Conductivity electric, perovskite-type oxides

S. Sekido, H. Tachibana, Y. Yamamura and T. Kambara, Electric-ionic conductivity in perovskite-type oxides, SrxLai-xCoi-yFey03-8- Solid State Ionics, 37 (1990) 253-259. 

Figure 20-23. Dependence of electric conductivity of perovskite-type oxides on the water vapor content in air at 400 °C ...

Fig. 2 shows the temperature as a function of irradiation time of Cu based material under microwave irradiation. CuO reached 792 K, whereas La2Cu04, CuTa20e and Cu-MOR gave only 325, 299 and 312 K, respectively. The performances of the perovskite type oxides were not very significant compared to the expectation from the paper reported by Will et al. [5]. This is probably because we used a single mode microwave oven whereas Will et al. employed multi-mode one. The multi-mode microwave oven is sometimes not very sensitive to sample s physical properties, such as electronic conductivity, crystal sizes. From the results by electric fixmace heating in Fig. 1, at least 400 K is necessary for NH3 removal. So, CuO was employed in the further experiments although other materials still reserve the possibility as active catalysts when we employ a multi-mode microwave oven. 

Yamada H, Nagamoto H (1993) Thermal expansion coefficient and electrical conductivity of Mn-based perovskite-type oxides. In Singhal SC, Iwahara H (eds) Proceedings of the 3rd International symposium on solid oxide fuel cells, vol 93-94. The Electrochem Society Inc. Proceedings, Pennington, pp 213-219... 

For a doped oxide M2O3 exhibiting anti-Frenkel disorder, Colomban and Novak present a sehematie Kroger-Vink diagram of the extrinsic and intrinsic point defects as a function of the partial water pressure. With regard to electrical properties, the proton conductivity in the binary metal oxides is usually much lower than in the perovskite-type oxides. ... 

YSZ fonning La2Zr207. The electrical conductivity of these perovskite type oxides exhibit a metalhc temperature dependence, which indicates that the election is delocalized around transition metal ions. 

The perovskite-type catalysts (ref.l), other non noble metal complex oxides catalysts (ref.2), and mixed metal oxides catalysts (ref.3) have been studied in our laboratory. The various preparation techniques of catalysts (ref.4 and 5), the adsorption and thermal desorption of CO, C2H5 and O2 (ref.6 and 7), the reactivity of lattice oxygen (ref.8), the electric conductance of catalysts (ref.9), the pattern of poisoning by SO2 (ref. 10 and 11), the improvement of crushing strength of support (ref. 12) and determination of the activated surface of complex metal oxides (ref. 13) have also been reported. 

Certain oxides with a perovskite structure are generally applied to the cathode. For high temperature type SOFCs, doped-LaMn03 is used as the typical cathode. For low temperature SOFCs, LaSr(CoFe)03 or La(NiFe)03 are used as the cathode. Doped LaCo03 has a high electric conductivity and shows an excellent catalytic performance. However, the TEC of LaSrCo03 is larger than that of the electrolyte, and so Fe is substituted to reduce the TEC of the cathode. 

Both elements form dioxides, M02, that have distorted rutile structures in which there are M M bonds. Re03 is an important oxide but Tc03 is not known to exist. The structure of red Re03, shown in Fig. 18-D-l, is also adopted by Cr03, W03, and others and is very similar to the perovskite structure. Re03 has metallic type electrical conductivity due to delocalization of the Re 1 electrons in a conduction band of the solid. 

Electrodes The anodes of SOFC consist of Ni cermet, a composite of metallic Ni and YSZ, Ni provides the high electrical conductivity and catalytic activity, zirconia provides the mechanical, thermal, and chemical stability. In addition, it confers to the anode the same expansion coefficient of the electrolyte and renders compatible anode and electrolyte. The electrical conductivity of such anodes is predominantly electronic. Figure 14 shows the three-phase boundary at the interface porous anode YSZ and the reactions which take place. The cathode of the SOFC consists of mixed conductive oxides with perovskite crystalline structure. Sr doped lanthanum manganite is mostly used, it is a good /7-type conductor and can contain noble metals. 

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