Synthesis, structure and conductivity of sulfate and phosphate doped SrCoO3

In this paper we report the successful incorporation of sulfate and phosphate into SrCoO3 leading to a change from a 2H– to a 3C–perovskite polymorph. Structural characterization by neutron diffraction showed extra weak peaks related to oxygen vacancy ordering, and these could be indexed on an expanded tetragonal cell, containing two inequivalent Co sites, similar to previously reported for Sb doped SrCoO3. Conductivity measurements on the doped systems showed a large enhancement compared to the undoped hexagonal system, consistent with corner–sharing of CoO6 octahedra for the former. Further work on the doped samples shows, however, that they are metastable, transforming back to the hexagonal cell on annealing at intermediate temperatures. The incorporation of Fe was shown, however, to improve the stability at intermediate temperatures, and these co–doped phases also showed high conductivities.