  The transport properties of molten LiF-YF3 mixtures have been studied by
pulsed field gradient nuclear magnetic resonance spectroscopy, potentiometric
experiments, and molecular dynamics simulations. The calculated diffusion
coefficients and electric conductivities compare very well with the
measurements accross a wide composition range. We then extract static (radial
distribution functions, coordination numbers distributions) and dynamic (cage
correlation functions) quantities from the simulations. Then, we discuss the
interplay between the microscopic structure of the molten salts and their
dynamic properties. It is often considered that variations in the diffusion
coefficient of the anions are mainly driven by the evolution of its
coordination with the metallic ion (Y3+ here). We compare this system with
fluorozirconate melts and demonstrate that the coordination number is a poor
indicator of the evolution of the diffusion coefficient. Instead, we propose to
use the ionic bonds lifetime. We show that the weak Y-F ionic bonds in LiF-YF3
do not induce the expected tendency of the fluoride diffusion coefficient to
converge toward the one of yttrium cation when the content in YF3 increases.
Implications on the validity of the Nernst-Einstein relation for estimating the
electrical conductivity are discussed.
