Intermediate temperature electronic conductivity

The intermediate- and low-temperature materials exhibit both significant oxygen ion and electron conductivity. This means that the oxygen reduction can take place everywhere in the cathode and is not restricted to the TPBs as in the LSM-type cathodes. An option for compensating the relatively low oxygen ion conductivity of LSC and LSCF at operating temperatures around 600 °C is by mixing the material with (doped) ceria [79, 80],... 

The distance between two cluster molecules is 1.3 nm, i.e., between the naked base and apex of gallium atoms of two clusters, whereby two parallel oriented toluene molecules bridge the intermediate space. Although four-point measurements for electrical conductivity in the temperature range 350 K to 2 K have been carried out, the mechanism of electron conductivity cannot be conclusively explained 83 is... 

Owing to the activation energy, at intermediate temperatures the electrolytic domain increases and at e.g., 500°C the electronic conductivity plays only a minor role. In view of the ionic conductivity being still high enough at these temperatures, ceria appears to be an appropriate electrolyte for intermediate temperature fuel cells. Further information on the properties of ceria and its use in SOFCs can be found in Ref.106,120... 

To reiterate At low temperatures, the conductivity is low because of the paucity of mobile carriers — they are all trapped. As the temperature increases, the defects start to ionize and the conductivity increases with an activation energy needed to release the electrons from their traps. At intermediate temperatures, when kT E, most of the impurities will have donated their electrons to the conduction band, and a saturation in the conductivity sets in. With further increases in temperature, however, it is now possible (provided the crystal does not melt beforehand) to excite electrons clear across the band gap, and the conductivity starts increasing again, but this time with a slope that is proportional to E /2k. 

Intermediate temperatures from about 0.3 to 0.5 at which the surface but not the bulk lattice structure can interact reversibly with the gas. In this temperature range adsorption does not change the bulk composition. However, the resulting change in the surface energy levels does cause electrons to be added to the conduction band, or to be removed from the valence band, and this affects the conductivity. 

During the last four decades, many oxide systems have been examined as potential electrolytes for intermediate temperature (IT) SOFC s [1]. An excellent review was presented by Etsell and Flengas in 1970 [2] while more recent conductivity data are summarized by Minh and Takahashi 3]. The electrolyte for IT-SOFC s have to meet the following criteria high ionic conductivity, low electronic conductivity, chemical and physical stability under reducing and oxidizing atmospheres at the operating temperature, ease of preparation and cost. In Fig. 1, the temperature dependence of the conductivity for several oxide ion conductors is shown. As shown in Fig. 1,... 

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