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Oxygen pressure dependence, electronic

Because Dqq oc [V(5o]then if one measured the radio tracer diffusion of cobalt in CoO, the isothermal oxygen pressure dependence should exhibit a one-quarter dependence. This is exactly what Carter and Richardson ( ) did. Their results are shown in Figure 5. The electronic conductivity, o,... [Pg.82]

All authors cited above established pH and oxygen pressure dependences for the open-circuit potentials in accord with the Nernst formula. This provided good evidence that the experimentally obtained potentials corresponded to the reversible potentials for the four-electron reaction. [Pg.307]

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). [Pg.82]

The oxygen pressure dependence of the concentration of electron holes and the total concentration of the charged metal vacancies (deviation from stoichiometry) correspondingly changes from pg to Pq with increasing deviation from stoichiometry. [Pg.73]

Corresponding expressions for Cei for nonstoichiometric electronic semiconductors readily follows by considering the temperature and oxygen pressure dependence of the concentration of the electronic defects. [Pg.156]

Oxides play many roles in modem electronic technology from insulators which can be used as capacitors, such as the perovskite BaTiOs, to the superconductors, of which the prototype was also a perovskite, Lao.sSro CutT A, where the value of x is a function of the temperature cycle and oxygen pressure which were used in the preparation of the material. Clearly the chemical difference between these two materials is that the capacitor production does not require oxygen partial pressure control as is the case in the superconductor. Intermediate between these extremes of electrical conduction are many semiconducting materials which are used as magnetic ferrites or fuel cell electrodes. The electrical properties of the semiconductors depend on the presence of transition metal ions which can be in two valence states, and the conduction mechanism involves the transfer of electrons or positive holes from one ion to another of the same species. The production problem associated with this behaviour arises from the fact that the relative concentration of each valence state depends on both the temperature and the oxygen partial pressure of the atmosphere. [Pg.236]

Iron(III)-catalyzed autoxidation of ascorbic acid has received considerably less attention than the comparable reactions with copper species. Anaerobic studies confirmed that Fe(III) can easily oxidize ascorbic acid to dehydroascorbic acid. Xu and Jordan reported two-stage kinetics for this system in the presence of an excess of the metal ion, and suggested the fast formation of iron(III) ascorbate complexes which undergo reversible electron transfer steps (21). However, Bansch and coworkers did not find spectral evidence for the formation of ascorbate complexes in excess ascorbic acid (22). On the basis of a combined pH, temperature and pressure dependence study these authors confirmed that the oxidation by Fe(H20)g+ proceeds via an outer-sphere mechanism, while the reaction with Fe(H20)50H2+ is substitution-controlled and follows an inner-sphere electron transfer path. To some extent, these results may contradict with the model proposed by Taqui Khan and Martell (6), because the oxidation by the metal ion may take place before the ternary oxygen complex is actually formed in Eq. (17). [Pg.408]

FIGURE 1.39 Oxygen partial pressure dependency of (a) total conductivity and (b) electronic conductivity of Sm0 2Ce0 8O19 [160]. [Pg.50]

In this case, the number of zinc ions in interstitial positions and the number of free electrons will be decreased by an increase in the partial pressure of oxygen. These disorder reactions result in a dependence of the electrical conductivity on the oxygen pressure. This effect is a well known phenomenon in the field of semiconductors (1). Complicated relations, however, will occur at lower temperatures, at which no equilibrium can be attained between the gas phase and the lattice defects in the whole... [Pg.217]

G. C. Tabisz. Pressure dependence of the electronic transition <— 3Eg in the absoption spectrum of compressed oxygen. Chem. Phys. Lett., 9 581, 1971. [Pg.426]

The reaction was reinvestigated by Cvetanovic (21) who found that within a small analytical uncertainty the exclusive primary step was reaction (11). Formation in this reaction of oxygen atoms in their triplet ground state (OIP) is required by the spin conservation rule and there is now ample chemical evidence that this is indeed so. A primary formar tion of an electronically excited N20 molecule, ruled out in the early work on spectroscopic grounds, is also incompatible with the lack of a pressure dependence of the rate of decomposition. [Pg.121]

The fact that the two n-type oxides Fe203 and ZnO and the two p-type oxides NiO and Cr203 fall into separate classes when the speed and pressure-dependence of their interaction with oxygen is concerned, adsorption of the gas being more difficult and much less in extent on the n-type oxides, is in accord with the view, supported by semiconductivity evidence, that the chemisorption step involves the transfer of electrons from solid to adsorbate. [Pg.214]


See other pages where Oxygen pressure dependence, electronic is mentioned: [Pg.359]    [Pg.216]    [Pg.306]    [Pg.184]    [Pg.630]    [Pg.632]    [Pg.126]    [Pg.165]    [Pg.2266]    [Pg.2268]    [Pg.991]    [Pg.130]    [Pg.136]    [Pg.136]    [Pg.195]    [Pg.236]    [Pg.337]    [Pg.29]    [Pg.150]    [Pg.871]    [Pg.26]    [Pg.316]    [Pg.5]    [Pg.329]    [Pg.9]    [Pg.447]    [Pg.53]    [Pg.56]    [Pg.238]    [Pg.46]    [Pg.46]    [Pg.401]    [Pg.154]    [Pg.1]    [Pg.123]    [Pg.535]   


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