The Impact of Nanoscale Percolation in Yttrium‐Doped BaZrO3 on the Oxygen Ion and Proton Conductivities: A Density Functional Theory and Kinetic Monte Carlo Study

Yttrium‐doped BaZrO3 is known for its high proton conductivity, making it an advanced energy material for various applications, like electrolyzers, fuel cells, or methane conversion cells. In the previous study, density functional theory (DFT) and kinetic Monte Carlo simulations (KMC) show that nanoscale percolation of Y ions enhances the proton mobility by providing fast migration pathways for protons. To investigate the general impact of nanoscale percolation on ionic conductivities, the same methods, DFT and KMC, are now used to calculate oxygen ion conductivity of Y‐doped BaZrO3. The results explain on a microscopic level why the macroscopic oxygen ion conductivity exhibits a higher activation energy than the proton conductivity, as known experimentally. They also show that nanoscale percolation pathways are not beneficial for oxygen ion conduction due to trapping of oxygen vacancies by single Y ions and blocking of their motion by nanoscale percolation of Y ions. Finally, the understanding and comparison of the microscopic jump processes of oxygen vacancies and of protons in acceptor‐doped BaZrO3 are used to propose a simple descriptor for the influence of a dopant on the ionic conductivities, of oxygen ions and of protons as well. This new descriptor allows an easy screening of various dopants. In Y‐doped BaZrO3, oxygen vacancies and protons are both trapped by Y. While the jumps of oxygen vacancies to nearest‐neighbor positions are blocked by Y, the jumps of protons are facilitated by Y. With increasing dopant fraction, nanoscale percolation of Y ions occurs, which is detrimental for oxygen ion conductivity while it is beneficial for proton conductivity.