Enhancement of the chemical stability in confined δ-Bi2O3

Using highly coherent interfaces of alternating oxide layers a bismuth-oxide-based oxygen ion conductor exhibits unprecedented high chemical stability in reducing conditions and during redox cycles at high temperature. Bismuth-oxide-based materials are the building blocks for modern ferroelectrics 1 , multiferroics 2 , gas sensors 3 , light photocatalysts 4 and fuel cells 5 , 6 . Although the cubic fluorite δ-phase of bismuth oxide (δ-Bi 2 O 3 ) exhibits the highest conductivity of known solid-state oxygen ion conductors 5 , its instability prevents use at low temperature 7 , 8 , 9 , 10 . Here we demonstrate the possibility of stabilizing δ-Bi 2 O 3 using highly coherent interfaces of alternating layers of Er 2 O 3 -stabilized δ-Bi 2 O 3 and Gd 2 O 3 -doped CeO 2 . Remarkably, an exceptionally high chemical stability in reducing conditions and redox cycles at high temperature, usually unattainable for Bi 2 O 3 -based materials, is achieved. Even more interestingly, at low oxygen partial pressure the layered material shows anomalous high conductivity, equal or superior to pure δ-Bi 2 O 3 in air. This suggests a strategy to design and stabilize new materials that are comprised of intrinsically unstable but high-performing component materials.