We wish to collect powder neutron diffraction data on modified bornites, Cu5Fe1-xNixS4 (0<x<0.1) to study the impact of nickel substitution on the distribution of cations over tetrahedral sites in the antifluorite and zinc blende sub-cells. In particular, we wish to establish if the preferential occupation by Fe3+ of sites in the antifluorite sub-cell we have identified in bornite, is retained on nickel substitution. We will explore the evolution of structure with composition by collecting data at room temperature for a range of nickel contents. We will also investigate structural changes through two vacancy-disordering transitions, by collection of data as a function of temperature Detailed structural data are essential to efforts to understand the changes in thermoelectric properties that result from nickel substitution, which significantly enhance the figure of merit;