Effects of ZnO additive on the electrical and densification properties of A-site deficient barium cerate perovskite

The dual strategies of A-site deficiency and addition of ZnO sintering aid have been employed to optimise stability and densify the high-temperature proton conductor Ba 0.95 Ce 0.8 Y 0.2 O 3-δ at 1200 °C (B95CYZn-1200). Structural analysis performed by Rietveld refinement based on X-ray diffraction data indicated perovskite phase with monoclinic symmetry (space group, I2/m). Raman spectroscopy revealed the presence of ZnO for material sintered at 1200 °C, which most likely partially resides in grain-boundary regions, leading to enhanced electrical transport observed by impedance spectroscopy at low temperature. Anomalous and reproducible frequency-dependent impedance behaviour below 500 °C, observed in various atmospheres, is suggested to be attributable to the varistor-type properties of ZnO. The electrical conductivity of B95CYZn-1200 in the range 500–900 °C is typical of perovskite proton conductors but with greater conductivity than both Ba-stoichiometric BaCe 0.8 Y 0.2 O 3-δ and ZnO-free Ba 0.95 Ce 0.8 Y 0.2 O 3-δ in wet O 2 and N 2 , reaching ∼ 1.1 S m −1 at 550 °C in wet O 2 . Resistance to carbonate formation and mechanical breakdown was demonstrated via prolonged impedance measurements in CO 2 - and H 2 -containing atmospheres in the range 600–700 °C. • ZnO sintering aid optimises densification of Ba 0.95 Ce 0.8 Y 0.2 O 3-δ at 1200 °C. • High stability of ZnO-added Ba 0.95 Ce 0.8 Y 0.2 O 3-δ in CO 2 and H 2 atmospheres. • Higher conductivity of Ba 0.95 Ce 0.8 Y 0.2 O 3-δ attributable to ZnO. • Grain-boundary ZnO induces varistor action at low temperature.