Insights Into Defect Arrangements in Y-Doped BaZrO3 From Large-Scale First-Principles Thermodynamic Sampling: Association, Repulsion, Percolation, and Trapping

Y-doped BaZrO₃ is an ion conductor under intense research for application in medium temperature solid oxide fuel cells. The conductivity is maximized at ~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 clear Y_Zr – V_O association effect at all doping concentrations examined, the magnitude of the effect actually decreases with increasing dopant concentration. We also find that Y_Zr–Y_Zr and V_O –V_O interactions 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 percolation vs. trapping picture that has gained attention recently.