The purpose of this thesis has been to investigate the elastic properties of an fcc FeMg alloy with 10 at.% magnesium under high pressure. Recent research has shown that magnesium can be a possible candidate for light element impurities in the Earth’s inner core, something that was previously not considered possible because of the low miscibility of magnesium in iron at ambient pressure. Gaining knowledge about the composition of the Earth’s core can help us better understand such phenomena as seismic activity and the fluctuations of the Earth’s magnetic field. The elastic constants of the FeMg alloy was calculated using ab-initio methods based on Density Functional Theory. The Exact Muffin-Tin Orbitals method was used in conjunction with the Coherent Potential Approximation. The FeMg alloy was found to be overall considerably softer than pure iron, and the softening effect on the elastic constants was also found to increase with pressure. The results also showed that 10% Mg alloying increased the anisotropy with about 40% compared to pure iron.

<p>The purpose of this thesis has been to investigate the elastic properties of an fcc FeMg alloy with 10 at.% magnesium under high pressure. Recent research has shown that magnesium can be a possible candidate for light element impurities in the Earth’s inner core, something that was previously not considered possible because of the low miscibility of magnesium in iron at ambient pressure. Gaining knowledge about the composition of the Earth’s core can help us better understand such phenomena as seismic activity and the fluctuations of the Earth’s magnetic field.</p><p>The elastic constants of the FeMg alloy was calculated using ab-initio methods based on Density Functional Theory. The Exact Muffin-Tin Orbitals method was used in conjunction with the Coherent Potential Approximation.</p><p>The FeMg alloy was found to be overall considerably softer than pure iron, and the softening effect on the elastic constants was also found to increase with pressure. The results also showed that 10% Mg alloying increased the anisotropy with about 40% compared to pure iron.</p>

Many modern materials and material systems are layered. The properties related to layers are connected to interactions between atomic layers. In the present thesis, we introduce the interlayer potential (ILP), a novel model potential which fully describes the interaction between layers. The ILPs are different from the usual interatomic potentials which present interaction between atoms. We use the Chen-Möbius inversion method to extract the ILPs from ab initio total energy calculations. The so obtained ILPs can be employed to investigate several physical parameters connected with the particular set of atomic layers, e.g. surface energy, stacking fault energy, elastic parameters, etc. The interactions between the face centered cubic (fcc) (111) planes are described by two different ILPs. Using two close-packed model structures, namely the ABC stacking along the fcc ⟨111⟩ direction and AB stacking along the hcp ⟨0001⟩ direction, we demonstrate how these two ILPs are obtained via the Chen-Möbius method. Density function theory (DFT) is employed to generate the ILPs and also to compute the equilibrium structural properties of elemental metals Al, Ni, Cu, Ag, Au and Pd as well as of Pd-Ag random solid solutions. With the so established ILPs, we adopt the supercell method and the axial interaction model to calculate the stacking fault energy along the fcc ⟨111⟩ direction, including the intrinsic stacking fault energy, extrinsic stacking fault energy and twin stacking fault energy as well as the interactions between the intrinsic stacking faults. We find that the data derived from ILPs are consistent with those obtained in direct ab initio calculations. Along the fcc ⟨111⟩ direction, we study the surface energy and surface relaxation using the ILPs. The phonon dispersions are also described. We conclude that the interlayer potentials based on the Chen-M¨obius inversion technique may provide a new way to investigate the properties related to layers in layered materials. / <p>QC 20121101</p>