Proton conducting BaCe0.8Y0.2O2.9−δ (BCY) was prepared by solid-state sintering at various elevated temperatures (1623- 1873 K) to control its microstructure and defect chemistry at the grain boundaries. The bulk and grain boundary conductivity were measured over the temperature range of 373-1173 K under 4% H2/balanced by He (pH2O = 0.03 atm) by an AC impedance analyzer (Solatron 1260). For the ternary BCY system, the predominant configuration of majority defect pairs was described as functions of pO2, aBaO, and temperature and a space charge potential theory was developed. It was shown by TEM that the grain boundaries of the sintered disks were free of any second phase. The depletion of effectively positively charged protons with a positive space charge potential with respect to the bulk (φ∞ = 0) was explained by negatively charged yttrium enrichment across the grain boundaries. The bulk conductivity was around two orders of magnitude higher than the grain boundary conductivity.

Keywords: Proton conductor, BaCe0.8Y0.2O2.9−δ, Space charge potential.