title: Crystal growth nucleation and Fermi energy equalization of intrinsic spherical nuclei in glass-forming melts.
abstract: The energy saving resulting from the equalization of Fermi energies of a crystal and its melt is added to the Gibbs free-energy change ΔG2lsassociated with a crystal formation in glass-forming melts. This negative contribution being a fraction εls(T) of the fusion heat is created by the electrostatic potential energy -U0resulting from the electron transfer from the crystal to the melt and is maximum at the melting temperatureTmin agreement with a thermodynamics constraint. The homogeneous nucleation critical temperatureT2, the nucleation critical barrier ΔG2ls∗/kBTand the critical radiusR∗2lsare determined as functions of εls(T). In bulk metallic glass forming melts, εls(T) andT2only depend on the free-volume disappearance temperatureT0l, and εls(Tm) is larger than 1 (T0l>Tm/3); in conventional undercooled melts εls(Tm) is smaller than 1 (T0l>Tm/3). Unmelted intrinsic crystals act as growth nuclei reducing ΔG2ls∗/kBTand the nucleation time. The temperature-time transformation diagrams of Mg65Y10Cu25, Zr41.2Ti13.8Cu12.5Ni10Be22.5, Pd43Cu27Ni10P20, Fe83B17and Ni melts are predicted using classic nucleation models including time lags in transient nucleation, by varying the intrinsic nucleus contribution to the reduction of ΔG2ls∗/kBT. The energy-saving coefficient εnm(T) of an unmelted crystal of radiusRnmis reduced whenRnm≪R∗2ls; εnmis quantified and corresponds to the first energy level of one s-electron moving in vacuum in the same spherical attractive potential -U0despite the fact that the charge screening is built by many-body effects.
authors.affiliation: Centre National de la Recherche Scientifique, Consortium de Recherches pour l'Emergence de Technologies Avancées, BP 166, 38042-Grenoble Cedex 09, France.
authors.forename: Robert F
authors.initials: RF
authors.lastname: Tournier
keywords: Fermi energy effects; crystal nucleation; glass-forming melts; intrinsic growth nuclei; metallic glasses; unmelted intrinsic crystals