The role of defects association in structural and transport properties of the Ce1-(Nd0.74Tm0.26) O2-/2 system

An experimental investigation of the crystallographic, Raman and transport properties of the Ce1−x(Nd0.74Tm0.26)xO2−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 Nd3+ and Tm3+ doping ions coincides with the one of Sm3+; even so, the studied system presents larger cell parameters and a wider compositional extent of the CeO2-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 trimers, which promote the incorporation of isolated defects into the CeO2-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 dimers, pointing at their stability even in the high temperature conduction regime.