Solid oxide fuel cells (SOFCs) are devices for converting liquid or gaseous fuels directly to electrical current. They rely on high oxide ion conductivity throughout the device for efficient operation but their performance is limited by the poor ionic conductivity of current commercial cathode materials. These problems can only be avoided by employing high operating temperatures (typically around 800 °C), resulting in high running costs and degradation of the device. The identification and synthesis of new mixed electronic-ionic conducting (MIEC) oxides with superior ionic transport properties is therefore of critical importance to the development of this technology. We intend to use neutron diffraction to investigate the structures of a new family of potential SOFC materials, which may ultimately lead to structural control of their properties.