Investigating the Al/Si mixed site occupancy in the β-AlFeSi phase

Area of Science:

• Materials Science
• Computational Materials Science
• Thermodynamics

Background:

• The β-AlFeSi phase exhibits complex mixed site occupancy of aluminum (Al) and silicon (Si) atoms.
• Accurate thermodynamic descriptions are crucial for understanding and predicting material behavior.
• Existing sublattice models for β-AlFeSi may contain inaccuracies in their thermodynamic descriptions.

Purpose of the Study:

• To investigate the mixed site occupancy of Al and Si in the β-AlFeSi phase.
• To develop and validate an accurate thermodynamic model for the β-AlFeSi solid solution.
• To compare the predictive accuracy of different sublattice models.

Main Methods:

• Calculated enthalpies of formation for 64 ordered end-member structures using Density Functional Theory (DFT).
• Determined heat capacities via a Debye model, incorporating elastic constants and equation of state.
• Utilized Compound Energy Formalism (CEF) for configurational entropy to calculate site occupation fractions at 300 K and 938 K.

Main Results:

• Derived the enthalpy of mixing for the solid solution across a wide range of compositions.
• Calculated Gibbs free energies for all end-members.
• Identified a novel, accurate sublattice model by merging specific Al/Si sites, outperforming commonly accepted models.

Conclusions:

• The proposed simple and accurate sublattice model significantly improves the thermodynamic description of the β-AlFeSi solid solution.
• Commonly accepted sublattice models in the literature generate considerable errors.
• The study provides crucial data for quantifying chemical ordering and understanding Al/Si site occupancy in β-AlFeSi.