Ionic structure and transport properties of KF-NaF-AlF3 fused salt: a molecular dynamics study

XJ Lv and ZX Han and HX Zhang and QS Liu and JA Chen and LX Jiang, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 21, 7474-7482 (2019).

DOI: 10.1039/c9cp00377k

We used the first-principles molecular dynamics simulations combined with the interatomic potential molecular dynamics to study the ionic structure and transport properties of KF-NaF-AlF3 fused salt. Simulation results show that the ionic structure of KF-NaF-AlF3 fused salt is principally dominated by the distorted five-coordinated AlF5(2-) and six-coordinated AlF6(3-) groups. When melting to a liquid, a part of the six-coordinated AlF6(3-) group dissociated into the four- coordinated AlF4(-) and five-coordinated AlF5(2-) groups. Four, five and six-coordinated aluminum-fluoro complexes coexist in KF-NaF-AlF3 fused salt, while the tetrahedral AlF4(-) groups are relatively rare. The content of the bridging fluorine atom is relatively small, about 5-11%, which indicates that the polymerization degree of the ionic structure of the KF-NaF-AlF3 fused salt system is lower. The KF-NaF-AlF3 fused salt has better liquidity and ionic conductivity due to the high self-diffusion coefficients of all particles in the fused salt system. KF can effectively break the F atom bridges, which reduces the polymerization degree of the ionic structure of the fused salt system and increases its ionic conductivity.

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