Resumen de Computational studies of thermal transport in functional oxides
This Thesis collects the computational works we have done in the field of condensed matter physics, focused on the thermal transport properties of the Lead Titanate (PbTiO3) and the Zinc Oxide (ZnO), both representative materials of many other insulating functional oxides. The first has been modeled using a second-principles potential, that is, a potential parameterized from first-principles calculations, which captures some quantum effects that can be relevant in the material. We have modeled the second one using the Buckingham's potential, a simple analytical expression that seems to describe the behavior of ZnO in a fairly approximate agreement with experiments.
In particular, we focus on how to modulate their thermal conductivity modifying their crystal lattice by means of an external electric field or pressure. Our studies have been always performed within the framework of Fourier's law, from two different techniques: performing Molecular Dynamics simulations, both at equilibrium and out-of-equilibrium, and solving the Boltzmann Transport Equation for phonons. Both techniques superbly combine, since while Boltzmann Transport Equation takes into account the quantum effects that intervene in the microscopic description of the system, but only up to the third order of the anharmonic scattering, Molecular Dynamics trajectories are classical but capture all scattering events, i.e., all orders of anharmonicity are included.
These studies also describe how phonons are affected when the crystal lattice of both oxides is altered, explaining which changes of their properties (frequency, velocity and mean free path) are relevant for the changes in thermal conductivity. Additionally, this work also present various applications in the field of phononics, laying the groundwork for the design of thermal switches and transistors.
