Melting, premelting, and structural transitions in size-selected aluminum clusters with around 55 atoms

Heat capacities have been determined for unsupported aluminum clusters, Al-49(+)- Al-63(+), from 150 to 1050 K. Peaks in the heat capacities due to melting occur between 450 and 650 K ( well below the bulk melting point of 933 K). The peaks for Al-51(+) and Al-52(+) are bimodal, suggesting the presence of a premelting transition where the surface of the clusters melts around 100 K before the core. For clusters with n> 55 the melting temperatures suddenly drop, and there is a dip in the heat capacities due to a transition between two solid forms before the clusters melt.