Enhanced Thermal Stability of Ni@TiO2 Core-Shell Nanoparticles

Ni@TiO2 core–shell nanoparticles were synthesized by magnetron sputtering and their structure verified by HRTEM and EDS analysis. The thermal stability of these particles was investigated using in situ TEM annealing and compared with that of pure Ni nanoparticles. While pure Ni particles sinter at 450 °C and exhibit significant growth at 800 °C, Ni@TiO2 nanoparticles remain stable up to 700 °C, with the sintering onset between 700 and 800 °C. A simple thermal-mismatch model was applied to explain the stabilizing effect of the TiO2 shell, demonstrating that differences in thermal expansion between Ni and TiO2 generate interface stresses sufficient to crack the shell after the amorphous–rutile transformation. The TiO2 coating effectively delays Ni coalescence by 250 °C relative to bare Ni, highlighting its role as a protective shell against high-temperature sintering.