The oxygen nonstoichiometry, delta, of B-site doped BaCeO3-delta under dry condition was determined as a function of oxygen partial pressures, Po-2, between 1 bar and 10(-4) bar and temperatures between 773 K and 1373 K. The variation of delta in BaCe0.9Y0.1O3-delta, BaCe0.9Yb0.1O3-delta, BaCe0.9Sm0.1O3-delta and BaCe0.9Tb0.1O3-delta 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 delta of BaCe0.9Nd0.1O3-delta by Po-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 BaCe0.9Nd0.1O3-delta. The samples of different delta 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 delta conditions. The measured delta of BaCe0.9Nd0.1O3-delta was analyzed by considering the valence change of neodymium. By considering the defect equilibrium among Nd'(Ce), Nd-Ce(x), V-O(center dot center dot), and O-O(x), the change of delta against Po-2 was well explained by assuming the defect equilibrium 1/2O(2) + V-O(center dot center dot) + 2Nd'(Ce) = O-O(x) + 2Nd(Ce)(x). (C) 2008 Elsevier B.V. All rights reserved.