Thermal stability of Cu@Ag core–shell nanoparticles

• Thermal stability of Cu@Ag core–shell NPs upon heating was evaluated.
• Oxidation of nanoparticles was monitored by synchrotron radiation X-ray diffraction.
• Phase transitions and morphological evolution were investigated.
• Mechanisms for the coalescence of Cu cores and ripening of Ag shell were explained.

In this study, the structural evolution and oxidation of Cu@Ag core–shell nanoparticle deposits (with average particle diameter of 25 nm and Ag/Cu atomic ratio of 1/8) upon heating in air were investigated quantitatively via in situ synchrotron radiation X-ray diffraction. With an increasing temperature, the coalescence of Cu cores and ripening of Ag shell occurred simultaneously, resulting in discrete Ag nanonodules and unprotected Cu microparticles. Due to the protection of the thin Ag shell, the formation temperatures of the Cu oxides for Cu@Ag NPs were higher than those for pure Cu nanoparticles with similar size by at least 150 °C.