Structure and energetics of ceria-zirconia alloys: Insights from first principles in the ceria-poor region

We quantitatively investigate the structural and energetic properties of tetragonal, orthorhombic, and two monoclinic polymorphs of ceria-zirconia solid solutions in the ceria-poor region using first-principles density functional theory calculations. While Ce doping visibly leads to a lattice expansion due to longer Ce-O bonds, we find that phase stabilization is primarily governed by the chemical substitution energy, which can be qualitatively rationalized through the relative energies of pure ${\mathrm{ZrO}}_{2}$ and ${\mathrm{CeO}}_{2}$ structures. Local structural relaxations nevertheless play a role and depend primarily on the orientation and separation of Ce-Ce pairs. These effects can be interpreted within an iono-covalent screening model, which provides a physical picture of defect interactions and screening efficiency depending on the local defect environment. Our results offer microscopic insights into the mechanisms driving the phase stability and may guide the design of doped oxide materials with tailored properties.