Stabilizing nanocrystalline grains in ceramic-oxides. 
Nanocrystalline ceramic-oxides are prone to grain growth rendering their highly attractive properties practically unusable.  Using atomistic simulations of ceria as a model material system, we elucidate a framework to design dopant-pinned grain boundaries that prevent this grain growth.  While in metallic systems it has been shown that a large mismatch between host and dopant atomic sizes prevents grain growth, in ceramic-oxides we find that this concept is not applicable.  Instead, we find that dopant-oxygen vacancy interaction, i.e., dopant migration energy in the presence of an oxygen vacancy, and dopant-oxygen vacancy binding energy are the controlling factors in grain growth.  Our prediction agrees with and explains previous experimental observations.