Structural effects on the electrical conductivity of molten fluorides: Comparison between LiF–YF3 and LiF–NaF–ZrF4

The electrical conductivities of molten LiF–YF3 and LiF–NaF–ZrF4 have been obtained from impedance measurements and molecular dynamics simulations, and discussed through the analysis of the local structure of the liquid. The conductivity decreases with addition of MFn (Mn+ = Y3+ or Zr4+) in the melt due to the formation of M F x n − x units, which can be either isolated or linked via bridging fluorine. Structural differences have been put in evidence depending on the nature of the multivalent metallic species (Y3+ and Zr4+) added in the alkali fluoride solvent regarding the stability of the M F x n − x units and the length m of [ M F x n − x ] m chains. These differences are at the origin of a more pronounced decrease of the electrical conductivity in the Zr-containing fused salts in the low MFn concentration régime.