature breakdown of SER has a structural origin. The results of this study are expected to make researchers reconsider the applicability of SER and promote greater understanding of the relationship between dynamics and structure.

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