Diffusion Kinetics in Binary Liquid Alloys with Ordering and Demixing Tendencies

Abstract

Theoretical relationship between collective and tracer diffusion coefficients has been derived and tested for different types of binary melts: (i) with an ordering tendency (case study on Ni–Al and Ni–Zr melts) and (ii) with a demixing tendency (case study on Cu–Ag melts). The obtained relationship explicitly demonstrates microscopic cross-correlation effects in the kinetics of collective diffusion. Our approach incorporates molecular dynamics calculations, modelling and statistical mechanical analysis based on fundamental concepts of the fluctuation-dissipation theorem, generalized Langevin equation and Mori-Zwanzig formalism. We also applied the developed theory to interpret recent available experimental data as well as our molecular dynamics data of diffusion kinetics in different types of binary melts: with chemical ordering and contrarily with demixing tendency.