Dopant arrangements in Y-doped BaZrO3 under processing conditions and their impact on proton conduction: a large-scale first-principles thermodynamics study

摘要

Y-doped BaZrO3 is an ion conductor under intense research for application in medium temperature solid oxide fuel cells. The conductivity is maximized at similar to 20% doping, and the decrease with further doping has often been attributed to the association effect, or the trapping of ionic charge carriers by the dopant. This seems like a reasonable conjecture since the dopant and carrier are charged in opposite polarities and should attract each other. However, at such high doping concentrations, many-body interactions between nearby dopants and carriers are likely to modify such a simple two-body attraction picture. Thus, in this work, we employ a large-scale first-principles thermodynamic sampling scheme to directly examine the configuration of dopants and charge-compensating defects at realistic doping concentrations under processing conditions. We find that although there is, indeed, a clearassociation effect at all doping concentrations examined, the magnitude of the effect actually decreases with increasing dopant concentration. We also find thatinteractions cannot simply be understood in terms of two-body Coulomb attraction and repulsion, highlighting the importance of many-body effects in understanding the defect chemistry in heavily doped oxides. Finally, we examine the dopant configurations and successfully explain the conductivity maximum based on a percolationvs.many-body trapping picture that has gained attention recently.