title: Melting-point depression by insoluble impurities: a finite size effect.
abstract: Melting-point depression by soluble impurities is an entropy-driven phenomenon. Studying partially oxidized free sodium nanoparticles, we found an additional mechanism, which is caused by insoluble impurities. Oxidization of sodium clusters with 135-192 atoms by a single oxygen molecule causes a melting-point depression of 17+/-6 K; additional oxygen amplifies the effect. This is in contrast to the behavior of bulk sodium, where the melting point does not change upon partial oxidization. First-principles density functional theory calculations reveal the interaction between the pure and the oxidized part of the cluster to be responsible for the effect. There is more structural freedom in a liquid cluster to optimize the interface between the two parts. This stabilizes the liquid phase and causes the observed, cluster-specific melting-point depression.
authors.affiliation: Fakultät für Physik, Universität Freiburg, Hermann-Herder-Strasse 3, 79104 Freiburg, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Hock
authors.forename: S
authors.initials: S
authors.lastname: Straburg
authors.forename: H
authors.initials: H
authors.lastname: Haberland
authors.forename: B
authors.initials: B
authors.lastname: v Issendorff
authors.forename: A
authors.initials: A
authors.lastname: Aguado
authors.forename: M
authors.initials: M
authors.lastname: Schmidt