Oxygen transport studies in nanocrystalline ceria films

Abstract

Oxygen uptake and conductivity were measured by nuclear-reaction analysis and alternating current impedance technique at the intermediate temperature range on sol-gel grown nanocrystalline ceria films with average grain-sizes 7 nm and 38 nm synthesized at 723 and 1173 K, respectively. Higher oxygen uptake and lower ionic conductivity were observed in ceria films with ∼7-nm grain size. High permeation-assisted oxygen diffusion in nanocrystallites combined with oxygen trapping in the disordered region contributed to higher oxygen uptake. However, the lower ionic conductivity in the film resulted from the absence of long-range lattice ordering and inactive grain-boundary/surface oxygen vacancy sites due to oxygenation. The relationship between oxygen uptake and conductivity in ceria is discussed in details by considering grain-size dependent defect density, related surface area, and enhanced oxygen mobility.