Self-diffusion in MgO--a density functional study.

Area of Science:

• Computational Materials Science
• Solid State Chemistry
• Defect Physics

Background:

• Magnesium oxide (MgO) serves as a model ionic compound for studying diffusion mechanisms.
• Understanding self-diffusion is crucial for predicting material properties and performance in various applications.
• Defects, such as Schottky defects and divacancies, significantly influence ionic transport in oxides.

Purpose of the Study:

• To investigate the self-diffusion mechanisms of magnesium (Mg) and oxygen (O) in magnesium oxide using first-principles calculations.
• To determine the formation energies, entropies, and migration rates of relevant defects.
• To compare computational predictions with experimental diffusion data.

Main Methods:

• Density functional theory (DFT) calculations were employed to determine defect formation energies and entropies.
• Total energy and phonon calculations in supercell configurations were utilized.
• Transition state theory, incorporating static migration energies and phonon-derived frequency factors, estimated defect migration rates.

Main Results:

• Calculations confirm that Mg self-diffusion in nominally pure MgO occurs extrinsically via single vacancies.
• Oxygen (O) self-diffusion is predominantly intrinsic and mediated by divacancies.
• Computational results show excellent agreement with experimental data for O diffusion, while Mg diffusion rates are underestimated by a factor of 5-10.

Conclusions:

• The study validates the established understanding of Mg and O self-diffusion mechanisms in MgO.
• Discrepancies in Mg diffusion rates highlight potential areas for further theoretical and experimental investigation.
• DFT provides a robust framework for understanding defect-mediated diffusion in ionic materials.