Comprehensive understanding of thermodynamic properties of metallic nanoparticles is of significance for their utility in catalysis. In this article, we have employed molecular dynamics simulations with quantum Sutton−Chen many-body potentials to examine the thermal stability of Au−Pt core−shell nanoparticles with different sizes during continuous heating. Our study shows that, for fixed particle size, the melting temperature is independent of core size for a small core while it is linearly decreased with a rising core radius for a large core. Diverse melting mechanisms have been discovered for different-core-sized nanoparticles. For a small core, the melting is progressively developed from the surface into the core, similar to that of monometallic nanoparticles. For a moderate or large core, an inhomogeneous melting has been found in these nanoparticles. The nucleation and activity of Shockley partial dislocations have initialized the local structural instability of the core−shell interface, leading to the inhomogeneous premelting of the Au core and the Pt shell for the moderate core. Nevertheless, when the core is large enough (resulting superthin shell), the diffusion of Au atoms from the core into the shell plays a dominant role in the destruction of the core−shell interface. This study provides a fundamental perspective on the melting behaviors of bimetallic (even multimetallic) nanoparticles at the atomistic level.

The melting process of nickel nanowires are simulated by using molecular dynamics with the quantum Sutten-Chen many-body force field. The wires studied were approximately cylindrical in cross-section and periodic boundary conditions were applied along their length; the atoms were arranged initially in a face-centred cubic structure with the [0 0 1] direction parallel to the long axis of the wire. The size effects of the nanowires on the melting temperatures are investigated. We find that for the nanoscale regime, the melting temperatures of Ni nanowires are much lower than that of the bulk and are linear with the reciprocal of the diameter of the nanowire. When a nanowire is heated up above the melting temperature, the neck of the nanowire begins to arise and the diameter of neck decreases rapidly with the equilibrated running time. Finally, the breaking of nanowire arises, which leads to the formation of the spherical clusters. r

Introducing hollow structures into metallic nanoparticles has become a promising route to improve their catalytic performances. A fundamental understanding of thermal stability of these novel nanostructures is of significance for their syntheses and applications. In this article, molecular dynamics simulations have been employed to offer insights into the thermodynamic evolution of hollow bimetallic core-shell nanoparticles. Our investigation reveals that for hollow Pt-core/Au-shell nanoparticle, premelting originates at the exterior surface, and a typical two-stage melting behavior is exhibited, similar to the solid ones. However, since the interior surface provides facilitation for the premelting initiating at the core, the two-stage melting is also observed in hollow Au-core/Pt-shell nanoparticle, remarkably different from the solid one. Furthermore, the collapse of hollow structure is accompanied with the overall melting of the hollow Pt-core/Au-shell nanoparticle while it occurs prior to that of the hollow Au-core/Pt-shell nanoparticle and leads to the formation of a liquid-core/solid-shell structure, although both of them finally transform into a mixing alloy with Au-dominated surface. Additionally, the existence of stacking faults in the hollow Pt-core/Au-shell nanoparticle distinctly lowers its melting point. This study could be of great importance to the design and development of novel nanocatalysts with both high activity and excellent stability.

Morphologies of gold nanoparticles play an important role in determining their chemical and physical (catalytic, electronic, optical, etc.) properties. Therefore, a fundamental understanding of the morphological stability is of crucial importance to their applications. In this article, we employed atomistic simulations to systematically investigate the structural and thermal stabilities of gold particles with eight representative nanoshapes, including single-crystalline and multiple-twinned structures. Our investigation has revealed that the truncated octahedron and the octahedron possessed the best structural stability, while the tetrahedron and the icosahedron did the worst. Further analyses have discovered different thermal stabilities and diverse melting behaviors in these particles. Especially, an inhomogeneous melting of the icosahedron was disclosed, and the relevant mechanism was elucidated.This study provides significant insight not only into the experimental preparation of gold nanoparticles but also into the design of gold nanostructures with both high catalytic activity and excellent stability.