Doping by substitution

Remark.- Doping by substitution with cations of the same valence as that of the basic cation occurs without affecting defect concentrations because the electric neutrality is not affected by the presence of a doping agent. 

Chemical erosion can be suppressed by doping with substitutional elements such as boron. This is demonstrated in Fig. 14 [47] which shows data for undoped pyrolitic graphite and several grades of boron doped graphite. The mechanism responsible for this suppression may include the reduced chemical activity of the boronized material, as demonstrated by the increased oxidation resistance of B doped carbons [48] or the suppressed diffusion caused by the interstitial trapping at boron sites. 

The photo-Kolbe reaction is the decarboxylation of carboxylic acids at tow voltage under irradiation at semiconductor anodes (TiO ), that are partially doped with metals, e.g. platinum [343, 344]. On semiconductor powders the dominant product is a hydrocarbon by substitution of the carboxylate group for hydrogen (Eq. 41), whereas on an n-TiOj single crystal in the oxidation of acetic acid the formation of ethane besides methane could be observed [345, 346]. Dependent on the kind of semiconductor, the adsorbed metal, and the pH of the solution the extent of alkyl coupling versus reduction to the hydrocarbon can be controlled to some extent [346]. The intermediacy of alkyl radicals has been demonstrated by ESR-spectroscopy [347], that of the alkyl anion by deuterium incorporation [344]. With vicinal diacids the mono- or bisdecarboxylation can be controlled by the light flux [348]. Adipic acid yielded butane [349] with levulinic acid the products of decarboxylation, methyl ethyl-... 

Velapoldl et al. (64) used a similar approach but prepared fibers of uniform diameter (5-45 pm) from Inorganic Ion-doped glasses. The fluorescence parameters of these materials can be changed by substituting various Ions, such as Tb , Sm , Eu , Mn, UOj, Cu, and Sn. They show excellent stability under Irradiation using Incident excitation (measurement Imprecision of 1% under continuous Irradiation In the microscope for 24 h) and have a fluorescence flux density proportional to the fiber length. 

Ni-cermet type anodes have been improved by substituting the YSZ by ceria, gadolinium-doped ceria (GDC) and samarium-doped ceria (SDC). Ceria seems to increase the catalytic activity of the cermet for hydrogen oxidation, while SDC and GDC improve the ionic conductivity of the anode. Ni-ceria cermets are considered the main candidate for low-temperature SOFC [74],... 

Carbon nanostructures can be doped by the introduction/interaction of foreign atoms. Different doping categories include (a) exohedral doping or intercalation, (b) endohe-dral doping or encapsulation or (c) in-plane or substitutional doping. 

CNTs can be easily doped by noncovalent means via molecular adsorption, an aspect that has been considerably exploited to develop ultrasensitive field effect transistor sensors [88-91]. However, substitutional doping with B and N to confer p and n character to the CNTs has also been carried out [92]. Such doped systems can be more susceptible to react with donors or acceptors molecules (depending on the doping) allowing the chemically reactivity to increase. 

The hematite platelets show a predominantly metallic effect. Very thin particles with a thickness of 50 to 400 nm display a pale copper gloss, which is indicative of interference. The shade can be varied and the properties of the platelets can be controlled by doping. A1 or Mn are incorporated by substitution of Fe in the hematite lattice, and Si is incorporated interstitially [5.240]. Laminar iron oxide pigments are interesting because of their excellent fastness to light, outdoor exposure and their good mechanical stability. Main applications up to now are automotive lacquers and cosmetics. 

Aside from the question of the precise model by which relaxation times are interpreted there is the more practical problem of isolating that part of the relaxation specifically caused by diffusion. The contributions of exchange processes (see below), spin-rotation interaction (9), and spin diffusion (9) can be identified by temperature dependences different from that which is solely the result of the motionally modulated nuclear dipolar interaction as sketched above, and corrections can be made. The molecular rotation contributions to dipolar relaxation can be removed or corrected for by (a) isotopic substitution methods (19), (b) the fact that rotation is in some cases much faster than diffusion, and its relaxation effects are shifted to much lower temperatures (7, 20), and (c) doping with paramagnetic impurities as outlined above. The last method has been used in almost all cases reported thus far, more by default than by design, because commercial zeolites are thus doped by their method of preparation this... 

Polymethylacetylene can be doped by I2, but not by AsF5. Its conductivity in the doped state 36) is around 10-3 S cm 1. As might be expected, increasing content of mono- and di-substituted acetylenes in copolymers with acetylene gives increasing solubility at the expense of drastic reductions in the conductivity of both doped and undoped polymers. 

Ideally, lanthanide ions occupy site with C3V symmetry when incorporated into the GaN lattice by substituting the Ga3+. However the actual site symmetry is often found lower than C3V due to strain and defects. So far no crystal field analysis has ever been reported for lanthanide-doped III-V QDs, due to the co-existence of multi-sites which complicates the energy level structure and makes crystal field analysis difficult. Site selective spectroscopy is a very useful tool thus proposed to investigate the different crystal field environments of lanthanide ions doped in III-V QDs. 

Doping by group III elements allows for the substitution of Zn and thus, for the creation of one electron per dopant atom. 

The objective of the present study was to analyze the reasons for the deactivation effects observed in solid Wacker-type catalysts for 1-butene oxidation. For this purpose the catalytic behavior and characteristics of Pd-V205 on alumina catalysts, prepared using either a N PdC or a PdS04 salt, were compared with those of alternative catalysts prepared by substituting the V-oxide with Ce02 in order to obtain a better understanding of the role of V-oxide. In addition, the behavior of a Pd-doped V-heteropolyacid also is discussed to further extend the analysis. 

---