  New highly oxygen-active materials may enhance many energy-related
technologies by enabling efficient oxygen-ion transport at lower temperatures,
e.g., below 400 Celsius. Interstitial oxygen conductors have the potential to
realize such performance but have received far less attention than
vacancy-mediated conductors. Here, we combine physically-motivated structure
and property descriptors, ab initio simulations, and experiments to demonstrate
an approach to discover new fast interstitial oxygen conductors. Multiple new
families were found which adopt completely different structures from known
oxygen conductors. From these families, we synthesized and studied oxygen
kinetics in La4Mn5Si4O22+d (LMS), a representative member of
perrierite/chevkinite family. We found LMS has higher oxygen ionic conductivity
than the widely used yttria-stabilized ZrO2, and among the highest surface
oxygen exchange rates at intermediate temperature of known materials. The fast
oxygen kinetics is the result of simultaneously active interstitial and
interstitialcy diffusion pathways. This work developed and demonstrated a
powerful approach for discovering new families of interstitial oxygen
conductors and suggests many more such materials remain to be discovered.
