Partial conductivities, dependence

Now we know that such model is very simplified, because these resistors are non-linear and the partial conductivities depend on the applied current [7]. However, even this simplified model turned to be very useful—first of all, for the development of electrolytic processes for production of metals from chalcogenide (mainly poly sulphide) ores. Evidently, for the successful electrowinning of such metals as Sb, Tl, In, Cu, Ag and others from its sulphide, selenide or telluride compounds, the electronic (both semiconductor and metallic) conductivity must be suppressed. For that purpose. Prof. Velikanov proposed and realised, together with his numerous scholars, the additions of compounds with pure ionic conductivity, such as sulphides of sodium and potassium. By studying the conductivities in many binary molten systems, he was able to choose the optimal compositions with high... 

J. Xue, and R. Dieckmann. Oxygen partial pressure dependence of the oxygen content of zirconia-based electrolytes in Ionic and Mixed Conducting Ceramics Second International Symposium 94-12, 191-208 (1994) ES Meeting San Francisco, California. 

FIGURE 1.39 Oxygen partial pressure dependency of (a) total conductivity and (b) electronic conductivity of Sm0 2Ce0 8O19 [160]. 

Figure 16. Oxygen partial pressure dependence of the electrical conductivity of doped Ce02. The steep decrease is due to excess electrons, the flat behavior to oxygen vacancies. If we refer to typical oxygen partial pressures in an SOFC, viz. to 10" bar at the cathode and 0.2 bar at the anode, we see that the conductivity changes from ionic into n-type within a high temperature Ce02 based fuel cell. Reprinted from M. Godickemeier and L.J. Gauckler, J. Electrochem. Soc. 145 (1998) 414-421. Copyright 1998 with permission from The Electrochemical Society, Inc.

For intermediate time resolutions (of the order of r ) the bulk capacitor has become impermeable, and the boundary circuit is relevant for the time dependence (second term in Eq. (64)) term 1 is constant, while term 3 is still zero. Finally in the long-time regime, at t rs, the stoichiometric polarization occurs while both bulk and boundary responses constitute the initial voltage jump from U= 0 to 11 = If (/ , + R ) note that both corresponding capacitors are completely impermeable, i.e., terms 1 and 2 are constant. In the steady state (f rs) all the capacitors block, and R + Kon 316 obtained as the stationary resistance value. Obviously time-resolved dc experiments allow the partial conductivities and the capacitances to be measured together with the chemical diffusion coefficient (ts ccl/Cf). The switching-off behavior is analogous. 

In the case of the asymmetrical cell considered, the voltage variation leads to an one-sided extension of the P0 range, and the detailed evaluation of the correct voltage relation contains easily extractable information on partial conductivities. This is obtained as follows If the Pq2 dependence is a power law (cr oc PtN), Eq. (66) directly leads to... 

Figure 43. Temperature dependence of total and partial conductivities of (a) bulk and (b) grain boundary111 in a 0.016 wt% Fe-doped SrTi03 bicrystal at about 2.0 Pa oxygen. The lower electronic and the much lower ionic grain boundary values are due to Mott-Schottky layer (see Part I, Section V).233 Reprinted from X. Guo, J. Fleig and J. Maier, J. Electrochem. Soc., 148 (2001) J50-J53. Copyright 2001 with permission from The Electrochemical Society, Inc.

Assuming that only the doubly charged zinc interstitials (or oxygen vacancies) contribute to the excess electrons leads to the following oxygen partial pressure dependence of the conductivity ... 

In semiconducting oxides such as iron-doped SrTi03 (e.g., SrTio.8Feo.2O3) the conductivity depends thermodynamically on the oxygen partial pressure. In the thermodynamic equilibrium a metal oxide exchanges lattice oxygen Oq with the ambient gas phase. 

Kuo, C.K., Tan, A., Sarkar, P., and Nicholson, P.S., Water partial pressure-dependent conductance and humidity effects on hydronium-p"-Al203 ceramics, Solid State Ionics, 58, 311-314 (1992). 

Khorkunov, B.A., Nafe, H., and Aldinger, F. 2006. Relationship between the ionic and electronic partial conductivities of co-doped LSGM ceramics from oxygen partial pressure dependence of the total conductivity. Journal of Solid State Electrochemistry 10, 479-487. 

Figure 8.12 Oxygen partial pressure dependence ofthe electrical conductivity for 502( /04)3 ( ) and Sc2(MoO4)3 ( ) at 700 C.

As intensive studies on the ECPs have been carried out for almost 30 years, a vast knowledge of the methods of preparation and the physico-chemical properties of these materials has accumulated [5-17]. The electrochemistry ofthe ECPs has been systematically and repeatedly reviewed, covering many different and important topics such as electrosynthesis, the elucidation of mechanisms and kinetics of the doping processes in ECPs, the establishment and utilization of structure-property relationships, as well as a great variety of their applications as novel electrochemical systems, and so forth [18-23]. In this chapter, a classification is proposed for electroactive polymers and ion-insertion inorganic hosts, emphasizing the unique feature of ECPs as mixed electronic-ionic conductors. The analysis of thermodynamic and kinetic properties of ECP electrodes presented here is based on a combined consideration of the potential-dependent differential capacitance of the electrode, chemical diffusion coefficients, and the partial conductivities of related electronic and ionic charge carriers. 

The main principle, determining the apphcation of solid electrolytes in gas sensors, is based on type of conductivity and on stability of the electrophysical properties at alteration parameters of the measuring environment. In one s turn, type (character) of conductivity depends on structural characteristics of the solid electrolyte, working temperature, and measuring partial pressure. 

From Eq. (2.3) and (2.4) it is apparent that protonic and p-type electronic conduction depend respectively, on the H2O partial pressure and O2 partial pressure. 

Tenqaerature emd Partial Pressure Dependences of Peurtial Conductivities... 

In the previous section we saw the key roles played by the various partial conductivities—or equivalently the transference numbers—in mixed conduction theory. They appear prominently in the integrands of the formulas for open circuit emf emd scaling rate. Thus, if they exhibit any dependences on partial pressure Px2 which is equivalent to Px2 these dependences will have very... 

To begin with we note that the crucial thing here is the dependences of the various partial conductivities on temperature and... 

Clearly each mechanism predicts a different dependence of defect concentration on oxygen partial pressure. Since the electrical conductivity depends on the concentration of conduction-band electrons, measurement of electrical conductivity as a function of oxygen partial pressure should serve to define the dependence law and indicate which defect is predominant. Initial experiments of this type carried out between 500 and 700 indicated that the conductivity varied with oxygen partial pressure having exponents between 1/4.5 and 1 /5. This indicates that neither defect mechanism predominates, and the actual structure could involve both singly and doubly charged interstitial cations. ... 

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