Reorientation mechanism conductivity

The high conductivity of (3-alumina is attributed to the correlated diffusion of pairs of ions in the conduction plane. The sodium excess is accommodated by the displacement of pairs of ions onto mO sites, and these can be considered to be associated defects consisting of pairs of Na+ ions on mO sites plus a V N l on a BR site (Fig. 6.12a and 6.12b). A series of atom jumps will then allow the defect to reorient and diffuse through the crystal (Fig. 6.12c and 6.12d). Calculations suggest that this diffusion mechanism has a low activation energy, which would lead to high Na+ ion conductivity. A similar, but not identical, mechanism can be described for (3"-alumina. 

Molecular reorientations at Bjerrum fault sites are responsible for the dielectric properties of ice. A second type of fault (proton jumps from one molecule to a neighbor) accounts for the electrical conductivity of ice, but cannot account for the high dielectric constant of ice. Further discussion of such ice faults is provided by Franks (1973), Franks and Reid (1973), Onsager and Runnels (1969), and Geil et al. (2005), who note that interstitial migration is a likely self-diffusion mechanism. 

Microwave radiation, as all radiation of an electromagnetic nature, consists of two components, i.e. magnetic and electric field components (Fig. 1.3). The electric field component is responsible for dielectric heating mechanism since it can cause molecular motion either by migration of ionic species (conduction mechanism) or rotation of dipolar species (dipolar polarization mechanism). In a microwave field, the electric field component oscillates very quickly (at 2.45 GHz the field oscillates 4.9 x 109 times per second), and the strong agitation, provided by cyclic reorientation of molecules, can result in an... 

The frequency dependence of NMR SLR time is a powerful method to study the spin dynamics in CPs.107 They reveal the microscopic dynamics of the charge carrier, polaron or conduction electrons. Therefore, interpretation of the NMR relaxation rate is useful, but difficult as other additional mechanisms like the localized paramagnetic centres and molecular motions of reorienting symmetric groups also make considerable contributions to the NMR Tj. 

The type of bonding appears to be more important, that is only single bonds allow rapid reorientation of the bonded proton solvent, which is a persistent element in the proton conduction mechanism. But even for single bonds, significant barriers appear for the rotation of the proton solvent around this bond of the isolated (non-hydrogen bonded) alkane segment, with higher barriers for the phosphonic acid ( 0.10 eV) compared to heterocycles ( 0.04 eV) [101]. 

The mechanism of protonic transport in ZrP is not yet known. Nevertheless, the fact that the conductivity is dominated by surface transport may be explained considering that, due to steric effects, the diffusion and/or reorientation of protonic species on the surface should be easier than in the bulk in addition the ionogenic groups of the surface can be more hydrated than the inner ones, thus facilitating their dissociation and water protonation. 

A new conduction mechanism starts above x 0.35 using HjSQ and H PO (region 11). It corresponds to the appearance of HSQ " or HjPQ " anions. The observed increase of conductivity (Fig. 20.4) is attributed to proton migration along the mixed orH2P04"/HP04 anionic chains by successive proton transfer and anion reorientation steps. 

The earliest ideas about proton conduction in aqueous solutions were stimulated by considerations of the electrolytic decomposition of water in 1806. Grotthuss postulated chains of water dipoles along which electricity may be transported. One basic step which is part of any proton conduction mechanism formulated since the early days of physical chemistry had already been described by several authors at the beginning of this century . They recognized that intermolecular proton transfer can lead to charge transport at a rate exceeding that of other species. The first formal theory was attempted by Huckel in 1928 at a time when the existence of a discrete H30 ion had already been suspected. Huckel treated this species as a dipole and tried to calculate its reorientational rates into positions favourable for proton transfer to neighbouring water molecules. A first quantum mechanical theory of intermolecular proton... 

Quantitative determination of water reorientational and diffusional modes by NMR and 0 tracer experiments on the analogous HUAs provided no correlation with the data for proton conductivity . Instead a good correlation between molecular diffusion and proton conductivity indicated a mechanism in which H2O and HjO are mobile as a whole in the conduction plane without a significant amount of proton transfer between them. The proton conductivity in HUP and HUAs is somewhat higher than that of other monovalent cations in corresponding compounds. This was one of the reasons why molecular diffusion was not... 

Fig. 7. The influence of certain scattering or transport mechanisms on the contributions to thermal conductivity (the symbol is given in the lower right comer of each rectangle) in three temperature regions. 7 n> 7c and T, are the Nccl, Curie and spin reorientation temperatures, respectively.

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