Bismuth oxide material

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. 

Bismuth Oxides and Bismuthates. The only oxide of bismuth that has been definitely isolated in a pure state is bismuth trioxide. An acidic oxide that approximates the composition Bi20 certainly exists. However, there is considerable question as to the exact nature of this material and the species involved. A number of other oxides have been reported, eg, bismuth oxide (1 1) [1332-64-5], bismuth oxide (1 2), bismuth oxide (2 4)... 

Sardar, K., Playford, H.Y., Darton, R.J., Barney, E.R., Hannon, A.C., Tompsett, D., Fisher, J., Kashtiban, R.J., Sloan, J., Ramos, S., Cibin, G. and Walton, R.I. (2010) Nanocrystalline cerium-bismuth oxides synthesis, structural characterization, and redox properties. Chemistry of Materials, 22 6191-6201. 

Four solid oxide electrolyte systems have been studied in detail and used as oxygen sensors. These are based on the oxides zirconia, thoria, ceria and bismuth oxide. In all of these oxides a high oxide ion conductivity could be obtained by the dissolution of aliovalent cations, accompanied by the introduction of oxide ion vacancies. The addition of CaO or Y2O3 to zirconia not only increases the electrical conductivity, but also stabilizes the fluorite structure, which is unstable with respect to the tetragonal structure at temperatures below 1660 K. The tetragonal structure transforms to the low temperature monoclinic structure below about 1400 K and it is because of this transformation that the pure oxide is mechanically unstable, and usually shatters on cooling. The addition of CaO stabilizes the fluorite structure at all temperatures, and because this removes the mechanical instability the material is described as stabilized zirconia (Figure 7.2). 

Referring to the stack filter, the report of the Court of Inquiry (Penney, 1957) stated Iodine vapour had come through the filter but the major part of the particulate material had been caught by the filter . This was published before analyses of the filter material were available, and was incorrect. Most of the activity on the filter was associated with a yellow powder (Crouch Swainbank, 1958). The powder comprised chain aggregates of submicrometre particles of lead and bismuth oxides, which originated as a fume in the reactor. The distribution of fission products on the powder, as between volatile and refractory elements, was similar to that found in the environment. 

Refs. [i] http /lwww.seca.doe.gov [ii] http //www.spice.or.jp/ fisher/ sofc.html descript [iii] http //www.pg.siemens.com/en/fuelcells/sofc/ tubular/index.cfm [iv] Weissbart J, Ruka R (1962) J Electrochem Soc 109 723 [v] Park S, Vohs JM, Gorte RJ (2000) Nature 404 265 [vi] Liou J, Liou P, Sheu T (1999) Physical properties and crystal chemistry of bismuth oxide solid solution. In Processing and characterization of electrochemical materials and devices. Proc Symp Ceram Trans 109, Indianapolis, pp 3-10 [vii] Singhal SC (2000) MRS Bull 25 16 [viii] Matsuzaki Y, Yasuda I (2001) J Electrochem Soc 148 A126 [ix] Ralph JM, Kilner JA, Steele BCH (1999) Improving Gd-doped ceria electrolytes for low temperature solid oxide fuel cells. In New Materials for batteries and fuel cells. Proc Symp San Francisco, pp 309-314... 

Bismuth oxide forms a number of complex mixed-metal phases with the divalent metal oxides of calcium, strontium, barium, lead, and cadmium, and these show a wide variety in composition. With transition metal oxides, mixed-metal oxide phases have been observed which are based upon a Perovskite-type lattice (10) containing layers of Bi202. It is notable that the high Tc superconducting materials which include bismuth also have this Perovskite-type of lattice with layers of copper oxide interleaved with bismuth oxide layers. 

Azad, A.M., Larose, S., and Akbar, S.A., Bismuth oxide-based solid electrolytes for fuel-cells. Journal of Materials Science, 1994, 29, 4135-4151. 

