Reversed size-dependent stabilization of ordered nanophases.

Area of Science:

• Materials Science
• Nanotechnology
• Physical Chemistry

Background:

• Nanoparticle stability often increases with size.
• Ordered phases in nanomaterials are crucial for their properties.
• Understanding size-dependent phase stability is key for designing advanced materials.

Purpose of the Study:

• To investigate the phase stability of L1₁ ordered AgPt nanoparticles.
• To determine the influence of particle size on the formation of the defect-free L1₁ phase.
• To elucidate the mechanisms governing phase stabilization in small nanoparticles.

Main Methods:

• Utilized a multiscale modelling approach.
• Employed full-DFT global optimization calculations.
• Applied atomistic modelling techniques.

Main Results:

• Demonstrated that smaller AgPt nanoparticles (≤2.5 nm) stabilize the defect-free L1₁ phase better than larger ones.
• Observed that larger nanoparticles exhibit phase domain fragmentation and faults.
• Identified a segregated silver monolayer (Ag-skin) as the driving force for L1₁ phase formation in small nanoparticles.
• Found that the Ag-skin induces internal stress in larger nanoparticles, limiting the ordered phase domain size.

Conclusions:

• The study presents a counterexample to the common trend of increasing stability with nanoparticle size.
• The Ag-skin formation is critical for stabilizing the L1₁ phase in small AgPt nanoparticles.
• Internal stress due to the Ag-skin limits the critical size for the stable L1₁ phase in AgPt nanoparticles.