Melting-point depression by insoluble impurities: a finite size effect.
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.
Hock
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Fakultät für Physik, Universität Freiburg, Hermann-Herder-Strasse 3, 79104 Freiburg, Germany.
Straburg
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S
Haberland
H
H
v Issendorff
B
B
Aguado
A
A
Schmidt
M
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