Graph analysis of proton conduction pathways in scandium-doped barium zirconate.

Understanding the relationship between the acceptor dopant size and proton conductivity in barium zirconate, BaZrO, is important for maximizing efficiency in this promising fuel cell material. While proton conduction pathways with larger Y and smaller Al defects have been explored, proton pathways with Sc , a defect of comparable size to the replaced ion, have not been investigated using centrality measures, periodic pathway searches, and kinetic Monte Carlo (KMC). Centrality measures in BaScZrO highlight a trapping region by Sc and scattered high centrality regions on undoped planes. Connected long-range high centrality regions are found mainly in undoped planes for BaAlZrO and in the dopant planes for BaYZrO. The best long-range proton conduction periodic pathways in Al and Sc systems travel between dopant planes, while those for yttrium-doped BaZrO remained on dopant planes. KMC trajectories at 1000 K show long-range proton conduction barriers of 0.86 eV, 0.52 eV, and 0.25 eV for Al , Sc , and Y systems, respectively. Long-range periodic conduction highway limiting barrier averages correlate well with the connectivity of the most central regions in each system but ignore diffusion around the dopant and through other high centrality regions. BaScZrO shows an intermediate overall conduction barrier limited by trapping, which earlier experiments and simulations suggest that it can be mitigated with increased oxygen vacancy concentration.