Influence of Ce polarons on grain boundary space-charge in proton conducting Y-doped BaCeO.

Defect segregation and space-charge formation were investigated for a (0 2 1)[1 0 0] symmetric tilt grain boundary in Y-doped BaCeO3. Density functional theory calculations according to the PBE+U formalism were used to calculate segregation energies for protons, oxygen vacancies and Y-acceptor dopants from the bulk to the grain boundary core. Defect concentration and potential profiles across the grain boundary were obtained from thermodynamic space-charge models. Oxygen vacancies were found to exhibit a particularly exothermic segregation energy of up to -1.66 eV while protons exhibited segregation energies in the range of -0.47 eV to -0.93 eV. The grain boundary was determined to be predominated by protons below 800 K in 3% H2O and the corresponding space-charge potential was 0.4-0.7 V under the Mott-Schottky approximation. The role of electronic defects in the space-charge properties was evaluated, and it was substantiated that electron conduction along the grain boundary could become evident under reducing conditions.