Enhancement of the chemical stability in confined δ-Bi2O3

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 delta-phase of bismuth oxide (delta-Bi2O3) exhibits the highest conductivity of known solid-state oxygen ion conductors(5), its instability prevents use at low temperature(7-10). Here we demonstrate the possibility of stabilizing delta-Bi2O3 using highly coherent interfaces of alternating layers of Er2O3-stabilized delta-Bi2O3 and Gd2O3-doped CeO2. Remarkably, an exceptionally high chemical stability in reducing conditions and redox cycles at high temperature, usually unattainable for Bi2O3-based materials, is achieved. Even more interestingly, at low oxygen partial pressure the layered material shows anomalous high conductivity, equal or superior to pure delta-Bi2O3 in air. This suggests a strategy to design and stabilize new materials that are comprised of intrinsically unstable but high-performing component materials.