With the conductivity of an aqueous electrolyte (e.g., IN KCl) serving as a reference, comparable conductivities can be achieved in solid electrolytes under certain conditions. Some of the best solid ionic conductors, commonly referred to as superionic conductors , have resistivities comparable to those of aqueous electrolytes at room temperature (e.g., RbAg4l5 and single crystal MgO-stabilized 6"-alumina). However, they are either in the form of single crystals, which is impractical for most applications, or composed of very expensive and relatively unstable materials. Resistivities comparable to those of aqueous electrolytes can be achieved in solid electrolytes at higher temperatures in both superionic conductors like 6"-alumina (i.e., 300°C) and normal ionic conductors such as stabilized zirconia (800-1000°C), stabilized cerium oxide (>800 C), and stabilized bismuth oxide (>600°C). Sodium ion conducting glasses are much less conductive than polycrystalline 8 -alumina. 

Gryzbowska et al. [106] compared the reaction products formed when pulses of allyl iodide or propene were passed over bismuth oxide or molybdenum oxide. A clear limitation of these experiments is that even the simplest bismuth molybdate catalysts contain neither bismuth oxide nor molybdenum oxide, but instead are made up of a binary oxide of bismuth and molybdenum, whose structure is different to that of bismuth oxide and molybdenum oxide. Gryzbowska et al. selected allyl iodide because of the very low bond dissociation enthalpy associated with the C-I bond, implying that a surface allyl species would readily form from this starting material. In addition, a lower reaction temperature was required for the reaction of allyl iodide than for propene reflecting the greater inherent reactivity of the former. 

As seen from Table 10.1 impressive oxygen fluxes have been reported through 25 mol% yttria-stabilized bismuth oxide (BY25) [110] and 25 mol% erbia-stabilized bismuth oxide (BE25) [111,112], which oxide electrolytes were rendered electronically conductive by dispersion with silver metal. A prerequisite is that both constituent phases in the composite membranes do form a continuous path for both ionic and electronic conduction, having their concentrations above the critical (percolation threshold) volume fraction <])(,. The latter quantity determines the minimum volume fraction in which conduction is possible and is a function of, for example, the relative dimensions and shape of the particles of both constituent phases [113]. In actual composite materials,... 

B. A. Boukamp, K.J. de Vries, A.J. Burggraaf, Surface oxygen exchange in bismuth oxide based materials, in J. Nowotny, W. Weppner (Eds.), Non-Stoichiometric Compounds, Surfaces, Grain Boundaries and Structural Deffcts, Kluwer, Dordrecht, 1989, pp. 299-309. 

Ceramics represent a vast outlet for bismuth compounds, particularly bismuth oxide. Small levels of inclusions have a remarkable impact on the performances of the materials used for electronics. Typical examples of electroceramics are those derived from sintered Bi203-3Sn02, Zn0 Bi203 or 2Bi203-3Ti02. Many of these ceramics can work as sensors for monitoring... 

The (5-phase of bismuth oxide Bi203 is stable between 1002 and 1097 K. This has a fluorite structure so the oxide ions occupy a simple cubic array of sites with only 3/4 occupancy. Alternate cubes are occupied by Bi3 + ions. Generally in the fluorite structure, the vacant cubes favour the formation of anion interstitials, as in CaF2 and SrCl2, but in the (5-phase there are already 25% vacant anion sites, which accounts for its extremely high oxide ion conductivity. MD simulations have been undertaken by Jacobs and MacDonaill (1987) and Jacobs et al. (1990). Radial distribution functions for Bi-Bi and 0-0 obtained from MD simulations of the material are shown in Fig. 4.1. The Bi peaks are sharp and the first four coordination shells are clearly resolved. In contrast, the O peaks are broader with smaller maxima, and the second shell is barely resolved. This is indicative of greater disorder on the oxide sublattice. The FT of g(r) yields the structure factor, but unfortunately experimental data are not available for comparison. (However, for liquid lead there are very detailed and accurate measurements of S(q) at small values of q and a comparison of these measurements to S(q) calculated from an MD simulation at 621 K with N = 21 952 is... 

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