Solid oxide fuel cells (SOFCs) are one of the most efficient energy conversion devices, yet their high operating temperatures have caused a bottleneck towards their commercialization. Due to sufficient conductivity and stability below 600 °C, doped ceria is under investigation for electrolytic applications in SOFCs. During this study, starting with Ce0.8Sm0.2O2-δ, 5% of Sm3+ was replaced by dopants of varying valencies and sizes giving Ce0.8Sm0.15X0.05O2-δ (where X = Bi3+, Mg2+, Li+), thereby aiming to keep the total dopant concentration constant. The structure-property relationship was studied using a number of techniques including XRD, Raman spectroscopy, FTIR spectroscopy and temperature dependent EIS. XRD indicated the presence of a minor phase belonging to MgO for the Mg2+ co-doped sample. Raman spectroscopy showed the presence of δ-Bi2O3 for Bi3+ doped SDC. Based on the quantitative analysis of Raman data we concluded that the materials were multi-phasic and co-dopants addition did not have a noticeable influence especially on defect concentration. In EIS data, measured from of 550–750 °C, change in conductance behavior was shown by Arrhenius plots for SCB and SCM when the test temperature was raised over 650 °C, possibly reflecting the combined conduction due to the additional phases along with SDC for these samples. Poor solubility of the non-rare earth metal ions into the ceria lattice was observed. This study suggests the need of a comprehensive analysis of doping mechanism preferably by synchrotron-based techniques to effectively incorporate low-cost non-rare earth metals into ceria lattice.