On the oxide ion conductivity of potassium doped strontium silicates

Recent reports of remarkably high oxygen ion conductivity in a new family of layered strontium silicates have questioned the rationale for materials design in solid electrolytes. Here, we present a re-investigation of the crystal structure, microstructure, total conductivity and perform the first direct investigation of oxygen ion diffusivity of a nominal Sr0.8K0.2Si0.5Ge0.5O2.9 composition. The results show very low levels of oxide ion conductivity, which do not correlate with total electrical conductivity. Furthermore, sub-micron elemental mapping reveals a previously unreported inhomogeneous chemical composition. The absence of evidence for secondary phases in the diffraction data suggests that the additional phases are amorphous in nature.