The role of the thermodynamic factor on the intrinsic and tracer diffusivities in binary mixtures

TL;DR

This paper investigates how the thermodynamic factor influences intrinsic and tracer diffusivities in binary mixtures, revealing that intrinsic diffusivity is independent of the thermodynamic factor, supported by theoretical analysis and experimental data.

Contribution

It demonstrates that the intrinsic diffusivity does not depend on the thermodynamic factor, simplifying previous theoretical models and confirming findings with experimental data.

Findings

Intrinsic diffusivity is independent of the thermodynamic factor.

Theoretical analysis confirms the independence of intrinsic diffusivity from $\

,

Abstract

One of the Darken equations gives a relationship between the intrinsic and the tracer diffusion coefficients, $D_A$ and $D_A^*$, of species $A$ in a solid binary mixture. In its original version, the equation reads $D_A = D_A^* \Gamma$, with $\Gamma$ the thermodynamic factor. The question addressed in this paper is how $D_A$ and $D_A^*$ depend separately on $\Gamma$. Using a recent result for transition probabilities in terms of the excess chemical potential (M. Di Muro and M. Hoyuelos, Phys. Rev. E 104, 044104, 2021), it is shown that the intrinsic diffusivity does not depend on $\Gamma$. This approach simplifies a previous theoretical analysis that reaches the same result. Experimental results of diffusion in a Ni-Pd and Fe-Pd alloys (M. J. H. van Dal et al., Acta mater. 48, 385, 2000) are used to check the theory.