Abstract
Evidence for two distinct conduction regimes comes from experimental investigations on co-doped Ce 1− x (Nd 0.74 Tm 0.26 ) x O 2− x /2 (0.1≤ x ≤0.6) system. At low temperature defects mainly associate as 1 V O . . 2 T m C e ' , trimers, which dissociate above 750 K inducing a lower activation energy. An experimental investigation of the crystallographic, Raman and transport properties of the Ce 1− x (Nd 0.74 Tm 0.26 ) x O 2− x /2 (0.1 ≤ x ≤ 0.6) doped ceria system was performed with the aim of setting out correlations between structural features and ionic conductivity of the material. The chosen composition ensures that the average size of the Nd 3+ and Tm 3+ doping ions coincides with the one of Sm 3+ ; even so, the studied system presents larger cell parameters and a wider compositional extent of the CeO 2 -based solid solution than Sm-doped ceria. Moreover, the occurrence of two different activation energies to ionic conduction below and above ~750 K determines the existence of two distinct conduction regimes. The described experimental results agree with the formation below the threshold temperature of 1 V O . . 2 T m C e ' trimers, which promote the incorporation of Nd C e ' isolated defects into the CeO 2 -based solid solution. In the high temperature range the dissociation of trimers induces the appearance of a lower activation energy; the extrapolation of its value at infinite dilution provides a result in good accordance with the expected binding energy of 1 V O . . RE C e ' dimers, pointing at their stability even in the high temperature conduction regime.
Published Version
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