The study of the structure of molten nickel halides by neutron scattering.

The structures of molten nickel chloride, nickel bromide and nickel iodide have been investigated by applying the technique of neutron diffraction to isotopically enriched samples. The three partial structure factors and corresponding radial distribution functions which characterize the structure have been determined from the experimental data. Both steady state and pulsed neutron sources have been used for the diffraction experiments; the latter employing time-of-flight techniques. A high temperature furnace was designed for the pulsed neutron experiments and this is described. The steady state experiments used existing furnaces. The data analysis and correction procedures for both types of experiment are discussed. In conjunction with earlier studies of molten divalent chlorides, the results show that whilst the gross structural features of these 2:1 molten salts are consistent with a rigid ion model, the electronic structure of the cation appears to play an important role in determining the detailed structure. The results emphasize the importance of ionicity and charge transfer effects and the need to take these into account in model interaction potentials. A model, based on observations of the solid state, and consistent with the results presented in this thesis is discussed in which the net transfer of charge is proportional to the electronegativity of the anion. The nickel ion in molten nickel iodide appears to be considerably more mobile than in the other nickel halides. Some suggestions are made for further work to determine the mobility of the nickel ion and to test the proposed model for these systems.