We request 5 days beamtime on the Polaris diffractometer to perform simultaneous ionic conductivity and neutron powder diffraction measurements of five superionic binary halides. A systematic study of compounds which possess a second order transition to the highly conducting superionic state on heating (SrCl2 and BaF2) and those which have been reported to undergo first-order transitions at elevated temperatures (PbCl2, BaCl2 and SrBr2) will provide a direct insight into the structure-property relationships. This study will provide a detailed investigation of the thermal evolution of the lattice parameter, defect structure, defect concentration and defect activation energy and assess the influence of ionic size on the ionic conduction properties within these 'simple' model superionic compounds.