Abstract
In this work, ceria-based ceramics with the composition Gd0.14Pr0.06Ce0.8O2-δ and Sm0.14Pr0.06Ce0.8O2-δ, were synthesized by a simple co-precipitation process using either ammonium carbonate or ammonia solution as a precipitating agent. After the calcination, all of the produced samples were constituted by fluorite-structured ceria only, thus showing that both dopant and co-dopant cations were dissolved in the fluorite lattice. The ceria-based nanopowders were uniaxially compacted and consequently flash-sintered using different electrical cycles (including current-ramps). Different results were obtained as a function of both the adopted precipitating agent and the applied electrical cycle. In particular, highly densified products were obtained using current-ramps instead of “traditional” flash treatments (with the power source switching from voltage to current control at the flash event). Moreover, the powders that were synthesized using ammonia solution exhibited a low tendency to hotspot formation, whereas the materials obtained using carbonates as the precipitating agent were highly inhomogeneous. This points out for the first time the unexpected relevance of the precipitating agent (and of the powder shape/degree of agglomeration) for the flash sintering behavior.
Highlights
One of the main targets of solid oxide fuel cell (SOFC) research regards decreasing their operative temperature to 500–700 ◦ C, towards the future generation of so-called intermediate temperature SOFC.With this in mind, it is necessary to use ceramic electrolytes with both chemical/mechanical stability and adequately high ionic conductivity in said temperature range [1]
flash sintering (FS) was applied to Gd/Pr and Sm/Pr co-doped ceria. Both materials were synthesized via a co-precipitation route using ammonium carbonate or ammonia solution as a precipitating agent, and the relevant effect on the field-assisted sintering process was analyzed in detail
Through the described co-precipitation process in the presence of ammonium carbonate as a precipitating agent, cerium-based co-precipitates are always amorphous in nature, regardless of cerium doping, as clearly stated in our previous works [7,9]
Summary
One of the main targets of solid oxide fuel cell (SOFC) research regards decreasing their operative temperature to 500–700 ◦ C, towards the future generation of so-called intermediate temperature SOFC With this in mind, it is necessary to use ceramic electrolytes with both chemical/mechanical stability and adequately high ionic conductivity in said temperature range [1]. Ceria-based materials generally exhibit poor sinterability, meaning that high temperatures and long timeframes are necessary to achieve adequate densification [8] To overcome this major drawback, many strategies have been proposed. Materials 2019, 12, 1218 or using innovative densification techniques [16,17] Among these methods, flash sintering (FS) has recently been shown to be a very promising consolidation route suitable for densifying ceramics at a reduced temperature via the application of an external electric field [18,19,20]. Both materials were synthesized via a co-precipitation route using ammonium carbonate or ammonia solution as a precipitating agent, and the relevant effect on the field-assisted sintering process was analyzed in detail
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