Ce0.8Gd0.2 − yPryO2 − δ (y = 0–0.05) and Ce0.8Gd0.2 − ySmyO2 − δ (y = 0–0.05) SOFC electrolyte materials were prepared using a reverse-strike co-precipitation method. The resulting powders were characterized using X-ray diffraction, Raman spectroscopy and electrochemical methods. XRD confirmed a single fluorite phase for all compositions. Increased Pr and Sm dopant level was found to cause a shift in the peak positions to slightly higher d-spacings with respect to pure CeO2. The experimental lattice parameter was calculated using the peak positions determined from the XRD patterns. Raman spectra, for all dopant levels, showed two distinctive band features, namely a band at ca. 460 cm−1 and a broader, weaker band at ca. 570 cm−1. As the proportion of praseodymia dopant is increased, the oxygen vacancy band shifts to a slightly lower wavenumber and decreases in relative intensity to the F2g band. However, an anomaly occurs at the 1% dopant level; the oxygen vacancy band having a very low relative intensity. The conductivity was determined using AC–impedance spectroscopy, and it was found that for praseodymia, a maximum is observed at y = 0.015, while for samaria the maximum is observed at y = 0.01. It is also observed that the ionic conductivity for the samaria doped samples are lower than those of the praseodymia doped samples.