Investigation of proton conductivity in Sc and Yb co-doped barium zirconate ceramics

The oxygen deficient BaZr0.85Sc0.15-xYbxO3-delta (x = 0, 0.05, 0.10) ceramics were synthesized via conventional solid state reaction route. The Rietveld analysis of the x-ray diffraction profile proved that all the prepared compositions presents single phase cubic perovskite symmetry and Pm (3) over barm space group. The actual oxygen occupancy of the materials has been derived from the Rietveld study. Thermo-gravimetric study of the pre-hydrated samples revealed a considerable mass loss, indicating more than 90% of the oxygen vacancies have been successfully filled by protonic defects upon hydration. FESEM images of the fractured surfaces of sintered ceramics showed dense microstructures with sub-micron sized grains and well resolved grain boundaries. The Nyquist plots differentiated the bulk, grain boundary and electrode response at lower temperatures (<= 300 degrees C). The bulk conductivity of the Sc and Yb co-doped barium zirconate was higher compared to that of the respective Sc-doped perovskite oxide. The activation energy of bulk conductivity and total conductivity decreased with the increase in Yb content. The total conductivity of (4.01 x 10(-3) Scm(-1)) at 600 degrees C has been achieved for BaZr0.85Sc0.10Yb0.05O3, suggesting the composition suitable for SOFC applications.