Lithium doping

T. Ito and J. H. Lunsford, Synthesis of ethylene and ethane by partial oxidation of methane over lithium-doped magnesium oxide, Nature, 1985, 314, 721. 

Wang SB, Murata K, Hayakawa T, Hamakawa S, Suzuki K (1999) Excellent performance of lithium doped sulphated zirconia in oxidative dehydrogenation of ethane. Chem Commun 103-104. 

Fig. 27. Differential heats versus coverage for the successive adsorptions, at 30°C, of carbon monoxide (A), oxygen(B), and, again, carbon monoxide (C) on the surface of lithium-doped nickel oxide. Reprinted from (54) with permission J. Chim. Phys.

The analysis of the thermograms recorded during the interaction of the successive doses of the different reactants in the sequence may also yield very relevant informations. Through the use of different techniques, it has been shown, for instance, that the different steps of the mechanism of the CO oxidation, at room temperature, at the surface of pure [TNJiO (200)3 19, 82) or lithium-doped 54) nickel oxide, may be written ... 

As in the previous chapter, most work has been carried out on oxides, and these figure prominently here. As the literature on oxides alone is not only vast but is also rapidly increasing, this chapter focuses upon a number of representative structure types to explain the broad principles upon which the defect chemistry depends. However, despite considerable research, the defect chemistry and physics of doped crystals is still open to considerable uncertainty, and even well-investigated simple oxides such as lithium-doped nickel oxide, Li Nij- O, appear to have more complex defect structures than thought some years ago. 

Kiwi, J., Morrison, C. 1984. Heterogeneous photocatalysis-dynamics of charge-transfer in lithium-doped anatase-based catalyst powders with enhanced water photocleavage under ultraviolet-irradiation. J Phys Chem 88 6146-6152. 

For instance, poly-p-phenylenes in their doped states manifest high electric conductivity (Shacklette et al. 1980). Banerjee et al. (2007) isolated the hexachloroantimonate of 4" -di(tert-butyl)-p-quaterphenyl cation-radical and studied its x-ray crystal structure. In this cation-radical, 0.8 part of spin density falls to the share of the two central phenyl rings, whereas the two terminal phenyl rings bear only 0.2 part of spin density. Consequently, there is some quinoidal stabilization of the cationic charge or polaron, which is responsible for the high conductivity. As it follows from the theoretical consideration by Bredas et al. (1982), the electronic structure of a lithium-doped quaterphenyl anion-radical also differs in a similar quinoidal distortion. With respect to conformational transition, this means less freedom for rotation of the rings in the ion-radicals of quaterphenyl. This effect was also observed for poly-p-phenylene cation-radical (Sun et al. 2007) and anion-radical of quaterphenyl p-quinone whose C—O bonds were screened by o,o-tert-hutyl groups (Nelsen et al. 2007). 

Most mechanistic studies have focused on elucidation of the role of alkali promoters. The addition of Li+ to MgO has been shown to decrease the surface area and to increase both methane conversion and selective C2 production.338,339 As was mentioned, however, besides this surface-catalyzed process, a homogeneous route also exists to the formation of methyl radicals.340-342 The surface active species on lithium-doped catalysts is assumed to be the lithium cation stabilized by an anion vacancy. The methyl radicals are considered to be produced by the interaction of methane with O- of the [Li+0-] center330,343 [Eq. (3.32)]. This is supported by the direct correlations between the concentration of [Li+0 ] and the concentration of CH3 and the methane conversion, respectively. The active sites then are regenerated by dehydration [Eq. (3.33)] and subsequent oxidation with molecular oxygen [Eq. (3.34)] ... 

Figure 4 shows ESR spectra for lithium-doped coronene monoanion in THF solution. There is no significant difference between the lithium-doped sample and the sodium-doped one. Hence, the observed signals are due to the monoanion itself. In Section 5.2, we consider the reason why JT Effect was not observed in this system using ab initio calculation. 

Fig. 4. Temperature dependence of the observed ESR spectra of lithium-doped coronene anion.

A single-layer OLED with [Er(acac)3phen] doped into a 80-nm thick film of PVK (see fig. 117) prepared by spin-coating and deposited on an ITO electrode, and with a 100-nm lithium-doped (0.1%) aluminum cathode has also been tested and shows an onset voltage of about 12 V for electroluminescence (Sun et al., 2000). [Er(dbm)3bath] has a photoluminescence quantum yield of 0.007% in dmso-7fl at 1 mM concentration the OLED based on this compound and similar to the one described above for Ndm has a NIR external electroluminescence efficiency of 1 x 10-6 (Kawamura et al., 2001). 

Although the mechanism of conduction in lithium-doped NiO and other low-mobility semiconductors is a controversial matter, the simple polaron hopping model outlined above serves well as a basis for understanding conduction processes in many of the systems discussed later (eg Section 4.4.1). 

The TCR of a semiconductor is expected to be negative (see Section 2.6) whether the conducting electrons move in a conduction band, as for example in SiC, or hop between localized sites as is believed to occur in lithium-doped NiO (see Section 2.6.2). In each case the resistivity p depends on temperature according to... 

Wang JX, Lunsford JH. Characterization of [Li+O] centers in lithium-doped magnesium oxide catalysts. J Phys Chem. 1986 90 5883-7. 

Lithium-doped polyacetylene. This material would be practical, but the linewidth is of order AHpp 90 mG, which is larger than most requirements. 

Figure 24.9 Effect of lithium doping on the conductivity of P, DCA. The addition of even small amounts (2%) LiDCA results in a dramatic increase in the conductivity of the material.

Figure 24.13 Effect of lithium doping and temperature on the i, F, and diffusion in P13DCA. Doping the material with 2% UBF4 results in a decrease in cation diffusion, it is believed that an increase in salt concentration results in increased ion interaction and thus in a loss of mobility.

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