Shape-Dependence on the Deformation Mechanism of Small Platinum Nanoparticles at High Temperature

In addition to traditional displacive plasticity mechanisms where the atoms move in a collective fashion, deformation in small nanoparticles can also occur via surface diffusion. At the macroscale, diffusion often occurs at high temperatures and can be correlated to the melting point. For nanoparticles, the contribution of diffusive plasticity also depends strongly on particle size, resulting in nanoscale creep. As the nanoparticle size reduces, there are more atoms at the surface compared to the bulk which have fewer neighboring atoms, thus reducing the diffusion activation energy and reducing the melting point. While the effects of temperature, size, and strain rate on nanoparticle deformation have been previously investigated, the role of particle shape remains largely undefined.<br/>We used molecular dynamics models to study the effects of surface energy and shape on the deformation mechanism of platinum nanoparticles under compression at temperatures ranging between 300 K and 800 K for three different shapes and three different sizes. A transition from displacive to diffusive deformation mechanism was observed for all nanoparticles with the increase in temperature. The results also demonstrate significant differences in deformation mechanisms between differently shaped particles, even for the same diameter, temperature, and strain rate. These differences are linked to the surface energy and diffusivity of the different facets and edges. Our findings provide a new understanding of the previously unexplored role of surface energy in the deformation of small metal nanoparticles, enabling the calculation of size-, shape-, and temperature-dependent nanoparticle properties and deformation mechanisms. Such understanding is crucial for designing nanoparticle-based systems where changes in properties occur from nanoparticle structural changes due to plastic deformation.