Lithium vacancy concentration

If the two defects on the right-hand side are dilute, an ideal mass action law can be formulated. The defect concentrations can be connected with the nonstoichiometry (8 = i- v i interstitial Lithium concentration v Lithium vacancy concentration), which is proportional to the storage capacity, while the lithium activity (see the... 

Impurity concentrations for LBO have been determined to be 500 ppm by mass. Carrier concentrations of several hundred ppm (atomic) from conductivity measurements are consistent with the lithium vacancy concentration determined from the type and amount of impurity atoms. This result again indicates that the defect structure of a borate is dominated by impurities. The extrinsic control and limited defect chemistry in these materials is not surprising, because the small size of the B atom and its strong interaction with the 0 atoms should limit substitution of other atoms on the B sites. 

The lithium activity was tuned by annealing polycrystalline LiFeP04 in argon atmosphere at elevated temperatures at which Li is driven to leave the sample. Connected with this is an increased concentration of lithium vacancies (Vli) and holes (h ) ... 

Under conditions in which reaction (3) is not reversible, the temperature dependence of the defect concentrations is rather determined by internal interactions, which is in particular the association between lithium vacancies and holes to neutral lithium vacancies... 

An effect which is frequently encountered in oxide catalysts is that of promoters on the activity. An example of this is the small addition of lidrium oxide, Li20 which promotes, or increases, the catalytic activity of dre alkaline earth oxide BaO. Although little is known about the exact role of lithium on the surface structure of BaO, it would seem plausible that this effect is due to the introduction of more oxygen vacancies on the surface. This effect is well known in the chemistry of solid oxides. For example, the addition of lithium oxide to nickel oxide, in which a solid solution is formed, causes an increase in the concentration of dre major point defect which is the Ni + ion. Since the valency of dre cation in dre alkaline earth oxides can only take the value two the incorporation of lithium oxide in solid solution can only lead to oxygen vacaircy formation. Schematic equations for the two processes are... 

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)] ... 

Note that we have a structure with a "built-in crystal defect, a vacancy. Both the lithium and niobium cations are in an octahedral coordination. In fact, the two ions, Li and Nb , have nearly the same radius and occupy octahedral sites with the same Cgy S5mimetry. The lithium deficiency in congruent crystals is accommodated by means of Nb anti-sites and Nb vacancies in a relative concentration that guaranties overall electrical neutrality. Note that many physical properties depend upon stoichiometry, e.g.- Curie temperature, absorption spectra, lattice parameters and photorefractive yield. 

Experiments conducted on heated LrFeP04/FeP04 mixtures of varying concentrations [185, 186] show that solid solutions form from 0 < x < 1 in LiJePOa at elevated temperatures, however. A representative phase diagram is shown in Fig. 2.10. The solubility limits of lithium in heterosite and vacancies in... 

Pensado et al. [2001] Lithium. Cation and anion vacancies, LiH hydride barrier layer, LiOH outer layer Irreversible reactions with kinetic effects, barrier layer and outer layer dissolution Concentrations of cation and anion vacancies and barrier layer thickness First impedance analysis of bilayer structure and of hydride barrier layer. Cathodic reaction included in the model... 

In order to overcome these stability problems a wide-range of alternative dopants have been studied in an effort to reproduce the transport properties of LISICON whilst eliminating the problems of aging. The introduction of trivalent cations into the basic lithium germanate structure can cause an adjustment in the lithium concentration, but in this case it is possible to introduce additional, interstitial, lithium cations or vacancies on the lithium position. Which of these types of doping occurs depends on the nature of the substitution that occurs. This can be most clearly illustrated by looking at the introduction of aluminium cations. These can enter the structure in place of and so introduce an interstitial lithium cation ... 

From these equations it follows that the concentration of cation vacancies of lithium doped Mni should be lower and the concentration of electron holes higher than that in pure manganous sulfide. As the rate-determining step of the overall sulfidation rate is the diffusional transport of cations through cation vacancies, the protective properties of lithium doped Mni scale should be better than those of pure Mni scale. 

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