Yttrium-doped zirconia

In general Zr02 oxygen sensors consist of a tube-like solid-state Zr02 electrolyte where the electronic conductivity is based on oxygen ion charge carrier transport. The inner and outer surface of the yttrium-doped and stabilized zirconia tube is covered by porous platinum electrodes. 

Oxygen anions travel from the source side through the solid electrolyte to the sink side (anode) under the combination of the influence of an applied dc electric field and an oxygen chemical potential gradient. At the sink side (the anode of the SOFC), the oxygen anions react electrochemically with both zirconium and yttrium reactants from the sink vapor phase to form the desired product, yttria doped zirconia, and release electrons to the metallic anode. Electrons travel through the external electrical circuit back to the source side for further cathodic reaction. 

Potentiometric sensors for oxygen measurement are typically formed by a layer of stabilized zirconia pressed between two porous Pt electrodes, as schematized in Figure 9.1 (Bard et al., 2008 Pasierb and Rekas, 2009). Such electrodes are in contact with the gas sample and a reference gas, respectively. A typical example is constituted by O2 sensors based on yttrium- or scandium-doped zirconias. The... 

Yttria-doped zirconia and gadolinia-doped ceria oxygen ion conductors and strontium yttrium zirconium oxide proton conductors are being investigated as the solid electrolyte. 

Complex FCC oxides of the fluorite type represent oxygen-conduction solid electrolytes (SOE s). They comprise a typical class of materials for the manufacture of sensors of oxygen activity in complex gas mixtures, oxygen pumps, electrolyzers and high-temperature fuel elements. These materials are based on doped oxides of cerium and thorium, zirconium and hafnium, and bismuth oxide. Materials based on zirconium oxide, for example, yttrium stabilized zirconia (YSZ) are the most known and studied among them. This fact is explained both by their processibility and a wide spectrum of practical applications and by the possibility to conduct studies on single crystals, which have the commercial name "fianites" and are used in jewelry. 

Refining of the particle size can be achieved by etching of bulk sample. For example, the nanosize zirconia powder doped with yttrium has been prepared by etching of yttrium containing polycrystalline BaZrOs or NaaZrOs [15]. Preliminary sintered ceramics of BaZrOs or Na2Zr03 doped with yttrium was subjected to hydrothermal treatment to eliminate the undesirable ions of Ba + or Na+ in nitric acid solution or supercritical water. The etching precipitate represents yttrium-stabilized zirconia nanopowder with particle size of 3-15 nm. 

Formation of large doped zirconia spheres for plasma spray application was the primary target of the work of Chatteijee a/. [ 180,161 ]. In their work, zirconyl chloride and yttrium nitrate pentahydrate were used for the preparation of an aqueous sol. This water phase was used in conjunction with 1,1,1 trichloroethane as the oil phase and Span 80 as the emulsifier. Externally gelled spheres were... 

In many cases of utilizing ionic conduction, the concentration Ci of ionic defects is constant, given by a dopant. For instance, ionic conductivity in yttria-doped zirconia is determined by the concentration of oxide ion vacancies, in turn given as charge compensating the yttrium acceptors, 2[vo ] = [Y ]. If the concentration of acceptors is given in mole-fraction, then it is necessary to multiply the resulting mole fraction of vacancies by the formula density or molar density of the compound in order to obtain the volume density required for insertion in Eq. 6.65 ... 

SDZ scandium-doped zirconia (Zr02)i-x(Sc203) c YSZ yttrium-doped (stabilized) zirconia (Zr02)i- c(Y203) t ... 

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... 

Young s modulus of bulk glass gel, 139 yttria-doped zirconia gel, 150 yttrium aluminum garnet. See YAG yttrium silicate, 151... 

As a practical electrolyte, yttria-doped zirconia is used. The yttrium doping contributes considerably to stabilizing high-temperature phases of zirconia with a high ionic conductivity and to obtain an excellent, durable material for surviving thermal shock. In a commercial oxygen sensor, a porous platinum electrode is placed on the zirconia... 

Doping of rare-earth elements into a sulfate electrolyte also contributes appreciably to obtaining a good ionic conductor similar to the case for stabilized zirconia. Doping causes retention of the high-temperature phase for superior ionic conduction. One different feature between stabilized zirconia and the sulfate electrolyte is that the trivalent rare earth substitutes a monovalent cation site in the sulfate electrolyte, while the tetravalent zirconium site is replaced with trivalent yttrium in zirconia. In the sulfate electrolyte, the vacancy produced is not an anion vacancy but a cation vacancy. Their production also enhances the cationic conduction which reflects in the improvement of the sensing characteristics. 

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