Pijolat Michele

Preparation, chemical stability, and electrical properties of Ba(Ce1 − xBix)O3 (x= 0.0–0.5)

Solid solutions of the form Ba(Ce1−xBix)O3 (x = 0.0–0.5) have been prepared by a modified Pechini method at 800 °C in air. XRD results indicate that all the samples have orthorhombic symmetry. Ba(Ce1−xBix)O3 shows no reaction with Ce0.9Gd0.1O2, even when sintered at 1100 °C, but totally decomposes when mixed with yttria-stabilized zirconia (8% Y2O3) and sintered at 900 °C in air. Compared to BaCeO3, the chemical stability of bismuth-doped samples was improved in the presence of moisture. Bismuth substitution for cerium increases the total and electron conductivities. The total conductivity for BaCe0.5Bi0.5O3 is 0.1 S cm−1 at 600 °C in air. Under oxidizing atmospheres, all the samples show p-type conducting properties, whereas in wet argon, the samples show both proton and electron conduction below 600 °C. The proton conduction decreased dramatically with increasing Bi content due to the compensation for oxygen vacancies by [BiCe˙] formed in the lattice. Ba(Ce1−xBix)O3 exhibits a small cathodic overpotential, 70 mV at 800 °C in air at a current density of 100 mA cm−2.

Preparation and electrical properties of a pyrochlore-related Ce2Zr2O8−x phase

A pyrochlore-related Ce2Zr2O8−x phase has been prepared in a reduction reoxidation process from Ce0.5Zr0.5O2 powders. Ce2Zr2O8−x, based on a cubic symmetry with a=1.053 nm, decomposes in nitrogen at 800 °C, but remains stable up to 900 °C in air. It shows mixed oxygen ionic and electronic conductivity. The bulk conductivity at 700 °C is 4×10−4 S cm−1 in air and 1×10−2 S cm−1 in nitrogen, and the activation energy is 1.27 eV in air. In nitrogen, the Arrhenius law is not obeyed, and a curved plot was obtained from 400 to 700 °C; then, the conductivity decreased rapidly due to the thermal decomposition of Ce2Zr2O8−x.