Melting of Pb clusters without free surfaces

Melting behaviors of Pb clusters without free surfaces have been studied us ing molecular dynamics and the Sutton-Chen (SC) potential. Two Pb clusters (Pb-N, with N= 201 and 249) are selected and each of them has been embedded in the core of an Al-4033 cubo-octahedron, but with different orientation relationship with Al coatings. For the Pb-201 cluster, where a parallel cub e-cube relationship exists with the Al lattice, semicoherent interfaces can be formed and the core can be superheated up to 750 K, in comparing to the equilibrium melting point of 615+/- 10 K for bulk Pb predicted using the S C potential. On further elevating the temperature, a simultaneous melting o f both the Pb core and the outer Al coating will occur. For the Pb-249 clus ter without a parallel orientation relationship with Al, no effective semic oherent interface can be formed, and the core premelts at about 500 K witho ut breaking the crystalline structure of Al shells. The melting point of th e Pb inclusions can be predicted using thermodynamic relations. For differe nt Pb-Al interfaces, two melting mechanisms exist: one is the homogeneous m elting which leads to a melting point elevation and the other is the hetero geneous melting which can induce a melting point depression. [S0163-1829(99 )09625-3].