The interplay of structure and dynamics at grain boundaries

Area of Science:

• Materials Science
• Computational Materials Science
• Solid-State Physics

Background:

• Grain boundaries significantly influence material properties, but their atomic structure and diffusion mechanisms are often obscured by thermal motion.
• Traditional molecular dynamics methods struggle to isolate the distinct contributions of structural arrangements and atomic movements at grain boundaries.

Purpose of the Study:

• To develop and apply a novel molecular simulation method, the inherent structure approach, for analyzing atomic structure and diffusion at grain boundaries.
• To accurately calculate grain boundary diffusion coefficients in polycrystalline magnesium oxide (MgO) without arbitrary assumptions.
• To elucidate the elementary steps governing atomic diffusion processes within grain boundaries.

Main Methods:

• Employed the inherent structure approach, mapping molecular dynamics configurations to potential energy minima (inherent structures).
• Decomposed atomic dynamics into displacements within inherent structures and transitions between them.
• Applied the method to polycrystalline MgO, identifying grain boundary atoms based on undercoordination in their inherent structures.

Main Results:

• The inherent structure approach provided a clear atomic-level picture of grain boundaries, distinct from thermal fluctuations.
• Calculated grain boundary diffusion coefficients for MgO were consistent with experimental estimates.
• Identified vacancy hops as the dominant diffusion mechanism in MgO grain boundaries, with concurrent motion of neighboring atoms.

Conclusions:

• The inherent structure approach is a powerful tool for understanding grain boundary structure and atomic diffusion in materials.
• This methodology enables accurate, assumption-free calculation of grain boundary diffusion coefficients.
• The study elucidated the specific atomic mechanisms driving diffusion in MgO grain boundaries.