Self-diffusion mechanisms based defect complexes in MoSi₂.

Area of Science:

• Materials Science
• Solid State Physics
• Computational Materials Science

Background:

• Molybdenum disilicide (MoSi2) is a vital transition metal silicide known for excellent electrical conductivity and oxidation resistance.
• High-temperature diffusion in MoSi2 coatings is critical for material degradation, yet its atomic mechanism remains poorly understood.
• Previous theoretical studies on defect formation energy alone did not fully align with experimental self-diffusion data.

Purpose of the Study:

• To elucidate the microscopic diffusion mechanisms of Molybdenum (Mo) and Silicon (Si) atoms within MoSi2.
• To investigate the influence of temperature-dependent vibrational contributions on defect formation free energy.
• To identify the role of defect aggregation and complex formation in atomic diffusion.

Main Methods:

• Utilizing density functional theory (DFT) for atomic-level simulations.
• Employing the climbing image nudged elastic band (CI-NEB) method to calculate migration barriers.
• Analyzing electronic structures to understand defect migration pathways.

Main Results:

• Temperature-dependent vibrations significantly impact defect formation free energy.
• Isolated point defects in MoSi2 tend to form defect complexes that mediate diffusion.
• Silicon diffusion is primarily driven by intrasublattice jumps of nearest-neighbor silicon vacancies.
• Mo atom mobility is enhanced by the disruption of Mo-Si covalent bonds and formation of weak metal bonds by Mo antisites, leading to lower migration barriers.
• Calculated results align with experimental findings, indicating vacancy complex-mediated and antisite-assisted jumps dominate Mo diffusion.

Conclusions:

• Silicon vacancy-based defect complexes are identified as the primary mediators for Mo atom self-diffusion in MoSi2.
• The study provides crucial insights into the link between atomic diffusion mechanisms and macroscopic material behavior.
• This research lays the foundation for developing improved high-temperature MoSi2-based coating materials.