Conductivity partial pressure dependence

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.

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 ... 

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.

Tenqaerature emd Partial Pressure Dependences of Peurtial Conductivities... 

Figure 25. Water vapor partial pressure dependence on the electrolyte conductivity at various temperatures. Conditions as in Fig. 24.

In terms of maximized electronic and minimized ionic conductivity a material is desirable which is—in the entire partial pressure range occurring in fuel cells—characterized by regime I or II (Fig. 3.2.7). LaCrOs doped with several percent of for example, Sr, Mg or Ca, however, lies in the transition region between regimes III and IV [179-181] and hence exhibits an oxygen partial pressure dependent electronic conductivity (Fig. 3.2.11). 

In practically, some deviations of the observed oxygen partial pressure dependence of the electronic conductivity from that expected for intrinsic Schottky defects have been attributed to the presence of additional ions defects. One possibility is that, even in nominally undoped SrTiOs, impurities are present in amounts large enough to establish the point defect concentration. For example, the aluminum doped SrTiOa, AI2O3 would replace Ti02 [7],... 

The oxygen partial pressure dependence of the conductivity will be similarly changed at high oxygen partial pressures, and then the oxygen partial pressure dependence of the hole concentration is given by... 

Thus, the electronic conductivity is calculated using the permeation flux TIq which can be measured by means of a potentiometric determination of oxygen concentration with a solid electrolyte cell. With the temperature and partial pressure dependence ( Defects in Solids), the following expression is yielded ... 

Therefore, the activation energy of quasi-equilibrium conductivity changes as a logarithm of concentration of adsorption particles which, when the linear dependence between Nt and P is available, corresponds to situation observed in experiment [155]. We should note that due to small value m function (1.91) satisfactorily approximates the kinetics oit) A - B n(i + t/t>) observed in experiments [51, 167, 168]. Moreover, substantially high partial pressures of acceptor gas, i.e. at high concentrations of Nt expression (1.81) acquires the shape ait) Oait/toc) it,Nty " when t>toc>. This suggests that for... 

These recent tests were conducted at applied stress levels similar to those that might be experienced by ASME Section Vm, Division 2 vessels. Test exposure times exceeded 50,000 hours depending on applied stress and temperature. The test specimens were from weldments of thick section plates and represented base metal, weld metal, and heat-affected zone. Detrimental effects of hydrogen were found down to the Figure 1 limit of 850°F (454°C) at 2000 pounds per square inch absolute (14 megapascals) and 3000 pounds per square inch absolute (21 megapascals) hydrogen partial pressure. 

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