Oxygen nonstoichiometry of the perovskite-type oxides BaCe 0.9M 0.1O 3 − δ (M [dbnd6]Y, Yb, Sm, Tb, and Nd)

Abstract

The oxygen nonstoichiometry, δ, of B-site doped BaCeO 3 − δ under dry condition was determined as a function of oxygen partial pressures, P O 2 , 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 O 2 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 O 2 was well explained by assuming the defect equilibrium 1 2 O 2 + V O • • + 2Nd Ce ' = O O × + 2Nd Ce × .