Doping oxidative

Iodine has proven to be a very effective dopant for polyacetylene. Conductivities as high as 10 S cm have been achieved [14]. Bromine, IBr and ICl also dope polyacetylene [119], but somewhat less effective 

In the early studies of iodine doping, isotropic samples prepared by the Shirakawa method or similar routes were often used [81,120,122,124,125,126,127]. Although the features were there, the lack of orientation severely impeded the interpretation of diffraction patterns. Modelling was partly based on analogies with other intercalation complexes. 

The problem with this model is the major rearrangement of polyaeetylene ehains that is neeessary to turn the P layers into F layers. An alternative has been proposed by Winokur et al. [132]. The aspeet of staging, i.e. the stepwise formation of ordered phases, is 

The existence of I5 anions in heavily doped, well-oriented samples has been questioned at times, when very similar data are interpreted by different investigators [74,134]. From a study of the temperature dependence of the diffraction and the effects of aging, Albouy el a/. [121] have concluded that the scattering of well equilibrated samples can be described on the basis of I3 anions only. Aging involves the release of I2 under ambient conditions, a process which can be enhanced by dynamic evacuation (pumping) and which also proceeds much more rapidly under irradiation. Thermal expansion in relation to conductivity has been explored by Halim et al. [135]. 

Recent diffraction data for highly oriented Tsuka-inoto polyacetylene [22,136] suggest stronger correlations between neighbouring polyiodide columns in this new, highly conductive (cr 10 S cm ) material. Tsukamoto and Takahashi [136] report a monoclinic structure with a = 7.81 A, 6 = 15.62 A, c = 51.2 A and ) = 120 for their fully-iodine-doped polyacetylene. 

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Within the periodic Hartree-Fock approach it is possible to incorporate many of the variants that we have discussed, such as LFHF or RHF. Density functional theory can also be used. I his makes it possible to compare the results obtained from these variants. Whilst density functional theory is more widely used for solid-state applications, there are certain types of problem that are currently more amenable to the Hartree-Fock method. Of particular ii. Icvance here are systems containing unpaired electrons, two recent examples being the clci tronic and magnetic properties of nickel oxide and alkaline earth oxides doped with alkali metal ions (Li in CaO) [Dovesi et al. 2000]. 

There are several approaches to the preparation of multicomponent materials, and the method utilized depends largely on the nature of the conductor used. In the case of polyacetylene blends, in situ polymerization of acetylene into a polymeric matrix has been a successful technique. A film of the matrix polymer is initially swelled in a solution of a typical Ziegler-Natta type initiator and, after washing, the impregnated swollen matrix is exposed to acetylene gas. Polymerization occurs as acetylene diffuses into the membrane. The composite material is then oxidatively doped to form a conductor. Low density polyethylene (136,137) and polybutadiene (138) have both been used in this manner. 

On the contrary such active particles as hydrogen atoms and metals (electron donors), touching the surface of oxides dopes them increasing the surface concentration of electron donors which results in increase in adsorbent conductivity. 

Ranjit KT, Willner I, Bossmann SH, Braun AM (2001) Lanthanide oxide doped titanium dioxide photocatalysts Novel photocatalysts for the enhanced degradation of p-chlorophe-noxyacetic acid. Environ Sci Technol 35 1544—1549... 

Supplit, R Husing, N. Gross, S. Bernstorff, S. Puchberger, M. 2007. Hafnium oxide doped mesostructured silica films. Eur. J. Inorg. Chem. 2797-2802. 

Figure 29 raises the question of how the energies of these two excited states evolve as one goes to longer polyene chains, in analogy to those found in polyacetylenes which become conductive upon oxidative doping (= ionization) or photoexcitation. 

Despite the many investigations of the defect chemistry of lithium-oxide-doped nickel oxide, the real nature of the defect structure still remains uncertain. For many years the holes were regarded as being localized on Ni2+ ions to form Ni3+, written Mi - ... 

Acceptor doping, as in lithium oxide doping of nickel oxide, produces p-type thermistors. The situation in nickel-oxide-doped Mn304 is similar but slightly more complex. This oxide has a distorted spinel structure (Supplementary Material SI), with Mn2+ occupying tetrahedral sites and Mn3+ occupying octahedral sites in the crystal, to give a formula Mn2+[Mn3+]204, where the square parentheses enclose the ions in octahedral sites. The dopant Ni2+ ions preferentially occupy... 

Acceptor doping, as in lithium oxide doping of nickel oxide, leads to the production of holes and produces p-typc thermistors ... 

Later, in Chapter 8 (Section 8.1.2), we will look at in situ spectroelec-trochemistry - the simultaneous monitoring of electrochemical processes with UV-visible spectroscopy. One of the best electrodes for this purpose is a thin film ofln(w) oxide doped with Sn(iv) oxide. Although this mixture of oxides has a relatively good electronic conductivity a, the magnitude of o is never high. 

Indium oxide doped with tin oxide (indium-tin oxide (ITO)) or fluoride-doped tin oxide (often expressed as SnOaiF) are the two favoured layers of choice for most electrochemists and analysts. The thickness of such oxide layers is typically 0.3-0.6 pm, so the ITO-coated side of the electrode displays a pleasant purple sheen . 

Ranjit, K.T., Cohen, H., Willner, I., Bossmann, S., Braun, A. 1999. Lanthanide oxide-doped titanium dioxide effective photocatalysts for the degradation of organic pollutants. J Mater Sci 34 5273-5280. 

Haneda, M Kintaichi, Y Hamada, H. Enhanced activity of metal oxide-doped Ga203-AI2O3 for NO reduction by propene, Catal. Today, 1999, Volume 54, Issue 4, 391-400. 

F NMR of Fluorine-Doped -Alumina. The samples studied 115) were high surface area aluminum oxides doped with fluorine by addition of aqueous HF to alumina and subsequent dehydration. A suflScient number of paramagnetic impurities were present in the samples to give relaxation times of the order of 0.01 second. The BET surface areas of most of the samples examined were within 20% of 250 meterVgram. 

A.l. Alkaline Earth Metal Oxides Doped with Alkali Metals by Chemical Vapor Deposition... 

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