Percolative small-polarons conduction regime in Ce1-xGdxO2-x/2, probed by the EPR spectral intensity of Gd3+

EPR analysis is carried out with Ce1-xGdxO(4-x)/2 (x = 0.1; 0.2) nanopowders aiming at obtaining information about their oxidation and reduction properties. The EPR spectrum of these systems is composed of a single feature. The first derivative peak-to-peak spectral intensity decreases at higher temperatures, but this trend deviates from that of Curie's law with the x = 0.1 sample, at difference with the x = 0.2 sample. This unexpected result is related to oxygen deficiency, due to gas-solid equilibrium, present in the former sample only. As a consequence, some Ce3+ ions would form providing it with conduction electrons propagating as small polarons in a percolative way. This would result in a thinner skin depth at higher temperatures, able to explain the deviation of the spectral intensity from its expected value. Indeed, this deviation from Curie's law is reduced or disappears at all after thermal treatment of the x = 0.1 sample with O-2. (C) 2004 Elsevier Inc. All rights reserved.