Transport Properties of Fluorite-Type Ce0.8Pr0.2O2-delta: Optimization via the Use of Cobalt Oxide Sintering Aid

authors	Fagg, DP; Garcia-Martin, S; Kharton, VV; Frade, JR
nationality	International
journal	CHEMISTRY OF MATERIALS
keywords	CERIA SOLID-SOLUTIONS; OXYGEN PERMEABILITY; THERMAL-EXPANSION; MIXED CONDUCTORS; ELECTRICAL-CONDUCTIVITY; ELECTRONIC TRANSPORT; FUEL-CELLS; O SYSTEM; PR; MICROSTRUCTURE
abstract	Dense Ce0.8Pr0.2O2-delta ceramic membranes with submicron grain size can be formed at 1000 degrees C by minor additions of cobalt oxide. X-ray energy-dispersive spectroscopy shows the additive to be located in the grain boundary. Although a very fine grain interface is obtained for the composition containing 2 mol % cobalt oxide, pronounced grain boundary layers and Co-rich fringes are noted at 5 mol %. The cobalt oxide additions enhance electronic conductivity by around 2-3 times. For 2 mol % additions, no change to the level or nature of ionic conductivity is observed, whereas at 5 mol %, a depleted ionic conductivity is noted at lower temperatures. Coulombic titration studies show the bulk Pr oxidation state to be unaffected by the additions. Jointly, these results prove that the Co additions are not accommodated in the bulk material but instead form additive-rich grain boundary networks that are electronically conductive. Materials essentially free from oxygen surface exchange limitations are produced on addition of 2 mol % cobalt oxide, in contrast to that noted for 5 mol %. The combination of enhanced ambipolar conductivity and enhanced oxygen surface exchange kinetics boosts oxygen permeability in 2 mol % cobalt oxide doped Ce0.8Pr0.2O2-delta to offer one of the highest levels of oxygen permeability reported to date for a single component mixed conducting fluorite material.
publisher	AMER CHEMICAL SOC
issn	0897-4756
year published	2009
volume	21
issue	2
beginning page	381
ending page	391
digital object identifier (doi)	10.1021/cm802708a
web of science category	Chemistry, Physical; Materials Science, Multidisciplinary
subject category	Chemistry; Materials Science
unique article identifier	WOS:000262605200027