Unveiling hidden particle-level defects in glasses

Area of Science:

• Materials Science
• Condensed Matter Physics
• Computational Materials Science

Background:

• Crystalline defects are well-understood and impact mechanical properties.
• Structural disorder in glasses hinders direct particle-level defect identification.
• Low-frequency quasi-localised modes (QLMs) in glasses are linked to mechanical defects like shear transformation zones and soft spots.

Purpose of the Study:

• To identify the specific particle-level defect responsible for generating QLMs in glasses.
• To understand the relationship between these defects and mechanical anisotropy.
• To investigate the potential for controlling glass properties by manipulating these defects.

Main Methods:

• Utilized molecular dynamics simulations of two-dimensional glasses.
• Analyzed particle dynamics to identify defect structures.
• Investigated the impact of defect manipulation (pinning) on mechanical properties.

Main Results:

• Identified a "key-core" square of four particles as the source of primary QLMs.
• Observed a characteristic four-leaf deformation pattern around the key-core defect.
• Demonstrated that QLMs induce mechanical anisotropy, especially in nanoscale glasses.
• Showed that pinning key-core particles significantly reduces shear modulus anisotropy.

Conclusions:

• The "key-core" particle configuration acts as a localized, particle-level defect in glasses.
• These defects are directly responsible for generating QLMs and inducing mechanical anisotropy.
• The findings offer a new understanding of glass defects and potential applications in nanoscale materials.