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Solid-solution precursor to melting in onion-ring Pd-Pt nanoclusters: a case of second-order-like phase change?
1LASIM, Université Claude Bernard Lyon I, Lyon, France. fcalvo@lasim.univ-lyon1.fr
Faraday Discussions
|May 2, 2008
Summary
Icosahedral palladium-platinum (Pd-Pt) clusters melt at lower temperatures than bulk materials. Smaller clusters exhibit a solid-solution phase before melting, indicating bulk behavior recovery at nanoscale.
Area of Science:
- Materials Science
- Computational Chemistry
- Thermodynamics
Background:
- Understanding the thermodynamic properties of nanoscale materials is crucial for developing new technologies.
- Alloy clusters exhibit unique melting behaviors distinct from their bulk counterparts.
Purpose of the Study:
- To investigate the thermodynamic behavior of icosahedral, multilayer palladium-platinum (Pd-Pt) clusters.
- To explore the melting dynamics and structural transitions in Pd-rich clusters of varying sizes.
Main Methods:
- Utilized parallel tempering Monte Carlo simulations.
- Introduced a preferential swapping trial move to enhance atom exchange efficiency.
- Studied 2-, 3-, and 4-shell Pd-rich clusters.
Main Results:
- Clusters melt at significantly lower temperatures than bulk Pd-Pt alloys.
- Smaller clusters undergo a solid-solution phase transition before melting, retaining their icosahedral structure.
- This transition exhibits characteristics similar to a second-order phase transition, analogous to the 3D Ising model.
- Larger clusters (4-layer) show a solid-solution core even at low temperatures (100 K).
Conclusions:
- Nanoscale Pd-Pt clusters display unique melting behaviors, deviating from bulk properties.
- The solid-solution phase is a key intermediate state in the melting process of smaller clusters.
- Bulk-like thermodynamic behavior is observed to emerge at very small cluster scales.
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