The effect of one proton on the possible pathways of another proton in yttrium-doped barium zirconate
Hoang, Minh Tam
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Proton conduction is a crucial property of fuel cell electrolytes. Unlike oxide-ion conductivity in oxide-ion conductors, proton conductivity occurs at a lower temperature (less than 600◦C), enhancing material stability and facilitating heat recovery for a variety of applications. Perovskite structure, ABO3 is one of the structure families that observe proton diffusion and proton conductivity, making it a potential candidate for solid-state proton conductors. Previous works studied the proton conduction in 12.5% Y-doped BaZrO3 system with multiple protons and found that the incorporation of protons into the system affects backbone distortion, kinetic energy barriers, and proton trajectories. In this study, we investigate the effect of one proton on the pathways of another proton in the same system but with larger dimension. The ab initio method is utilized to obtain the total electronic energy for each configuration using Density Functional Theory and the Perdew–Burke–Ernzerhof functional. The lowest-energy configuration results from the structure in which two protons are in closest proximity to the dopant. We notice that the distortion induced by protons only affects backbone structure at the local level in the large system. However, the presence of two protons completely alters the tilting pattern in the smaller system. The Nudged Elastic Band method is applied to the perovskite configurations to find the conduction pathways between two proton binding sites. As a result, we found that there are no contractions of the intra-octahedral and inter-octahedral O-O distances along the proton pathway with rotation movement. However, both intra-octahedral and inter-octahedral transfers cause changes in lattice distortion and witness intermediate minima between initial and final binding sites, suggesting more complex pathways. Also, we notice that a full inter-octahedral transfer has a tendency to break down into two consecutive intra-octahedral transfer along the Nudged Elastic Band pathways, suggesting the prioritization of intra-octahedral transfers in the proton trajectories.
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