Characterization of the interface between (U, M)O_2±x and yttria-zirconia

Abstract

Solid-state electrochemical cells have been prepared by co-sintering pre-reacted electrode and electrolyte materials together. The electrodes investigated were the non-stoichiometric oxides of the general formula (U, M)O_2±x (M = Sc, Y) and the electrolyte used was yttria-stabilized zirconia. The specimens were characterized by X-ray diffraction, Rutherford back-scattering spectrometry, scanning electron microscopy with energy-dispersive analysis by X-rays, and optical microscopy. For M = Sc, an intermediate phase is formed at the interface and is responsible for the strong bonding of the electrode layer to the electrolyte. The thickness of the intermediate layer was about 2 to 3Μm. Considerable loss of uranium, which in some cases led to destabilization of the fluorite phase, was observed from the surface of the uraniascandia electrode layers. The intermediate phase is thought to be formed as a result of reaction between the electrolyte and volatile uranium-containing species produced by decomposition of the urania-scandia electrode material. For M = Y, no evidence for the formation of such a phase was found and the adhesion of the electrode to electrolyte was poor.