Doping from metal vapor phase

The doping level can be controlled electrochemically or by doping from the metal vapor phase. This has been studied extensively for alkali insertion, and the existence of stages has been clearly demonstrated and studied thoroughly [56], as well as the corresponding conductivity changes [59]. 

Semiconductor oxides are also important support materials. Even if a support is inactive in the reaction imder consideration, it can considerably change the reactivity of the catalyst that it supports. As an example, metals such as Ni and Ag are often applied to doped AI2O3 by vapor-phase deposition. The resulting catalyst system behaves like a rectifier in that electrons flow from the support through the catalyst metal to the reac-tauts (Eq. 5-61). Hence in this case acceptor reactions are favored. 

Oxygen anions travel from the source side through the solid electrolyte to the sink side (anode) under the combination of the influence of an applied dc electric field and an oxygen chemical potential gradient. At the sink side (the anode of the SOFC), the oxygen anions react electrochemically with both zirconium and yttrium reactants from the sink vapor phase to form the desired product, yttria doped zirconia, and release electrons to the metallic anode. Electrons travel through the external electrical circuit back to the source side for further cathodic reaction. 

The alkaline earth metal-doped phases Ca5C, 5Qo nd, surprisingly, have been found to be superconducting. In these systems, not only the hu LUMO but also the are involved. In these systems, particularly Ba Cgo, charge transfer from the metal to the fullerene cannot be complete. Calculations show that there is considerable hybridization between alkaline earth metal d levels and the Qo Jt states. Again, photoemission studies have played a major role in following the nature of electron doping. These systems are mOj.g difficult to prepare than the alkali metal systems because of the lower vapor pressures of the metals. The azide route seems to be an effective method for their preparation. 

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