Defect structure analysis of proton-oxide ion mixed conductor BaCe0.9Nd0.1O3 − δ

The defect chemical relationship in Nd doped BaCeO3 was discussed based on the defect concentration determined by thermogravimetry and electrical conductivity measured by D.C. 4-terminal method as a function of oxygen partial pressure, P(O2), water vapor partial pressure, P(H2O), and temperature. In BaCe0.9Nd0.1O3 − δ, the defect concentration strongly depended on P(O2), P(H2O) and temperature. This is different from the results of other acceptor-doped BaCeO3 such as BaCe0.9 M0.1O3 − δ (M = Y and Yb), which the concentration of protonic defects is independent of P(O2). The electrical conductivity of BaCe0.9Nd0.1O3 − δ, showed unique P(O2) dependence at high P(O2) atmospheres compared to other acceptor-doped BaCeO3. At temperature above 973 K, σ increased with increasing P(O2). However, at temperature below 873 K, σ decreased with increasing P(O2). This is also different from the general conductivity scheme in other acceptor-doped BaCeO3 that the σ values increase with increasing P(O2) in high P(O2) atmospheres. A different behavior of Nd doped BaCeO3 was explained by considering the changes of oxygen vacancy concentration accompanied by the valence changes of Nd ions between trivalent and tetravalent states.