Two-Stage Melting in Core-Shell Nanoparticles: An Atomic-Scale Perspective

Microscopic understanding of thermodynamic behaviors of metallic nanoparticles is of significance for their applications in nanoscale catalysis and thermal energy storage. In this article, molecular dynamics simulations are used to investigate the thermal stabilities of Pt-Pd core-shell nanoparticles with different core sizes and shell thicknesses. Our study shows that a distinct two-stage melting occurs during the continuous heating of bimetallic nanoparticles. It has experienced a much broader temperature range compared with the melting of monometallic nanoparticles, although they have both developed from surface into interior. The temperature width for the two-stage melting is dependent not only on the bulk melting points of two component metals but also on the ratio of the shell thickness and core size. Furthermore, due to the melting of the Pd shell beforehand, the melting point of the Pt core is lower than that of the same size Pt nanoparticle not encapsulated by the Pd shell. This study provides a fundamental perspective on the melting behavior of bimetallic (even multimetallic) nanoparticles at the atomic level.