Intrinsic defects in and electronic properties of θ-Al13Fe4: an ab initio DFT study

theta-Al13Fe4 exhibits a rich variety of crystal physics. It contains twenty crystallographically different atomic species with a diversity of chemical coordination. An understanding of its structural and physical properties is a prerequisite for controlling its formation and its use. Here we investigate systematically the intrinsic defects in theta-Al13Fe4 using a first-principles density-functional theory method. The calculations reveal that among the various intrinsic defects it is energetically favourable for Fe substitution of Al but on just three of the fifteen Al sites. This results in a new structural model, Al68Fe24(Al, Fe)(4)(IX)(Al, Fe)(2)(VII)(Al, Fe)(4)(V) (the Roman numerals represent the Al sites) which updates the thermodynamic model, currently in use, which is associated with the formation of vacancies on some of the Al sites. The calculations demonstrate that the addition of Fe induces magnetism which gives rise to clustering. The calculations provide the dependence of the lattice parameters on Fe concentration and explain the experimental data in the literature. The information obtained here provides insight into the formation and properties of theta-Al13Fe4 and its role in the solidification of Al alloys, in determination of the microstructure and related mechanical properties of the products, and in catalysis for organic reactions.