| In this thesis, I present results and analyses of first principles calculations based on Density Functional Theory (DFT) to examine the structural, electronic and lattice properties of two complex oxide systems: the misfit-layered thermoelectric Ca3Co4O9 (CCO) and a polar interface containing the solid oxide electrolyte LaGaO 3 (LGO). In Chapter 1, I present a general introduction and the motivation for the study of these systems. This is followed by a brief summary of the fundamental ideas in DFT and the different theoretical methods employed in my calculations in Chapter 2. In Chapter 3, I present results and discussion related to the electronic structure of CCO calculated by means of increasing order Fibonacci approximants. In Chapter 4, I focus on the lattice and thermal properties of this material, in particular, the calculation of the thermal conductivity by combining first principles results with the Boltzmann transport equation. In Chapter 5, I propose and analyze the computational design of a polar interface in order to increase the ionic conductivity of LGO. Finally, in Chapter 6 I present a summary and the conclusions of my studies. |
