Structural and spectroscopic study on bulk rare earth oxides for energy applications, under temperature and pressure effects

The present thesis work was carried out at the Physical Chemistry Labs of the Chemistry and Industrial Chemistry Department (DCCI) of the University of Genoa, working under the supervision of Professors Marcella Pani and Maria Maddalena Carnasciali who, together with Professor Cristina Artini and Professor Paola Costamagna, form the “Materials for Energy” research group. Part of the present investigation was also developed in collaboration with Doctor Francesco d’Acapito, beamline responsible at LISA (Linea Italiana per la Spettroscopia di Assorbimento x), at the European Synchrotron Radiation Facility (ESRF, Grenoble, FR), where the Candidate spent a period of four months, to learn the basis of X-rays Absorption Spectroscopy. The aim of the present work is to perform a comprehensive structural study on materials that can be used in solid oxides cells. In particular, the focus of the thesis is devoted to co-doped ceria systems, a family of widely investigated electrolytes, characterized by a high ionic conductivity (σ) at intermediate temperature (673-973 K). In these compounds, properly described by the formula Ce1-xRExO2-x/2 (RE= trivalent rare earth), the outstanding conductivity properties are strictly related to the structure, and in particular to the chemistry of defects. As a consequence, an in-depth structural study of these materials is a fundamental step to take, not only to better understand how the different structural features contribute to the ionic conductivity in the oxide, but also to evaluate the most suitable systems to be effectively used in solid oxides cells. For the structural characterization, different investigation techniques were employed, from the lab-scale ones, such as μ-Raman spectroscopy or impedance spectroscopy, to more sophisticated methods, which require the use of synchrotron light. The latter analyses were performed both at the ESRF facility and at the Elettra synchrotron (Trieste, IT).