Rare doped zirconia

In the case of the rare-earth-doped zirconias, pyrochlore-structured phases are... 

It can be seen from the figure that, over the temperature range from 1000°C to 400 C, the last two electrolytes have a markedly higher conductivity, than yttria-doped zirconia. It can also be seen from the figure that scandia-doped zirconia has a markedly higher conductivity than yttria-doped zirconia, but it is very rarely used on account of its high price. 

Fig. 3. Conductivity of rare-earth doped zirconia as a function of ionic radius. (Reprinted from Adachi 1988 by permission of the publish, Elsevier Science Ltd.)...

Morscher G.N., Chen K.C., Mazdiyasni K.S. Creep resistance of developmental polycrystalline yttrium aluminum garnet fibers. Ceram. Eng. Sci. Proc. 1994 14 181-188 Mosset A., Gautier-Luneau I., Galy J., Strehlow P., Schmidt H. Sol-gel processed BaTiOa structural evolution from the gel to the crystalline powder. J. Non-Cryst. Solids 1988 100 339-344 NaskarM.K., Ganguli D. Rare-earth doped zirconia fibres by sol-gel processing. J. Mato. Sci. 1996 31 6263-6267... 

An alternative approach to reduce the operating temperature is to use new electrolyte materials such as scandium doped zirconia (SeSZ), and rare earth doped ceria (RDC) which have the fluorite type stmeture, or lanthanum gallate based oxides such as (La,Sr)(Ga,Mg)03 (LSGM) with perovskite stmeture, all of which have higher ionic conductivities than YSZ. An 1 kW class SOFC stack with (La,Sr)(Ga,Mg,Co)03 electrolyte was demonstrated by the collaboration of Mitsubishi Materials Corp. and The Kansai Electric Power Co., Inc. in 2001,... 

Ceria affords a number of important applications, such as catalysts in redox reactions (Kaspar et al., 1999, 2000 Trovarelli, 2002), electrode and electrolyte materials in fuel cells, optical films, polishing materials, and gas sensors. In order to improve the performance and/or stability of ceria materials, the doped materials, solid solutions and composites based on ceria are fabricated. For example, the ceria-zirconia solid solution is used in the three way catalyst, rare earth (such as Sm, Gd, or Y) doped ceria is used in solid state fuel cells, and ceria-noble metal or ceria-metal oxide composite catalysts are used for water-gas-shift (WGS) reaction and selective CO oxidation. 

Moderate doping with rare earth cations such as or 80 + stabilizes cubic zirconia at relatively low temperatures and increases conductivity, the maximum of this quantity being reached when the concentration of acceptor-type dopants is close to the minimum necessary for stabilizing the cubic phase (Kharton et al., 2004). For YSZ,... 

The most commonly used electrolyte materials in SOFCs are based on zirconia and ceria doped with a suitable cation, normally a rare earth (see Chapter 9). The properties that make these two materials attractive for use in fuel cells are discussed in Section 4.4.4, and it is sufficient to note that the most important feature is that they are good oxygen ion conductors. We will focus here on some recent investigations of these materials, with emphasis placed on their methods of preparation. 

Ceria Ceria (CeO2) is similar to zirconia and, in pure form, has the fluorite structure (see Chapters 2 and 9). The dominant point defects are anion Frenkel pairs and, like zirconia, ceria can be doped with rare earth cations to increase the concentration of anion vacancies and increase the oxygen ion conductivity. There is considerable interest in the application of ceria in SOFCs, as it has a higher conductivity than zirconia and can therefore operate at lower temperatures [127]. Unlike zirconia, ceria is readily reduced at elevated temperatures, resulting in the loss... 

Cubic zirconia doped with oxides such as Y203 or CaO is the material of choice for many high temperature applications because of its extremely high ionic conductivity at intermediate and high temperatures. A review on the properties of these specialized rare-earth stabilized zirconia materials has been prepared by Comins et al. [50]. 

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