Structural and proton conductivity study of BaZr 1- x RE x O 3- δ (RE = Dy, Sm) ceramics for intermediate temperature solid oxide fuel cell electrolyte

Proton-conducting BaZr1-xRExO3-δ (RE = Dy, Sm) (x = 0.05, 0.10, 0.15, 0.20) ceramics were synthesized via a conventional mixed oxide reaction route. The X-ray diffraction patterns indicated that the studied compositions crystallized as a single phase in the cubic space group \( Pm\overline{3}m \). The site preference of the rare earth dopant has been proved by Rietveld analysis of the XRD profile, and the site occupancies have been derived for the studied compositions. Thermogravimetric study of the pre-hydrated samples showed a substantial mass loss, proving the oxygen vacancy filling by H2O after hydration of the samples. Dense microstructures of sintered ceramics are observed, with the Dy-doped compositions showing fairly larger grains (2–3 μm) as compared to Sm-doped barium zirconate. The electrical conductivity under wet N2 (\( {P}_{{\mathrm{H}}_2\mathrm{O}} \) = 0.031 atm) environment has been calculated using electrochemical impedance spectroscopy. The conductivity improved gradually with the increase in doping proportions, in case of both the dopants. However, the conductivity of Dy-doped BaZrO3 is found one order higher as compared to Sm-doped BaZrO3, for any fixed doping concentration. The total conductivity of 20% Dy-doped barium zirconate is found to be 4.15 × 10−3 S/cm at 600 °C which is the highest among the studied compositions. The high proton conductivity suggests the material suitable for solid oxide fuel cell electrolyte at intermediate temperatures.