Solid electrolytes oxygen ionic conductivity

Fig. 3. Oxygen transport in solids. 02 is dissociated and ionized at the reduction interface to give O2 ions, which are transferred across the solid to the oxidation interface, at which they lose the electrons to return back to 02 molecules that are released to the stream, (a) In the solid electrolyte cell based on a classical solid electrolyte, the ionic oxygen transport requires electrodes and external circuitry to transfer the electrons from the oxidation interface to the reduction interface (b) in the mixed conducting oxide membrane, the ionic oxygen transport does not require electrodes and external circuitry to transfer the electrons to the reduction interface from the oxidation interface, because the mixed conductor oxide provides high conductivities for both oxygen ions and electrons.

FIGURE 1.1 Oxygen ionic conductivity of various solid-state electrolytes. (Data from Kharton, V.V. et al., Solid State Ionics, 174, 135, 2004.)... 

A solid electrolyte is a material in which the electrolytic, or ionic, conductivity is much greater than the electronic conductivity (for solid electrolytes to be practically useful the ratio of electrolytic to electronic conductivities should be of the order of 100 or greater1,2). Solid electrolytes with conduction ions of 02 , H+, Li+, Na+, Ag+, F, Cl- have all been reported. Much attention has been devoted to oxygen-ion conducting solid electrolytes, many of which show appreciable oxygen-ion conductivities in the range of 200-1200°C. 

Over a large range partial pressures of oxygen ionic conductivity dominates and the material behaves as a solid electrolyte. Under these conditions there is an equilibrium established between oxygen ion vacancies, interstitial oxygen ions and lattice oxygen. 

BIMEVOX — Figure. Oxygen ionic conductivity of solid oxide electrolytes at atmospheric oxygen pressure. See Ref. [ii] for details... 

Figure 9.4 Total conductivity of stabilized zirconia (a) and doped ceria (b) solid electrolytes [34—40], compared to the oxygen ionic conductivity of pyrochlore-type Cd2Zr2O7 5 [41], (Cd,Ca)2Ti2O7 5 [42], (Cd,Ca)2Sn2O7 s [43], and 241707 a [44].

Based on the Wagner method [16], the required character of conductivity can be achieved by the introduction of admixture into the basis oxide, which has a common anion with the basis oxide, and the cation has less valence. Type and quantity of the defects are stipulated by the admixture and its concentration. As a rule, the majority of well-known solid electrolytes with pure oxygen-ionic conductivity have a fluorite CaFj crystalUne structure [17]. 

FIGURE 1.13 1 Low boundary of the oxygen-ionic conductivity for the solid (Zr02)o.9(Y203)o 1 electrolyte and 2 and the temperature dependence of logarithm pressure of dissociation for oxide Na20. (From Zhuiykov, S., Electron model of solid oxygen-ionic electrolytes used in gas sensors, Int. J. Applied Ceramic Techn. 3 (2006) 401-411. With permission.)... 

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