Overheating and undercooling during melting and crystallization of metal nanoparticles

In analogy with macroscopic metal samples, crystallization of metal nanoparticles may occur appreciably below the thermodynamic melting temperature, Tm (this temperature depends on the particle size), while melting occurs at Tm. If the surface melting is suppressed, nanoparticles can be overheated during melting. We describe these effects by using the classical nucleation theory and assuming that the nucleation starts at the particle corners or edges. The corresponding undercooling or overheating temperature intervals are found to be about 0.1Tm for corners and 0.15Tm for edges. These values are, respectively, two and one and a half times smaller than that for macroscopic samples. Under certain conditions, crystallization and melting can be controlled by the propagation of the front of a new phase. The corresponding temperature interval is found to be very narrow (about 0.02Tm).