Sodium cobalate has emerged as one of the best thermoelectric materials. Our previous neutron Laue diffraction studies on SXD have found ordered arrays of multivacancy clusters, and these are responsible for the thermoelectric performance. Many of the applications are at high temperatures, including power recovery from car exhausts. Thus, we now propose to study the superstructures in the SXD furnace over the range 300 - 900K. For strontium doped samples we expect to find that the range of stability of the superstructure is much greater than for the pure compound. In the case of calcium doped samples the multivacancy clusters are different to the strontium-doped and pure compounds, and different reordering transitions are expected at elevated temperatures. Finally, we expect to see rings of diffuse scattering from short range ordering of clusters well into the disordered phase.