Centrality measures highlight proton traps and access points to proton highways in kinetic Monte Carlo trajectories

Abstract

A centrality measure based on the time of first returns rather than the number of steps is developed and applied to finding proton traps and access points to proton highways in the doped perovskite oxides: AZr 0.875 D 0.125 O 3 , where A is Ba or Sr and the dopant D is Y or Al. The high centrality region near the dopant is wider in the SrZrO 3 systems than the BaZrO 3 systems. In the aluminum-doped systems, a region of intermediate centrality (secondary region) is found in a plane away from the dopant. Kinetic Monte Carlo (kMC) trajectories show that this secondary region is an entry to fast conduction planes in the aluminum-doped systems in contrast to the highest centrality area near the dopant trap. The yttrium-doped systems do not show this secondary region because the fast conduction routes are in the same plane as the dopant and hence already in the high centrality trapped area. This centrality measure complements kMC by highlighting key areas in trajectories. The limiting activation barriers found via kMC are in very good agreement with experiments and related to the barriers to escape dopant traps. C 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License. [http://dx

Effects on the Proton Conduction Limiting Barriers and Trajectories in BaZr0.875Y0.125O3 Due to the Presence of Other Protons

“…Let us consider the effect of the applied field in more detail. As in our earlier single proton work, 45) the dopant defect acts as a trap for the proton. Occasionally, the trap is escaped through a long range limiting barrier which is most often an intraoctahedral transfer and less often a rotation.…”

“…Graph pathway searches for periodic pathways lead to more direct pathways than KMC trajectories and often have lower limiting barriers. 44,45) The advantage of having done DFT calculations in the presence of two protons was the revelation that the probe proton benefits from the lattice distortion that the excess proton introduced.…”

Local Distortions and Dynamics in Hydrated Y-Doped BaZrO3

“…The values calculated here are in the same range as the activation energy of 24.1 kJ mol –1 reported in the computational work of Gomez et al in which no yttrium is present and thus no trapping can occur. 38 Kinetic Monte Carlo (KMC) simulations, which simulated proton dynamics using 96 binding sites with a 12.5% dopant concentration, have predicted activation energies of 38 kJ mol –1 for a single proton 45 and 43 kJ mol –1 when eight protons were included in the simulation. 46 In these simulations, the protons spend a significant amount of time in Y–OH–Z sites but travel between these sites through perpendicular and planar sites.…”

Paradigms of frustration in superionic solid electrolytes

“…The barriers show a surprisingly broad range from ultrafast, liquid-like flow ( ) to very slow, solid-like hops ( approaching 0.7 eV). The long tail at higher activation barriers is particularly notable, since it represents local spatiotemporal zones that are effectively frozen [ 126 ]. Sites in this region are symmetrically identical to the fast-diffusing sites, yet dynamical fluctuations in the cation or anion sublattice cause some regions to be temporarily far more conducive to ion hopping than others.…”