Synthesis of silicon doped SrMO3 (M = Mn, Co): stabilization of the cubic perovskite and enhancement in conductivity

In this paper we report the successful incorporation of silicon into SrMO3 (M = Co, Mn) leading to a structural change from a hexagonal to a cubic perovskite. For M = Co, the cubic phase was observed for low doping levels (3%), and these doped phases showed very high conductivities (up to approximate to 350 Scm(-1) at room temperature). However, annealing studies at intermediate temperatures (700-800 degrees C), indicated that the cubic phase was metastable with a gradual transformation to a hexagonal cell on annealing. Further work showed that co-doping with Fe resulted in improved stability of the cubic phase; a composition SrCo0.85Fe0.1Si0.05O3-y displayed good stability at intermediate temperatures and a high ;conductivity (approximate to 150 Scm(-1) at room temperature). For M = Mn, the work showed that higher substitution levels were required to form the cubic perovskite (approximate to 15% Si doping), although in these cases the phases were shown to be stable to annealing at intermediate temperatures. Conductivity measurements again showed an enhancement in the conductivity on Si doping, although the conductivities were lower (approximate to 0.3-14 Scm(-1) in the range 20-800 degrees C) than the cobalt containing systems. The conductivities of both systems suggest potential for use as cathode materials in solid oxide fuel cells.