Assessing relationships between self-diffusion coefficient and viscosity in Ni-Al alloys based on the pair distribution function
QL Cao and F Tu and L Xue and FH Wang, JOURNAL OF APPLIED PHYSICS, 126, 105108 (2019).
Based on the pair distribution function g(r), molecular dynamics simulations on NiAl and Ni3Al melts were carried out to investigate the relationships between self-diffusion coefficient and viscosity. The self-diffusion coefficients of Ni in melts and the viscosity of melts were calculated using the Einstein relation and Green-Kubo equation, respectively. Our result shows that there is a crossover in the self- diffusion coefficient and viscosity from high-temperature Arrhenius behavior to low-temperature non-Arrhenius behavior, and the crossover is accompanied by the breakdown of Stokes-Einstein relation (SER) and the onset of fractional Stokes-Einstein relation. The breakdown temperature of SER is nearly twice the glass-transition temperature and much higher than the mode-coupling critical temperature for both NiAl and Ni3Al melts. Further analyses based on g(r) suggest that temperature dependences of the pair correlation entropy and the partial pair correlation entropy of components may be used as probes for testing the validity of Stokes-Einstein relation and predicting its breakdown temperature.
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