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 compo-sition 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 1VO2Tm\'Ce trimers,which promote the incorporation of Nd\'Ce isolated defects into the CeO2-based solid solution.In the high temperature range the dissociation of trimers induces the appearance of a lower acti-vation energy;the extrapolation of its value at infinite dilution provides a result in good accordance with the expected binding energy of 1VORE\'Ce dimers,pointing at their stability even in the high temperature conduction regime.