High oxygen permeability in fluorite-type Ce0.8Pr0.2O2−δ via the use of sintering aids
D.P. Fagg, a, , A.L. Shaulaa, V.V. Khartona and J.R. Fradea
aDepartment of Ceramics and Glass Engineering, CICECO, University of Aveiro, 3810-193 Aveiro, Portugal Received 15 February 2007; revised 21 March 2007; accepted 15 April 2007. Available online 24 April 2007.
Minor (2 mol%) additions of cobalt oxide are highly effective as a sintering additive for the fluorite material Ce0.8Pr0.2O2−δ allowing dense materials to be formed at 1000 °C with sub-micron grain size. The addition gives slightly enhanced total conductivity due to an enhanced electronic conductivity of around two to three times, whilst the level and nature of ionic conductivity is unaffected. This produces a decrease in ionic transference number, an increase in the ambipolar conductivity and importantly a decrease in oxygen surface exchange limitations. The combination of these effects boosts the level of oxygen permeability offered by this fluorite material to levels that can compete with some of the best perovskite oxygen permeation membranes at intermediate temperatures, (<850 °C), in a material that offers good redox stability. As such, the material Ce0.8Pr0.2O2−δ containing minor (2 mol%) additions of cobalt oxide offers one of the highest levels of oxygen permeability reported to date for a single component, mixed conducting, fluorite material.
Keywords: Oxygen permeability; Fluorite; Mixed conductor; Cerium-praseodymiumoxide; Sintering aids