Conductivity mechanisms and models in anhydrous protonic conductors

Comparison of P(o)) functions obtained for different limiting cases indicates a quasi-continuity existing between a viscous liquid and a solid 

There is also P(to) = toa(to) where a(co) is the frequency dependent conductivity (see Chapter 25). In the case of a low conductivity ionic solid, P(co) is typically of an oscillating behaviour (a peak at = coq, more or less damped, see Fig. 11.2) and there are only very rare diffusive events which contribute to P(co = 0). In a liquid, the spectrum is centred at (u = 0, since all the particles diffuse. When a liquid becomes (more) viscous a pseudo-oscillating behaviour may be observed (c), while the oscillator damping in a superionic conductor may decrease the difference between the time of flight between two sites and the time of oscillation on a site (Fig. 30.2), leading to a quasi-liquid state . In order to simplify the model, either the diffusive or the oscillatory behaviour is assumed to be predominant. The choice may depend on the supposition of relaxation time 

1 Liquid-like models for highly disordered electrolytes 

Glasses and polymer electrolytes are in a certain sense not solid electrolytes but neither are they considered as liquid ones. A glass can be regarded as a supercooled liquid and solvent-free polymer electrolytes are good conductors only above their glass transition temperature (7 ), where the structural disorder is dynamic as well as static. These materials appear macroscopically as solids because of their very high viscosity. A conductivity relation of the Vogel-Tamman-Fulcher (VTF) type is usually 

Diagrammatic representation of diffusion paths observed by numerical simulation (.with permission ) and their correspondence on the conductivity curve ( r(co)) and infrared a sorption (a(co)). Comparison of P(co) functions obtained for an ionic solid (a, Einstein nto el, b, Debye model), a superionic compound (c, dashed line), a viscous liquid (c, solid me) and a Brownian liquid (d).  

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Conductivity mechanisms and models in anhydrous protonic conductors... 

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