Low-Temperature Oxide-Ion Conduction Discovered in Aurivillius-Phase Sodium Bismuth Tin Oxides

Solid oxide fuel cells and other high-temperature electrochemical devices rely on fast oxide-ion conductors, yet most candidates only become truly mobile well above 500 °C. That limitation has kept system designs complex and left manufacturers with fewer material choices. A new study now challenges this constraint by engineering a family of oxide-ion conductors that perform at substantially lower temperatures, opening a path toward simpler, more durable energy systems.

Researchers report Aurivillius-type thin films described by ((Na0.5Bi0.5)n–1 TinO3n)(Bi2O2) with n = 4, 5, 7, and 8. These layered oxides combine a periodically repeating bismuth-oxide motif with a tetragonally distorted Na0.5Bi0.5TiO3 lattice, effectively creating an organized internal landscape for ion motion rather than relying on random disorder to enable conduction.

The key advance is the formation of well-defined, periodic fast ion-conducting channels. At 350 °C, the films reach an oxide-ion conductivity of 0.025 S cm−1, a value that signals ionic mobility far beyond what is typical for many solid electrolytes in this temperature regime.

To explain why the materials conduct so efficiently, the team combines atomic-scale electron ptychography with first-principles calculations. The imaging reveals localized lattice stretching, while the calculations point to how structural distortions reshape the energy pathways available to ions.

Crucially, the authors attribute the behavior to dual-ion conduction pathways triggered by specific bismuth-oxide intercalation. Instead of a single dominant route, the structure supports more than one migration channel, which collectively lowers barriers and sustains ion transport at lower thermal budgets.

The results connect design to function: by selecting the Aurivillius layering chemistry and thickness sequence (set by n), the researchers can tune the geometry of channels and distortions that guide ions through the solid. That tunability provides a blueprint for searching next-generation low-temperature electrolytes.

Finally, the work translates materials performance into device output. Fuel cells built using these films deliver a maximum power density of 0.726 W cm−2 at 400 °C, demonstrating that the conductivity gains are not merely academic but compatible with practical electrochemical operation.

Overall, the study offers a viral-science-ready message: the right layered structure can “schedule” ion motion inside a solid, enabling high oxide-ion conductivity where it was previously rare.