An isotopic substitution study of and binary molten salt mixtures

The scattering from binary molten salt mixtures of nominally two thirds alkali halide concentration, where x = `natural', `zero-scattering' and `62' enrichments of nickel, has been measured by time-of-flight neutron diffraction on ISIS LAD. A complementary experiment was performed on molten samples, also of nominally two thirds alkali halide concentration, using isotopic substitution of chlorine. In the case of - KCl, the results indicate a large first sharp diffraction peak (FSDP) in and but not in . Reverse Monte Carlo (RMC) modelling indicates a well-ordered, almost regularly tetrahedral local structure for the ion, the preponderance of large ions as next-nearest neighbours to the metal cation and the apparent association of this with enhanced intermediate-range order (IRO) in the mixtures. The results confirm the findings of the initial composition study of this system and provide further support for the suggestion that enhanced IRO arises from ordering between tetrahedral units and alkali counter-ions. Modelling of the data suggests a strong similarity with molten even though the pure and molten salt structures are confirmed to be dissimilar.