Yttria stabilized zirconia structure

The parent structure of the anion-deficient fluorite structure phases is the cubic fluorite structure (Fig. 4.7). As in the case of the anion-excess fluorite-related phases, diffraction patterns from typical samples reveals that the defect structure is complex, and the true defect structure is still far from resolved for even the most studied materials. For example, in one of the best known of these, yttria-stabilized zirconia, early studies were interpreted as suggesting that the anions around vacancies were displaced along < 111 > to form local clusters, rather as in the Willis 2 2 2 cluster described in the previous section, Recently, the structure has been described in terms of anion modulation (Section 4.10). In addition, simulations indicate that oxygen vacancies prefer to be located as second nearest neighbors to Y3+ dopant ions, to form triangular clusters (Fig. 4.11). Note that these suggestions are not... 

Figure 25. Proton conductivity of various oxides, as calculated from data on proton concentrations and mobilities, according to Norby and Larring (the type of dopant is not indicated see ref 187 for source data). The conductivity of oxides with a perovskite-type structure are shown by bold lines, and the conductivity of the oxide ion conductor YSZ (yttria-stabilized zirconia) is shown for comparison, (reproduced with the kind permission of Annual Reviews, http //www.AnnualReviews.org).

Mitterdorfer A., Gauckler L.J., 1999. Identification of the reaction mechanism of the Pt, 02(g) yttria-stabilized zirconia system Part I General framework, modelling, and structural investigation. Solid State Ionics 117(3/4), 187-202. 

Yttria-stabilized zirconia f[Zrlj YJ02, /2) is known in the literature as YSZ and has a fluorite-type structure [67] (see Figure 2.16). This material has a high oxygen ion conductivity and is, therefore, applied as a high-temperature electrolyte material, for example, in high-temperature fuel cells [68,73],... 

There is an obvious overlap among various applications categories. An example of the overlap is alumina which is both a structural refractory ceramic as well as a catalyst support. The additives modify the interconversion of various AI2O3 phases and the high surface area of y-Al203 is maintained by the added 3 wt% ceria or lanthana. Additives like yttria stabilize zirconia with respect to inertness and mechanical stability. Addition of yttrium or lanthanide to Fe-Cr-Al alloys reduces the spallation of oxide film. 

Goff, J.P., Hayes, W., Hull, S., Hutchings, M.T., and Clausen, K.N., Defect structure of yttria-stabilized zirconia and its influence on the ionic conductivity at elevated temperatures, Physical Review B, 1999, 59, 14202. 

Other oxygen ion conductors that have potential use as solid electrolytes in electrochemical devices are stabilized bismuth and cerium oxides and oxide compounds with the perovskite and pyrochlore crystal structures. The ionic conductivity and related properties of these compounds in comparison with those of the standard yttria-stabilized zirconia (YSZ) electrolyte are briefly described in this section. Many of the powder preparation and ceramic fabrication techniques described above for zirconia-based electrolytes can be adapted to these alternative conductors and are not discussed further. 

The ion conductivity of bismuth oxide is decreased with increasing concentration of Y2O3 dopant. Dopant concentrations of at least 25 mol% Y2O3 are necessary to stabilize the cubic structure at temperatures below 730°C. The higher conductivity of stabilized bismuth oxide compared to yttria-stabilized zirconia offers the possibility of its use as a solid electrolyte in the solid oxide fuel cell at reduced temperatures. However, the... 

Shimojo, F., Okabe, T., Tachibana, F., Kobayashi, M., Okazaki, H. Molecular-dynamics studies of yttria stabilized zirconia. 1. Structure and oxygen diffusion. J. Phys. Soc. Jpn. 1992, 61, 2848-57. 

Nakamura, A. and Wagner, J.B., Defect structure, ionie conduetivity and diffusion in yttria stabilized zirconia and related oxide eleetrolytes with fluorite structure, J. 

A typical example includes the yttria-stabilized-zirconia-based high-temperature potentiometric oxygen sensor which is widely used in automotive applications. Platinum thick films are applied, forming both the cathode and anode of the sensor. The thick electrode has a porous structure which provides a larger electrode surface area compared to non-porous structures. For current measurement, a porous electrode is desirable since it leads to a larger current output. If the metallic film serves as the electrocatalyst, a porous structure is also desirable, for it provides more catalytic active sites. On the other hand, electrodes formed by the thick-film technique do not have an exact, identical... 

Holland et al. extended the possible oxide structures to include not only silica, mesoporous silica, titania, zirconia, a yttria stabilized zirconia, and alumina but also oxides of W, Fe, V, and Sb [21]. These latter transition metals formed less ordered structures, containing areas of non-porous material. Different dilutions of alkoxide in alcohol resulted in various inorganic loadings, and moderate control in the wall thickness and window sizes between spherical voids [21 ]. SEM images of a series of macroporous titania structures obtained with different alkoxide dilutions in ethanol are shown in Fig. 3. Gundiah and Rao have also prepared macroporous materials of ternary mixed oxides, PdTiOj and Pb(ZrTi)03 [22]. 

Zirconia nanotubes were also obtained using a similar method with a zirconium propoxide precursor [75]. After oxidizing the carbon, zirconia tubes with a diameter of 40 nm, 6 nm wall thickness, and several micrometers long were obtained. The Zr02 was composed of mixed crystal phases (monoclinic and tetragonal). Increased temperature treatment led to collapse of the nanotubes. The addition of yttria in a slightly modified procedure gave a more stable nanotube structure with similar wall thicknesses. The yttria-stabilized zirconia had a cubic structure. 

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