Real-Space Local Dynamics of Molten Inorganic Salts Using the Van Hove Correlation Function

August 2, 2022

The Science 

Transport properties in molten salt nuclear systems depend on how ions move and interact at the atomic scale, but these dynamics are difficult to measure directly. Researchers used inelastic neutron scattering combined with real-space analysis to study ion motion in molten MgCl₂. By constructing the Van Hove correlation function, they tracked how ionic positions evolve over time and distance. The results demonstrated experimentally  that molten salts exhibit correlated and structured motion rather than simple random diffusion. This link between local dynamics and liquid structure had been revealed computationally by molecular dynamics simulations, but experimental verification was lacking until this study. 

The Impact 

Understanding ion dynamics is essential for predicting viscosity, diffusion, and heat transport in molten salts. This work introduces a powerful experimental framework for directly probing atomic-scale motion in high-temperature liquids. The findings provide important benchmarks for simulations and improve understanding of how microscopic correlations influence macroscopic transport behavior. 

Summary 

This study used inelastic neutron scattering and Van Hove correlation analysis to investigate ion dynamics in molten MgCl₂. 

The measurements revealed multiple dynamic regimes. At short distances and times, ions exhibit diffusive self-motion consistent with transport processes such as ionic diffusion. At larger distances, correlated motion between ions dominates, reflecting persistent structural organization within the liquid. 

Correlations between oppositely charged ions decay rapidly, indicating frequent rearrangement of local coordination environments. In contrast, correlations between like-charged ions persist longer, suggesting the presence of intermediate-range structural organization associated with network-like ionic arrangements. 

The analysis further identified a two-step relaxation process consisting of fast local motion followed by slower structural relaxation. These collective dynamics are closely connected to macroscopic properties such as viscosity and ionic transport. 

Overall, the study demonstrates that molten salts exhibit hierarchical dynamic behavior governed by both local coordination and longer-range collective interactions, linking liquid structure directly to transport phenomena. 

Contact 

Alexander S. Ivanov, Oak Ridge National Laboratory, ivanova@ornl.gov 
Yuya Shinohara, Oak Ridge National Laboratory, shinoharay@ornl.gov 

Funding 

This work was supported by the Molten Salts in Extreme Environments Energy Frontier Research Center, funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences. This research used resources of the Spallation Neutron Source at Oak Ridge National Laboratory. 

Citation 

Shinohara, Y., A. S. Ivanov, D. Maltsev, G. E. Granroth, D. L. Abernathy, S. Dai, and T. Egami. “Real-Space Local Dynamics of Molten Inorganic Salts Using the Van Hove Correlation Function.” The Journal of Physical Chemistry Letters 13, 5956–5962 (2022). https://doi.org/10.1021/acs.jpclett.2c01230 

2022-23153  |  INT/EXT  |  Newsroom