Vacancies and interstitials in yttrium

Area of Science:

• Materials Science
• Condensed Matter Physics
• Computational Materials Science

Background:

• Understanding point defects is crucial for predicting material properties.
• Metallic yttrium (Y) is an important material with limited data on defect properties.
• First principles simulations offer a powerful tool to investigate atomic-scale phenomena.

Purpose of the Study:

• To calculate formation energies and migration barriers of point defects in yttrium.
• To elucidate the role of vacancies, divacancies, and interstitials in yttrium's self-diffusion.
• To compare simulation results with experimental data and general trends in hexagonal close-packed (hcp) metals.

Main Methods:

• Density Functional Theory (DFT) calculations were employed.
• Simulations focused on self point defects: vacancies, divacancies, and single interstitials.
• Energetic properties (formation energies, migration barriers, binding energies) were computed.

Main Results:

• High vacancy formation energy (~1.8 eV) and moderate migration barriers (~0.65 eV) in yttrium.
• Divacancies exhibit a binding energy of ~0.2 eV and lower migration barriers, indicating their role in mass transport.
• The basal octahedral configuration is the stable interstitial site, with isotropic diffusion barriers (~0.4 eV).

Conclusions:

• Calculated defect properties align with experimental self-diffusion data for yttrium.
• Divacancies are identified as key mediators of mass transfer in yttrium.
• The findings are consistent with trends observed in hcp metals with a specific c/a ratio.