Nickel oxide gallium-doped

Figure 13.19 The conversion of insulating oxides into semiconductors, (a) (i) Nickel oxide (NiO) doped with hthium oxide (Li20), making it a p-t)fpe semiconductor, and (ii) the energy-band structure of Li+-doped NiO. (b) (i) Zinc oxide (ZnO) doped with gallium oxide (Ga203), making it an n-type semiconductor, and (ii) the energy-band struemre of Ga -doped ZnO...

Preadsorption of oxygen at 30°C on the surface of a gallium-doped nickel oxide produces, for instance, a considerable increase of the differ-... 

Fig. 25. Differential heats of adsorption of carbon monoxide at 30°C on fresh (A) or oxygenated (B) samples of a gallium-doped nickel oxide. Reprinted from (63) with permission J. Chim. Phys.

Thermochemical Cycles Testing the Formation of Gaseous (Cycle 1) or Adsorbed (Cycle 2) Carbon Dioxide by the Interaction of Carbon Monoxide with Oxygen Preadsorbed on Gallium-Doped Nickel Oxide ... 

Fig. 26. Differential heats of interaction of carbon monoxide at 30°C with a sample of gallium-doped nickel oxide, containing a limited amount (0.4 cm3 02 gm l) of preadsorbed oxygen.

One of the conclusions deduced from the thermochemical cycle 2 in Table V, for instance, is that in the course of the catalytic combustion of carbon monoxide at 30°C, the most reactive surface sites of gallium-doped nickel oxide are inhibited by the reaction product, carbon dioxide. This conclusion ought to be verified directly by the calorimetric study of the reaction. Small doses of the stoichiometric reaction mixture (CO + IO2) were therefore introduced successively in the calorimetric cell of a Calvet microcalorimeter containing a freshly prepared sample of gallium-doped... 

Properties of doped oxides are summarized in Table X. The fraction of added lithium ions which is not extracted from the dehydrated solid by boiling water is considered as dissolved into the lattice of nickel oxide (80). It appears that the maximum solubility of lithium in nickel oxide is 2 at. % Li in these experiments (Table X). Because of the low temperature of firing (250°), lithium ions are most probably located in the surface layers of the oxide lattice. The amount of dissolved gallium ions is not known. 

Surface areas of pure or doped nickel oxides are not very different (Table X). It seems, however, that incorporation of lithium increases slightly the surface area of the solid and that incorporation of gallium ions has the opposite effect. 

Gallium-doped nickel oxide contains more metallic nickel than pure or lithiated nickel oxides (Table X). Concentrations of metal deduced from magnetic susceptibility measurements (23) are, moreover, in agreement with the results of chemical analyses (30). The following mechanism of incorporation explains these results (80) ... 

The calorimetric study of interactions on the surface of gallium-doped nickel oxide therefore yields results which are similar to those obtained on pure Ni0(250°), although the incorporation of trivalent ions changes somewhat the surface affinity toward oxygen. In both cases, two reaction mechanisms for the production of gaseous carbon dioxide are probable. In mechanism II, a reaction intermediate, C03-(ads) is formed whereas, in mechanism I, gaseous carbon dioxide is produced directly by the interaction of carbon monoxide with adsorbed... 

From the calorimetric results of the study of surface interactions, it has been deduced (Section VI, C) that on the surface of the gallium-doped nickel oxide, as in the case of NiO(250°), two reaction paths are probable (mechanisms I and II). The actual reaction mechanism on NiO(10 Ga)(250°) is discriminated, as in the former case (Fig. 24), by... 

Because of the potential importance for industrial-scale catalysis, we decided to check (i) whether an influence of a semiconductor support on a metal catalyst was present also if the metal is not spread as a thin layer on the semiconductor surface but rather exists in form of small particles mixed intimately with a powder of the semiconductor, and (ii) whether a doping effect was present even then. To this end the nitrates of nickel, zinc (zinc oxide is a well-characterized n-type semiconductor) and of the doping element gallium (for increased n-type doping) or lithium (for decreased n-type character) were dissolved in water, mixed, heated to dryness, and decomposed at 250°-300°C. The oxide mixtures were then pelleted and sintered 4 hr at 800° in order to establish the disorder equilibrium of the doped zinc oxide. The ratio Ni/ZnO was 1 8 and the eventual doping amounted to 0.2 at % (75). 

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