Substitutional doping

Figure 23.3 shows the X-ray diffraction patterns for the LiNi n2 04 compounds. The samples were identified as a single-phase spinel until x was 0.3. When the X value was 0.5, there were some other peaks that corresponded to NiO (see Fig. 23.3e). It means that the nickel-doped substituted spinel structure cannot form perfectly solid solutions when x is 0.5. It may be very difficult to prepare the nickel-doped substituted spinel by the solid-state reaction. The NiO peak of LiNi n2 04 sample, which was prepared by the conventional method, was always observed and it could be removed through several recalcination processes at the high temperature. The NiO peak appeared slightly when the X value was only 0.5 in our research and this peak was weak. Our preparation method was more effective than the conventional solid-state method used to synthesize homogeneous metal-doped manganese-substituted spinel.

To a considerable extent, the recent interest in diamond is due to the fact that diamond can be doped. Substitutional boron forms an acceptor with an ionization energy of 360 meV [4] and phosphorus a donor with an ionization energy of 600 20 meV [11]. While these values are large compared to dopands in conventional semiconductors, they nevertheless make diamond a promising semiconductor with a considerable potential for power electronics and optoelectronic devices in the deep UV (5.5 eV = X = 225.8 nm). 

Red ceramic pigments are normally based on cadmium sulfoselenide, which being toxic is banned or restricted in its use in many countries. A need exists, therefore, to prepare an environmental friendly red pigment. Praseodymium doped/substituted ceria is known to be a substitute for cadmium sulfoselenide as red ceramic pigments. Conventionally,... 

Polyaniline (PANI) can be formed by electrochemical oxidation of aniline in aqueous acid, or by polymerization of aniline using an aqueous solution of ammonium thiosulfate and hydrochloric acid. This polymer is finding increasing use as a "transparent electrode" in semiconducting devices. To improve processibiHty, a large number of substituted polyanilines have been prepared. The sulfonated form of PANI is water soluble, and can be prepared by treatment of PANI with fuming sulfuric acid (31). A variety of other soluble substituted AJ-alkylsulfonic acid self-doped derivatives have been synthesized that possess moderate conductivity and allow facile preparation of spincoated thin films (32). 

Significant variations in the properties of polypyrrole [30604-81-0] ate controlled by the electrolyte used in the polymerization. Monoanionic, multianionic, and polyelectrolyte dopants have been studied extensively (61—67). Properties can also be controlled by polymerization of substituted pyrrole monomers, with substitution being at either the 3 position (5) (68—71) or on the nitrogen (6) (72—75). An interesting approach has been to substitute the monomer with a group terminated by an ion, which can then act as the dopant in the oxidized form of the polymer forming a so-called self-doped system such as the one shown in (7) (76—80). 

In a sense, a superconductor is an insulator that has been doped (contains random defects in the metal oxide lattice). Some of the defects observed via neutron diffraction experiments include metal site substitutions or vacancies, and oxygen vacancies or interstituals (atomic locations between normal atom positions). Neutron diffraction experiments have been an indispensable tool for probing the presence of vacancies, substitutions, or interstituals because of the approximately equal scattering power of all atoms. 

A second doping method is the substitution of an impurity atom with a different valence state for a carbon atom on the surface of a fullerene molecule. Because of the small carbon-carbon distance in fullerenes (1.44A), the only species that can be expected to substitute for a carbon atom in the cage is boron. There has also been some discussion of the possibility of nitrogen doping, which might be facilitated by the curvature of the fullerene shell. However, substitutional doping has not been widely used in practice [21]. 

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. 

Modifications of the conduction properties of semiconducting carbon nanotubes by B (p-type) and N ( -type) substitutional doping has also been dis-cussed[3l] and, in addition, electronic modifications by filling the capillaries of the tubes have also been proposed[32]. Exohedral doping of the space between nanotubes in a tubule bundle could provide yet an-... 

Next, let us look at modification of CNTs. There are many approaches to modifying the electronic structure of CNTs oxidation [39], doping (intercalation) [69], filling [70] and substitution by hetero elements like boron and nitrogen atoms [71,72]. There have been few studies on the application of these CNTs but it will be interesting to study applications as well as electronic properties. 

Polyacetylene is considered to be the prototypical low band-gap polymer, but its potential uses in device applications have been hampered by its sensitivity to both oxygen and moisture in its pristine and doped states. Poly(thienylene vinylene) 2 has been extensively studied because it shares many of the useful attributes of polyacetylene but shows considerably improved environmental stability. The low band gap of PTV and its derivatives lends itself to potential applications in both its pristine and highly conductive doped state. Furthermore, the vinylene spacers between thiophene units allow substitution on the thiophene ring without disrupting the conjugation along the polymer backbone. 

There have been very few examples of PTV derivatives substituted at the vinylene position. One example poly(2,5-thienylene-1,2-dimethoxy-ethenylene) 102 has been documented by Geise and co-workers and its synthesis is outlined in Scheme 1-32 [133]. Thiophene-2,5-dicarboxaldehyde 99 is polymerized using a benzoin condensation the polyacyloin precursor 100 was treated with base to obtain polydianion 101. Subsequent treatment with dimethyl sulfate affords 102, which is soluble in solvents such as chloroform, methanol, and DMF. The molar mass of the polymer obtained is rather low (M = 1010) and its band gap ( ,.=2.13 eV) is substantially blue-shifted relative to PTV itself. Despite the low effective conjugation, the material is reasonably conductive when doped with l2 (cr=0.4 S cm 1). 

Figure 13. (a) Substituted polypyrrole, (b) self-doped polypyrrole, (c) heteroaromatic polymer showing the monomer unit, (d) composite polypyrrole-polyelectrolyte, and (e) hybrid material. (Polyaniline macroion photo supplied by Gomez-Romero and M. Lira.)... 

The intrinsic ion-exchange properties of p-doped polymers have been used to bind electrocatalytic anions such as porphyrins238 and phthalocy-anines.239 Cation-substituted polymers have been used to bind anions such as [Fe(CN)6]3-/4-,235 oxometallates,240 and porphyrins241 and anion-substituted polymers have been used to bind a variety of cationic species such as [Co(2,2/-bipyridine)3]3+/2+)58 [Ru(NH3)6]3+/ 2+,183 and porphyrins.242... 

Silicon can be doped with small amounts of phosphorus to create a semiconductor used in transistors, (a) Is the alloy interstitial or substitutional Justify your answer, (b) How do you expect the properties of the doped material to differ from those of pure silicon ... 

For the synthesis of quinolines and isoquinolines the classical approaches are the Skraup and the Bischler-Napieralski reactions. The reaction of substituted anilines with different carbonyl compounds in acid medium has been reported to be accelerated under microwave irradiation to give differently substituted quinolines and dihydro quinolines [137]. Although the yields are much better and the conditions are milder than under conventional heating, the acidity of the medium may prevent the preparation of acid-sensitive compounds. Thus, alternative approaches have been investigated. Substituted anilines and alkyl vinyl ketones reacted under microwave irradiation on the surface of sihca gel doped with InCU without solvent [137] to furnish good yields of quinohnes 213 (Scheme 77). 

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