We have recently been studying a series of rhenium-cobalt oxide phases, based on the cation deficient perovskite phase Ba4Re2CoO12. Lithium can be inserted into the vacant sites in this phase, either by low-temperature topochemical routes, or via high temperature ceramic synthesis. We propose to collect neutron powder diffraction data from the Ba4Re2CoLiO12 phases to establish their accurate crystal structures, and establish if any Co/Li order is present. In addition we will also collect low-temperature datasets to investigate the magnetic order in these doped phases.The topochemical synthesis route deintercalates oxygen during the lithium insertion process, and results in a ferromagnetic material. We propose to collect neutron powder diffraction data from this Ba4Re2CoLiO12-x phase to establish the location of the oxygen vacancies and the nature of the magnetic state adopted.