Oxygen nonstoichiometry of the perovskite-type oxides BaCe_0.9M_0.1O_{3 - δ} (M{double bond, short}Y, Yb, Sm, Tb, and Nd)

The oxygen nonstoichiometry, δ, of B-site doped BaCeO_{3 - δ} under dry condition was determined as a function of oxygen partial pressures, P_O2, between 1 bar and 10^{- 4} bar and temperatures between 773 K and 1373 K. The variation of δ in BaCe_0.9Y_0.1O_{3 - δ}, BaCe_0.9Yb_0.1O_{3 - δ}, BaCe_0.9Sm_0.1O_{3 - δ} and BaCe_0.9Tb_0.1O_{3 - δ} was very small through the experimental conditions. This indicates that charge imbalance due to the trivalent dopants is compensated essentially by the oxygen vacancy formation. A large variation was found for δ of BaCe_0.9Nd_0.1O_{3 - δ} by P_O2 and temperature. This result indicates that the valence of the metal elements change under the experimental conditions. The X-ray absorption spectroscopy (XAS) measurement was carried out to examine the valence of the B-site elements of BaCe_0.9Nd_0.1O_{3 - δ}. The samples of different δ were prepared. From the XANES spectra of Ce and Nd, no spectra change for Ce L3-edge was observed, while spectra change was observed for Nd L3-edge and L2-edge. This indicates that the valence of Ce stay unchanged, while the valence of Nd may be changed by the different δ conditions. The measured δ of BaCe_0.9Nd_0.1O_{3 - δ} was analyzed by considering the valence change of neodymium. By considering the defect equilibrium among Nd′_Ce, Nd^×_Ce, V_O^••, and O_O^×, the change of δ against P_O2 was well explained by assuming the defect equilibrium frac(1, 2) O₂ + V_O^{• •} + 2Nd_Ce^' = O_O^× + 2Nd_Ce^×.