Neutron scattering studies of molten salts

A number of neutron scattering experiments have been performed in order to obtain structural and dynamical information about some molten salts. Inelastic scattering has produced information about the dispersion of the optic mode in molten caesium chloride in the equivalent of the first Brillouin zone. A diffraction experiment, using isotopic substitution, on lithium chloride leads to the conclusion that the cation-anion coordination is approximately tetrahedral, a result that meets the predictions of simulations; it also demonstrates the difficulties produced by small systematic errors in experiments of this type. Due to equipment failure an experiment on a mixture of lithium chloride and potassium chloride was inconclusive but it is clear that it is feasible and should be repeated. Diffraction and inelastic neutron scattering experiments on silver iodide in its molten and fast ion conducting alpha phase show that the disordered structure of the two is very similar and not unlike that of molten cuprous chloride in having very little structure in the cation-cation correlation. In contrast the dynamics differ considerably - in addition to an acoustic mode the melt shows strong modes that have dispersion curves approximately at constant Q; these modes, which are related to the peaks in the static structure factor, are not seen in the alpha phase. The temperature dependence of molten caesium chloride has been investigated using the time of flight diffractometer LAD. The analysis of this data required new correction procedures including consideration of inelasticity corrections and resolution effects. These are discussed and the latter is treated using a maximum entropy method. The structure is found to vary little over the temperature range used, less than is predicted by simulation. The results are not consistent with the hypothesis that the discrepancy between simulation and experiment for this salt is due to incorrect scaling of the simulation potential.