Protons in Al doped BaZrO3 escape dopant traps to access long range proton conduction highways

A combination of electronic structure methods, graph theory, and kinetic Monte Carlo (KMC) shows that doping BaZrO3 with aluminum instead of yttrium at the Zr site changes the long range proton conduction pathways by altering local geometry. When the zirconium ion is replaced by the smaller aluminum ion, there is a small contraction which decreases the degree of octahedral tilting possible. The decreased octahedral tilting results in a greater contrast in energies close to the dopant and farther from it. The greater contrast leads to such high barriers to escape the dopant region that the most probable long range proton conduction pathways avoid the dopant region. KMC trajectories show long periods of proton trapping near the dopant followed by rare excursions away from it during which the proton accesses the high probability long range proton conducting pathways enabling long range conduction. In contrast, in yttrium doped systems where the barrier to get away from the dopant is lower, earlier work has shown that the probable long range proton conducting pathways include sections near the dopant.