In this paper we consider grain boundary sliding as a dominant mechanism of plasticity in nanocrystalline metals. A mechanical model for barrier resistance to sliding has been proposed. Characteristic time of plastic relaxation due to grain boundary sliding has been estimated based on molecular dynamics simulation data. At quasi-static deformation yield strength is determined by barrier resistance, and the predicted threshold stresses are in good agreement with experimental data.

Improving the mechanical performance of nanocrystalline functional oxides can have major implications for stability and resilience of battery cathodes, development of reliable nuclear oxide fuels, strong and durable catalytic supports. By combining Monte Carlo simulations, experimental thermodynamics, and in-situ transmission electron microscopy, we demonstrate a novel toughening mechanism based on interplay between the thermo-chemistry of the grain boundaries and crack propagation. By using zirconia as a model material, lan-thanum segregation to the grain boundaries was used to increase the toughness of individual boundaries and simultaneously promote a smoother energy landscape in which cracks experience multiple deflections through the grain boundary network, ultimately improving fracture toughness.