Coarsening of nanocrystalline systems at elevated temperatures can be prevented by adding small amounts of impurities to grain boundaries and interfaces, as found in a variety of instances. For the model systems CuBi and CuAg we investigate atomic-scale mechanisms, which underlie stabilization of the nanophase in the presence of an open surface, using experiments, molecular dynamics computer simulations, and thermodynamic considerations. We find that the occurrence of locally negative grain boundary free energies due to dopants is sufficient to frustrate grain growth via a metastable equilibrium. Our treatment can be generalized to other systems with grain boundary segregation.

• Received 22 October 2006

DOI:https://doi.org/10.1103/PhysRevB.76.024111