Mechanical Properties of Amorphous B2O3 Nanopillars Under Compressive Loading : A Molecular Dynamics Study

Abstract

Oxide glasses are essential materials for modern life with numerous applications, yet their usage is often limited by their inherent brittleness. This fragility originates from their amorphous network structure, unlike metals, glasses lack dislocation slip mechanisms, resulting in catastrophic failure once peak stress is reached. However, recent studies have shown surprising microscale plasticity in amorphous aluminum oxide at room temperature. Boron oxide (B2O3) presents a unique case due to its planar network structure, which differs from the three-dimensional networks of most other oxide glasses. Understanding the mechanical behavior of such distinct network offers better insights into the fundamental mechanisms of plasticity in glass.

This thesis investigates the room temperature mechanical response of amorphous B2O3 nanopillars using classical molecular dynamics simulation. The results reveal that B2O3 nanopillars exhibit remarkable ductility, sustaining up to 0.5 strain without fracture or shear localization. The material demonstrates a smooth transition from linear elasticity to plastic flow, characterized by a low Young’s modulus (12 GPa) and ultimate strength (2.3 GPa). These properties are linked to the material’s specific structure, where the planar BO3 units of B2O3 act as rigid building blocks connected by flexible bridging oxygen atoms, resulting in a comparatively soft and compliant network. Structural analysis identifies a distinct two-stage mechanism for accommodating this large deformation. Initially, the network undergoes geometric compaction, densifying by about 11 % as the flexible B–O–B bonds bend to fold the structure into its own free volume. Subsequently, plasticity is driven by distributed bond switching. Over 70 % of atoms exchange neighbors during compression. These bond switching events allows the material to undergo local rearrangements allowing the material deform plastically