A theoretical study of the influence of dopant concentration on the hydration properties of yttrium-doped barium cerate

Yttrium-doped barium cerate (BCY) exhibits among the highest proton conductivities of perovskite materials, but a detailed understanding of BCY hydration properties and their relationship to material structure is not yet available. In this paper, density functional theory (DFT) was used to investigate how dopant concentration influences the hydration properties of BCY. Consistent with experimental results, the hydration enthalpy was found to become more favorable with increasing dopant concentration. A Bader charge analysis confirmed that increasing the doping level increases oxygen basicity, stabilizing protonic defects. A statistical thermodynamic model was developed to predict BCY hydration entropy. The model is shown to be consistent with previously reported experimental results, indicating that increased dopant concentrations lead to more negative hydration entropies. Finally, the in silico enthalpy data and a priori derived entropy model was used to develop an equation that describes the extent of material hydration, which compared well to experimental data. This work demonstrates a method to predict hydration behavior in this class of ionic conducting materials using solely first-principles techniques.