Oxygen transport in rare-earth oxide (RE₂O₃) doped CeO₂ with fluorite structure has attracted considerable attention owing to both the range of practical usage (e.g., fuel cells, sensors, etc.) and the fundamental fascination of fast oxide ion transport in crystalline solids. Using density-functional theory, we have calculated the formation energies of point defects and their migration properties in RE₂O₃ doped CeO₂(RE = Sc, Y, La, Nd, Sm, Gd, Dy, and Lu). The calculated results show that oxygen vacancies are the dominant defect species obtained by RE³⁺ doping. They form associates with the RE³⁺ ions, and the corresponding defect association energy is a strong function of the ionic radii of the RE³⁺ dopants. The migration of an oxygen vacancy was investigated using the nudged elastic band method. The lowest activation energy for oxygen vacancy hopping is obtained for a straightforward migration path between two adjacent oxygen sites. The migration energy of an oxygen vacancy also strongly depends on the ionic radii of the neighbouring dopant cations. Accordingly, we have identified two factors that affect the oxygen vacancy migration; (1) trapping (or repelling) of an oxygen vacancy at the NN site of the RE³⁺ dopant, and (2) reduction (or enlargement) of the migration barrier by RE³⁺ doping. These findings provide insight for atomistic level understanding of ionic conductivity in doped ceria and would be beneficial for optimizing ionic conductivity.

For the first time, the high entropy perovskites from La_1−xSrx(Co,Cr,Fe,Mn,Ni)O₃₋δ(x= 0, 0.1, 0.2, 0.3, 0.4 and 0.5) series are documented to possess attractive properties as a candidate air electrode material for Solid Oxide Fuel Cells (SOFCs).

The intrinsic point defects of $$\beta${}$-${\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ are investigated using density functional theory. We have chosen two different exchange-correlation potentials: the generalized gradient approximation (GGA) and a hybrid potential (HSE06). Defect formation energies were determined taking into account finite-size effects. Schottky, anti-Frenkel, and Frenkel energies have been extracted for $T=0$ K. We calculate formation entropies for an oxygen and a gallium vacancy and determine the Gibbs energy of Schottky disorder. Furthermore, we investigate the defect concentrations as a function of the oxygen partial pressure. The obtained purely intrinsic defect concentrations for charged defects are very small and result in a $p{\mathrm{O}}_{2}$ dependence of the electron concentration of $[{\mathrm{e}}^{$'${}}]$\sim${}$ $p{\mathrm{O}}_{2}^{$-${}1/6}$, whereas experimentally $[{\mathrm{e}}^{$'${}}]$\sim${}$ $p{\mathrm{O}}_{2}^{$-${}1/4}$ is found. So we assume that, experimentally, a small unintentional donor doping is unavoidable. A small extrinsic donor concentration $[{\mathrm{D}}^{\ifmmode\cdot\else\textperiodcentered\fi{}}]$ $=$ 10${}^{18}$ cm${}^{$-${}3}$ (10 ppm) changes the electron concentration to $[{\mathrm{e}}^{$'${}}]$\sim${}$ $p{\mathrm{O}}_{2}^{$-${}1/4}$ and gives an activation energy of the conductivity $$\sigma${}$ of 1.7 eV in good agreement to experimental values. So we propose as majority disorder $3[{\mathrm{V}}_{\mathrm{Ga}}^{$'${}$'${}$'${}}]$ $=$ $[{\mathrm{D}}^{\ifmmode\cdot\else\textperiodcentered\fi{}}]$ with electrons being minority defects.

Materials with high oxygen ion conductivity and low electronic conductivity are required for electrolytes in solid oxide fuel cells (SOFC) and high-temperature electrolysis (SOEC). A potential candidate for the electrolytes, which separate oxidation and reduction processes, is rare-earth doped ceria. The prediction of the ionic conductivity of the electrolytes and a better understanding of the underlying atomistic mechanisms provide an important contribution to the future of sustainable and efficient energy conversion and storage. The central aim of this paper is the detailed investigation of the relationship between defect interactions at the microscopic level and the macroscopic oxygen ion conductivity in the bulk of doped ceria. By combining ab initio density functional theory (DFT) with Kinetic Monte Carlo (KMC) simulations, the oxygen ion conductivity is predicted as a function of the doping concentration. Migration barriers are analyzed for energy contributions, which are caused by the interactions of dopants and vacancies with the migrating oxygen vacancy. We clearly distinguish between energy contributions that are either uniform for forward and backward jumps or favor one migration direction over the reverse direction. If the presence of a dopant changes the migration energy identically for forward and backward jumps, the resulting energy contribution is referred to as blocking. If the change in migration energy due to doping is different for forward and backward jumps of a specific ionic configuration, the resulting energy contributions are referred to as trapping. The influence of both effects on the ionic conductivity is analyzed: blocking determines the dopant fraction where the ionic conductivity exhibits the maximum. Trapping limits the maximum ionic conductivity value. In this way, a deeper understanding of the underlying mechanisms determining the influence of dopants on the ionic conductivity is obtained and the ionic conductivity is predicted more accurately. The detailed results and insights obtained here for doped ceria can be generalized and applied to other ion conductors that are important for SOFCs and SOECs as well as solid state batteries.