Abstract: To improve the thermal stability of nanocrystalline (NC) metals, their interface structure can be modified by applying amorphous intergranular layers. However, traditional amorphous metallic intergranular layers are rarely formed in most pure metals or alloys. In this study, we demonstrate that amorphous oxide intergranular layers can greatly improve the thermal stability of NC metals by tailoring the grain boundaries (GBs) of NC metals. Using a Au-ZrO₂ model system, ultra-fine Au nanoparticles (∼ 3 nm) with exceptional thermal stability at temperatures up to 600 °C were formed after introducing amorphous ZrO₂ intergranular layers at the GBs of NC Au. Quantitative thermodynamic model calculations revealed that the exceptional thermal stability of the Au nanoparticles originated fundamentally from the formation of low-energy Au|ZrO₂ interfaces. The kinetic stabilization was further discussed, showing that the Ostwald ripening of Au nanoparticles was suppressed due to the presence of amorphous ZrO₂ intergranular. This study sheds light on new strategies for enhancing the thermal stability of NC metals by utilizing amorphous oxide intergranular layers, paving the way for the achievement of ultra-stable NC metals through interface modification.

Key words: Nanocrystalline metals, Thermal stability, Amorphous intergranular layers, Grain growth, Interface thermodynamics