Local environment of Barium, Cerium and Yttrium in BaCe1-xYxO3-δ ceramic protonic conductors

Y-doped barium cerate protonic conductors with composition BaCe1-xYxO3-delta (x=0.02, 0.1, 0.2, 0.3) have been synthesized by sol-gel route, giving by X-ray diffraction tests a homogeneous crystalline phase. A commercial sample BaCe0.8Y0.2O3-delta produced by combustion spray pyrolysis was also provided for comparison aim. The local structure around the cations was studied by X-ray absorption spectroscopy at the K-edges of Ba, Ce and Y. It is demonstrated that the insertion of yttrium in the site of cerium produces a remarkable local distortion of the dopant first-shell octahedral environment that affects also the next coordination shells by a static disorder increasing with dopant amount. For a dopant concentration estimated as x > 0. 17, a poorly crystallized yttrium oxide phase that cannot be detected by X-ray diffraction is segregated. The static disorder around Y noticeably increases in the protonated samples and can be related to a preferential location of protons near the dopant. (C) 2007 Elsevier B.V. All rights reserved.