Transport properties in bulk nanocrystalline Sm-doped ceria with doping content between 2 and 30at.%

Fully dense Sm-doped ceria powders, with doping content between 2 and 30 at.% and grain size below 20 nm, were consolidated using a High-Pressure Field Assisted Sintering (HP-FAST) apparatus. Using a uniaxial pressure of 600 MPa relative densities above 95% were achieved at temperatures as low as 600 °C with sintering times of only 5 min. Thanks to these exceptionally mild sintering conditions, grain growth during densification was very limited. The samples were characterized using impedance spectroscopy and the results showed a single semicircle, due to an overwhelming contribution of the grain boundary resistance. Thanks to the brick layer model, the present results were compared to literature data on microcrystalline materials and revealed that, contrary to what previously reported by several authors, negligible modification of the specific grain boundary conductivity can be produced through the reduction of the grain size in Sm-doped ceria in the considered doping interval.