Oxide ion conduction and transporting mechanism in the layered perovskite-related material Sr2Nb2O7

Ionic conduction has been well-documented in three typical layered perovskite materials, namely Ruddlesden-Popper-type, Dion-Jacobson-type, and Aurivillius-type. In the present work, the oxide ion conduction was reported in the Sr2Nb2O7 material which also adopts a layered perovskite-related structure but does not fall into any of the above-mentioned three typical structures. The results revealed that the oxide ion conduction originated from the slight reduction of Nb5+ ions during the high-temperature synthesis process, as the sample prepared under a pure oxygen atmosphere showed more than one order of magnitude lower conductivity than the sample prepared under an ambient atmosphere. The bond-valence-based method was applied to investigate the oxide ion migration mechanism, and revealed a two-dimensional pathway within the perovskite slabs. The discovery of this new oxide ion conductor will stimulate extensive exploitation and fundamental research on other layered perovskite-related materials.