A Theoretical Study of Doping and the Hydration Process of Barium Zirconate

Abstract

In this thesis we give a brief review of Kohn-Sham density functional theory and different exchange-correlation functionals. The BaZrO3 lattice constant is obtained and the ground state considered. We examine the electronic structure using PBE and PBE0. PBE0 provides a greatly improved density of states. We consider the use of H2O as a reference molecule for O which reduces error due to PBE’s description of O2 binding energy by 40%. We compare the local environment around an oxygen vacancy in BaZrO3 to that in SrTiO3 and examine the expansion due to dopant atoms and hydration in BaZrO3. Then follows a comparative study between the PBE and PBE0 description of oxidation and hydration in BaZrO3. We calculate the reaction enthalpies, equilibrium rate constants and defect concentration profiles most relevant for the reactions. The PBE0 and PBE oxidation enthalpy are positive and negative respectively which leads to very different rate constants and concentration profiles. However, neither one of the enthalpies seem to contradict experimental evidence of increased electrical conductivity at elevated temperature.