Synthesis, Structure, Chemical Stability, and Electrical Properties of Nb-, Zr-, and Nb-Codoped BaCeO3 Perovskites

We report the effect of donor-doped perovskite-type BaCeO3 on the chemical stability in CO2 and boiling H2O and electrical transport properties in various gas atmospheres that include ambient air, N-2, H-2, and wet and dry H-2. Formation of perovskite-like BaCe1-xNbxO3 +/-delta and BaCe0.9-xZrxNb0.1O3 +/-delta (x = 0.1; 0.2) was confirmed using powder X-ray diffraction (XRD) and electron diffraction (ED). The lattice constant was found to decrease with increasing Nb in BaCe1-xNbxO3 +/-delta, which is consistent with Shannon's ionic radius trend. Like BaCeO3, BaCe1-xNbxO3 +/-delta was found to be chemically unstable in 50% CO2 at 700 degrees C, while Zr doping for Ce improves the structural stability of BaCe1-xNbxO3 +/-delta. AC impedance spectroscopy was used to estimate electrical conductivity, and it was found to vary with the atmospheric conditions and showed mixed ionic and electronic conduction in H-2-containing atmosphere. Arrhenius-like behavior was observed for BaCe0.9-xZrxNb0.1O3 +/-delta at 400-700 degrees C, while Zr-free BaCe1-xNbxO3 +/-delta exhibits non-Arrhenius behavior at the same temperature range. Among the perovskite-type oxides investigated in the present work, BaCe0.8Zr0.1Nb0.1O3 +/-delta showed the highest bulk electrical conductivity of 1.3 x 10(-3) S cm(-1) in wet H-2 at 500 degrees C, which is comparable to CO2 and H2O unstable high temperature Y-doped BaCeO3 proton conductors.