Na0.5Bi0.5TiO3 (NBT) based materials can present high level of oxide-ion conduction and therefore they are promising electrolytes for IT-SOFCs. The conductivity of highly conductive compositions of NBT materials present a change in activation energy around 325C, which falls in the temperature range where two polymorphs (R3c and P4bm) coexist. Here we request to collect neutron diffraction (ND) data on two compositions of a NBT based solid solution. The key objectives are 1) to determine the variation in the relative amounts of two polymorphs across the solid solution; and 2) to establish the possible relationship between conductivity and polymorphs of NBT materials and to further understand the oxide-ion conduction mechanism in NBT-based materials.