SPECTROSCOPIC CHARACTERIZATIONS AND DFT SIMULATIONSOF CERAMIC MATERIALS:NANOSTRUCTURED ZIRCONIUM OXIDE AND ABO3 PEROVSKITES

Zirconium dioxide, ZrO2, is a widely studied material for its strength and fracture toughness, low thermal conductivity, ionic conductivity, chemical resistance, and biocompatibility. A broad range of applications derive from these properties, such as thermal-barrier coatings, wear resistance coatings, protective coating for optical mirrors and filters, high temperature fuel cells, oxygen detectors to catalyst supports, as well as biomedical and tissue engineering applications. This work is devoted to the characterization of nanostructured zirconia thin film in view of two specific applications: as catalytic support for Dry Reforming Methane (DRM) and as an electrolyte Solid Oxide Fuel Cell (SOFC). For these applications, the cubic/tetragonal phase demonstrates a better performance than the monoclinic phase. Moreover, the use of nanostructures could improve the catalytic activity and reduce the working temperature of SOFC from 800°C to 400°C. I have characterized nanostructured zirconium dioxide thin films synthesized by Supersonic Cluster Beam Deposition (SCBD) after thermal treatments using X-Ray Photoelectron Spectroscopy (XPS) and X-ray Powder Diffraction (XRPD). With these technique, it is possible to determine the surface and crystal phase evolution after the annealing process. The results indicate that the evolution mainly depends on the environmental condition in which the annealing is carried out. Moreover, I have simulated bulk zirconium dioxide in the tetragonal and monoclinic phase with different oxygen vacancies concentration. The calculations give a possible stabilization of the bulk zirconia in the tetragonal phase at room temperature that is solely due to oxygen vacancies. I have also applied a simple confinement model to determine the critical size for a film and for nanograin: the stable crystal phase at room temperature is the tetragonal phase. The simulated data are in good agreement with the experimental one. I also characterized by XPS two perovskite materials, LSCF and BSCF, used as a Mixed Ionic-Electronic Membrane (MIEC), in order to determine which one is more stable in working conditions; the LSCF membrane seems more stable than BSCF. This information can be use in the future to develop an SOFC with nanostructured zirconia thin film as an electrolyte and LSCF membrane as a cathode in an SOFC.