Increased ionic conductivity in microwave hydrothermally synthesized rare-earth doped ceria Ce1−xRExO2−(x/2)

Ce0.85RE0.15O1.925 (RE = Gd, Sm), Ce0.8(Gd0.1Sm0.1)O1.9 and CeO2−δ nano-powders were synthesized by microwave-assisted hydrothermal synthesis in a time and energy efficient way. The fluorite-type crystal structure of the synthesized nano-powders was confirmed by X-ray diffraction (XRD) and Rietveld refinement, and the nano-metric particle sizes calculated from the XRD line width broadening were consistent with transmission electron microscopy observations. The Brunauer–Emmett–Teller method was used to confirm large powder surface area. Scanning electron microscopy confirmed high density and low surface porosity of the sintered ceramics as a result of the high sintering activity of the large surface area nano-powders. Impedance spectroscopy was carried out to separately analyze grain boundary (GB) and bulk dielectric relaxations where GB areas were found to constitute ionic charge transport barriers, because their resistance was larger than that of the bulk. Such barriers were found to be comparatively low due to high GB and bulk ceramic ionic conductivities, with the highest values encountered in the composition Ce0.85Sm0.15O1.925. The optimal ionic conductivities encountered were associated with the effect of high sintering activity of the nano-powders.

► Ceria nano-powders synthesis by microwave-assisted hydrothermal synthesis.
► Sintered ceramics show high density and low surface porosity.
► Grain boundaries (GBs) constitute ionic charge transport barriers.
► Highest GB ionic conductivity is encountered in ceramic Ce0.85Sm0.15O1.925.