Synthesis, structure, chemical stability, and electrical properties of Nb-, Zr-, and Nb-codoped BaCeO_3 perovskites

摘要

We report the effect of donor-doped perovskite-type BaCeO_3 on the chemical stability in CO_2 and boiling H_2O 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 BaCe_(1-x)Nb_xO_(3±δ) and BaCe_(0.9-x)Zr_xNb_(0.1)O_(3±δ) (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 BaCe_(1-x)Nb_xO_(3±δ), which is consistent with Shannon's ionic radius trend. Like BaCeO_3, BaCe _(1-x)Nb_xO_(3±δ) was found to be chemically unstable in 50% CO_2 at 700 °C, while Zr doping for Ce improves the structural stability of BaCe_(1-x)Nb_xO _(3±δ). 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 BaCe_(0.9-x)Zr_xNb_(0.1)O_(3±δ) at 400-700 °C, while Zr-free BaCe_(1-x)Nb_xO _(3±δ) exhibits non-Arrhenius behavior at the same temperature range. Among the perovskite-type oxides investigated in the present work, BaCe_(0.8)Zr_(0.1)Nb_(0.1)O _(3±δ) showed the highest bulk electrical conductivity of 1.3 × 10~(-3) S cm~(-1) in wet H2 at 500 °C, which is comparable to CO_2 and H_2O unstable high-temperature Y-doped BaCeO_3 proton conductors.