Structure and dynamics in yttrium-based molten rare earth alkali fluorides

Area of Science:

• Materials Science
• Physical Chemistry
• Computational Chemistry

Background:

• Molten salts are crucial for various applications, including batteries and nuclear reactors.
• Understanding their transport properties, like diffusion and conductivity, is essential for optimizing performance.
• Previous studies often linked anion diffusion to metal-cation coordination, but this link needs further investigation.

Purpose of the Study:

• To investigate the transport properties of molten LiF-YF3 mixtures.
• To explore the relationship between microscopic structure and dynamic properties.
• To evaluate the predictive power of coordination numbers versus ionic bond lifetime on diffusion coefficients.

Main Methods:

• Pulsed field gradient nuclear magnetic resonance (PFGM-NMR) spectroscopy.
• Potentiometric experiments.
• Molecular dynamics (MD) simulations.

Main Results:

• Calculated diffusion coefficients and electric conductivities showed excellent agreement with experimental measurements across various compositions.
• Analysis of MD simulations revealed static and dynamic quantities, including radial distribution functions and cage correlation functions.
• Coordination number was found to be a poor predictor of anion diffusion coefficient evolution; ionic bond lifetime emerged as a more relevant metric.

Conclusions:

• The study challenges the conventional view that anion diffusion is primarily governed by coordination with metal cations.
• Ionic bond lifetime provides a more accurate indicator for predicting diffusion coefficients in molten salts like LiF-YF3.
• Findings have implications for the Nernst-Einstein relation's validity in estimating electrical conductivity in these systems.