Tracer surface exchange and diffusion of oxygen in nano crystals of Gd doped CeO2

Abstract

Tracer surface exchange and tracer diffusion of oxygen were investigated in nanocrystals of the ionic conductor CeO2+10%Gd2O3. The use of nano size powders has the advantage that these parameters can be determined on a relatively short time scale even at low temperatures at which their values are low. Two complementary methods were used, a novel one based on SIMS performed on nano powder samples and a residual gas analysis method based on analyzing the composition of the gas-phase (which exchanges tracer material with the powder). The former, SIMS, measurements are novel because of the morphology of the oxide samples, namely powder rather than dense layers or bulk. Isotope surface exchange was found to be the limiting step with diffusion occurring rather rapidly in the small grains used. The values measured for the surface exchange coefficient Ktr are 2.3×10−13 and 9.0×10−13cm/s at 337 and 437°C, respectively for grains of nominally 5nm size. It is found that Ktr increases with increasing grain size.