The Structures And Melting Behaviors Of Binary Alloy Nanoclusters

Over the past years, alloy clusters have raised great interests, most attentions have been paid on those with small sizes, and their melting behaviors are not well studied. In this thesis, by employing the Molecular Dynamic method, we have studied the structures and melting natures of Al-Ga binary alloy clusters. We obtained some common melting behaviors, and the structural characters, as well as their change with sizes and concentrations.According to our studies, we found that Ga atoms would segregate to the surface of the clusters and form the core-shell structures. The reason lies on:1) the size of Ga atoms is quite larger than that of Al atoms; 2) the surface energy of Ga atoms is a bit smaller than that of Al atoms. The inner structures of the clusters are closed related to the concentration of Ga atoms. If the amount of Ga atoms is quite small, there is a tendency to form a pure core consisted of Al atoms only. And the content of Ga atoms in cores will increase with the increase of the total concentration of Ga atoms in clusters. As the concentration of Ga atoms is fixed, a maximum number of Al atoms to form a critical cluster with pure core of Al atoms is also obtained.The structures of the Al-Ga clusters have strong effects on the melting behaviors. The melting processes begin from the surface of the clusters. Since Ga atoms cover the surfaces and form the shells, the surface melting stage is actually the melting of Ga atoms. The melting temperatures of surface melting will increase with the increase of the content of Ga atoms of the clusters. Since the melting temperature of Ga atoms is very low, there will be a large temperature difference between the surface melting and the complete melting. If the cluster has a pure core of Al atoms, the complete melting temperatures will come to very close. And it will decrease with the increase of the concentration of the Ga atoms in core.When the clusters are completely melted, the structures of the liquid clusters are similar to those of the solid ones. That is, the pure core of Al atoms can be preserved.