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

Abstract

Kinetic Monte Carlo (KMC) and graph searches show that proton conduction limiting barriers and trajectories in BaZr 0.875 Y 0.125 O 3 are affected by the presence of other protons. At 1000 K, KMC limiting conduction barriers increase from 0.39 eV to 0.45 eV as the proton number is increased. The proton-proton radial distribution begins to rise at 2 Å and peaks at 4 Å, which is half the distance expected, based on the proton concentration. Density functional theory (DFT) calculations find proton/proton distances of 2.60 and 2.16 Å in the lowest energy two-proton configurations. A simple average of the limiting barriers for 7-10 step periodic long range paths found via graph theory at 1100 K shows an increase in activation barrier from 0.32 eV to 0.37 eV when a proton is added. Both KMC and graph theory show that protons can affect each other's pathways and raise the overall conduction barriers.

Local structure and vibrational dynamics in indium-doped barium zirconate

“…In the present scenario involving 4 protons (x ¼ 4/8), it is reasonable to observe this effect to be even more preponderant. While our results are in full accordance with the results by Gomez et al 66 on the concept of extended distortions, we suggest that these distortions are, at least partially, dynamical rather than static at room temperature, as they span both the oxygen atom dynamics and the extended proton arrangement. Whatever the case, the concept of extended distortions is consistent with the coexistence of numerous local proton congurations and thus the apparent large inhomogeneous broadening of the vibrational spectra of 50In/BZO.…”

“…lower n(O-H) frequency, in a recent computational work on Y-doped BaZrO 3 . 66 This work, which was based on models with a single dopant (x ¼ 1/8) and two protons, suggested that the protons tend to pair, in agreement with previous results from Bork et al 67 on SrTiO 3 , and that the proton-proton vicinity affects the hydrogen bond strength. According to these works, the effect of one proton on another one is not a mere direct proton-proton interaction, but rather is driven by local lattice distortion.…”

Local Distortions and Dynamics in Hydrated Y-Doped BaZrO3

“… 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. These activation energies are closer to the values of 40.5 and 45.0 kJ mol –1 determined experimentally.…”

Recent progress in the experimental and theoretical studies on the barium zirconate proton conductors: A review

“…Furthermore, kinetic Monte Carlo (KMC) associated with DFT calculations has shown that proton conduction can be hampered by the presence of other protons [210], as suggested by calculation of proton transporting energy barriers at high temperature in doped BZO. It is relevant to mention that oxidation and hole conductivity can be affected by polaronic contribution in the doped state of BZO perovskite [175].…”