What should the density of amorphous solids be?

Area of Science:

• Materials Science
• Condensed Matter Physics
• Computational Chemistry

Background:

• Amorphous and crystalline solids exhibit density differences, typically 10%-15% for organic/inorganic materials but <5% for metallic alloys.
• Geometric models of atomic packing explain density variations in glasses but not metallic alloys.
• The small density difference in metallic alloys suggests changes in interatomic separations and atomic volumes.

Purpose of the Study:

• To investigate the hypothesis that merging orbitals cause reduced atomic volumes in amorphous metallic alloys.
• To test the applicability of standard geometric packing models to amorphous metallic alloys.
• To determine the relationship between interatomic distances and coordination in metallic systems.

Main Methods:

• Literature survey of amorphous and crystalline solid densities.
• Quantum density functional theory (DFT) computations.
• Analysis of ordered and irregular aluminum clusters.

Main Results:

• DFT computations revealed decreasing interatomic distances with decreasing coordination in aluminum clusters.
• Standard geometric models significantly underestimate the densities of amorphous metallic alloys.
• The findings support the hypothesis of reduced atomic volumes in amorphous metals.

Conclusions:

• The density of amorphous metallic alloys is influenced by variations in interatomic separations, not just packing geometry.
• Quantum mechanical effects, such as orbital merging, play a crucial role in determining metallic glass densities.
• Geometric models alone are insufficient for accurately predicting amorphous metallic alloy densities.