In this article we discuss the synthesis of nanoparticles and the preparation of dense nanoceramics of Y-doped CeO 2 . We prepared the nanoparticles by combustion synthesis and characterized the nanopowders by X-ray diffraction, scanning electron microscopy ͑SEM͒, and transmission electron microscopy. The good sintering properties of these nanopowders allowed us to obtain very dense ceramics of Y-doped CeO 2 ͑Ͼ90% theoretical density͒ and keep the grain size small, in some cases around 100 nm, by using sintering temperatures as low as 1250°C and very short annealing times between 5 and 60 min. The microstructure of these nanoceramics was analyzed by atomic force microscopy and SEM. The most interesting feature of these nanoceramics is that the electrical measurements in N 2 ͑p O 2 = 3.5 ϫ 10 −6 atm͒ carried out by the four-point dc technique showed a considerable increase in total conductivity in comparison with the measurements in air or oxygen in the range 700-900°C. This conductivity enhancement might be associated with the electronic contribution to the total conductivity and it is clearly higher than the ionic conductivity in the same temperature range.Ln-doped CeO 2 ͑Ln = lanthanides 3+ or Y 3+ ͒ is a serious candidate for a variety of high-temperature electrochemical devices, such as solid oxide fuel cells ͑SOFCs͒, 1 solid oxide electrolysis cells ͑SOECs͒, oxygen sensors, and oxygen separation membranes, 2 due to its high oxygen ion conductivity. Appropriate aliovalent doping of cerium oxide produces this characteristic high ionic mobility. 3 The most common dopants are Y, Sm, and Gd, but the rest of the lanthanides still need re-evaluation.It is known that high-purity nondoped ceria is an n-type semiconductor. Pure ceria can also show polaronic conductivity in very reducing conditions and at high temperatures after a loss of oxygen. 4 Electronic conduction can also appear when the grain size of nondoped ceria is below 100 nm. 5-8 The presence of electronic or mixed ionic-electronic conduction in reducing atmospheres has also been extensively studied in Ln 3+ -doped CeO 2 repeatedly 9-11 but the electronic conductivity in nanograin-sized doped ceria is not well studied yet.The electrical properties of heavily doped ceria with nanosized grains are still under investigation and just a few reports have been published. 12-15 For example, it has been anticipated that at 500°C the boundary between ionic and electronic regime will be observed at a grain size of 20 nm. 12 There are recent reports that the ionic conductivity of Ce 0.8 Ln 0.2 O 2−␦ ͑Ln = Sm,Y͒ increases with decreasing grain size at temperatures below 200°C 13 and the same seems to be the case for thin films of Gd-doped CeO 2 . 15 There has also been reported a clear dependence of dc conductivity with grain size and doping for Y-doped CeO 2 . 14 Yet the intermediate ͑500-700°C͒ and high-temperature ͑Ͼ700°C͒ behavior of heavily doped nanocrystalline samples in different gas atmospheres is still unknown, despite the fact that doped ceria is a target m...
In this article we discuss the synthesis of nanoparticles and the preparation of dense nanoceramics of Y-doped CeO2. We prepared the nanoparticles by the combustion method and characterised the nanopowders by XRD, SEM and TEM. The good sintering properties of these nanopowders allowed us to obtain very dense ceramics of Y-doped CeO2 and keep the grain size in some cases around 100 nm using sintering temperatures as low as 1250 {degree sign}C and very short times of 5 to 60 min. The microstructure of these nanoceramics was analysed by AFM and SEM. The most interesting feature of these nanoceramics is that the electrical measurements in N2 carried out by the 4-point dc technique showed a considerable increase in conductivity in comparison with the measurements in air or oxygen in the range 700-900 {degree sign}C. This might be associated with electronic conduction.
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