Electronic conductivity, partial

The proportionality constant between the current and the electrochemical potential gradient is controlled by the partial electrical conductivity Jn 

For electronic species (electrons and holes), which may be considered to be sufficiently diluted in an electrolyte, the con- 

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Figure 45. The steady-state voltage of the ion blocking experiment on SrTi03 allows one to determine the partial electronic conductivity. The experiments succeed without encapsulation, simply on the basis of inhibited exchange kinetics (in contrast to Figures 44 and 46).11,239 Reprinted from I. Denk, W. Munch, and J. Maier, J. Am. Ceram. Soc., 78 (1995) 3265-3272. Copyright 1995 with permission from The American Ceramic Society .

W.A. Fisher, Permeation of oxygen and partial electronic conductivities in solid oxide electrolytes, in W. van Gool (Ed.), Fast Ion Transport in Solids. Elsevier, New York, 1973, pp. 503-512.. 

In inorganic melts, the hopping mechanism is caused by the presence of free electrons, which are responsible for the partial electronic conductivity. Free electrons originate in the melt, when cations of the same kind in two oxidation states are present and the electrons jump between the two ions, being in different oxidation states. Such a... 

The next characteristic feature of the metal-metal halide systems is the partial electronic conductivity caused by the presence of the same metallic atoms in two oxidation states. In general, the conductivity of the melt is given by the equation... 

Low values of the parameter pe (ionic transference number, is 0.5) indicate low contributions of partial electronic conductivity to the total conductivity, which result in higher ionic conductivities (k) according to the equation... 

Table 4.2 shows the concentration of chemical impurities in a zirconia single crystal [8]. The concentration of impurities shown here is low and therefore is unlikely to have a significant influence on the ionic conductivity of the zirconia single crystal at low temperatures. The level of impurities concentration shown in Table 4.2 indirectly confirmed that the partial electronic conductivity of the singlecrystal zirconia is negligible. 

When referring to the defect structure in the near-stoichiometry regime, 2[Vd ] w [At] in Figure 10.3c or 10.4b, the ionic conductivity is due to Vo , and essentially is independent of oxygen activity. The variation of the total conductivity in Figure 10.6a and b is, therefore, attributed to that of the partial electronic conductivity,... 

Takahashi, T., Esaka, T., and Iwahara, H. (1977). Conduction in Bi203-based oxide ion conductor under low oxygen pressure. 2. Determination of partial electronic conductivity. J. Appl. Electrochem 7 303-308. 

What is needed are methods to separate the partial ionic and partial electronic conductivities and hence the transport numbers. The transport number, tj[, where i refers to the i species, is defined as the ratio of the current carried by the i species,... 

Equation (5) can be evaluated by analyzing current-voltage plots. The relative contributions of electrons and of holes will vary with material and with the applied potential. Note that increasing values of E tend to increase the current due to electron holes and depress the current due to electrons. In some cases the partial electronic conductivities are so dissimilar that one of the two terms in Eq. (5) may be neglected. For example, CuCl in equilibrium with its parent metal, Cu, conducts electronically via... 

Kim J, Yoo H (2001) Partial electronic conductivity and electrolytic domain of Lao.9Sro.iGao.8Mgo.203-s. Solid State Ion 140(1-2) 105-113... 

In this equation, cr,- is the ionic conductivity, assumed to be independent of Pq2, while Op° and cr ° are parameters describing the other conductivity components at. Po2 of f hn [15]. In Fig. 7b, the ionic transport number cr,7(7,0, is plotted on the same logarithmic scale. In a fuel cell, for example, an H2/O2 ceU, the emf is dependent on the mean ionic transport number. In Fig. 7b, the mean icMiic transport number is the area ratio of the light colored block to the whole block. As a result, partial electronic conductivity limited to the high and low P02 regions is not a problem. This is also observed in practice, where H2/O2 or H2/air cells based on perovskite proton conductors give open circuit voltages within a few percent of the theoretical values [16]. 

While in the experiments described so far both ionic and electronic species are transferred, it is also possible to determine the partial electronic conductivity by using ionically blocking electrodes to suppress the ionic transport so that only electrons and holes can pass. This technique is known as the asymmetric polarization or Hebb-Wagner technique. By using a chemically inert electronic conducting material, no ions will be delivered to the electrolyte when a voltage is applied with such a polarization that the mobile ions tend to be depleted at the inert electrode. An electrode used on the other side fixes the chemical potential of the mobile component of the electrolyte by the applied voltage at that phase boundary. 

Similar to the dc polarization technique for the determination of the partial electronic conductivity in ionic conductors, the electronic majority charge carriers may be blocked by introducing a pure ionic conductor that is permeable to the ions under consideration. In order to provide defined thermodynamic conditions, reversible reference electrodes, which can act as a source or sink for the ions, are employed at the other side of the sample (Figure 9.16). 

Since the concentration of the minor carriers (electrons and/or holes) determines the chemical leakage of oxygen when oxide ion conductor is used as the electrolyte in SOFCs [33], analysis of the performance of electron and hole conduction is an important subject for the electrolyte materials. Partial electronic conduction is commonly analyzed by the ion blocking method, the so-called Wagner polarization method. Partial electronic conductivity is the sum of electronic and hole contribution to the total conductivity, and each conductivity is proportional to a carrier density. Therefore, the total electronic conductivity can be expressed as follows ... 

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