Glasse ionically conducting

Free volume concept also held much attraction in modeling fast ion conduction in glasses. Ionic conduction is formulated by assuming that the mobile cation, / has its own transition rate v, which depends on its... 

The variation of D is shown for alkali metal ions (Na" ) in Figure M.4 and shows a good fit with a constant pre-exponential Dq. Interestingly when the concentration of ions increases the diffusion rate increases as well. This is attributed to more lattice network discontinuities that fecilitate ion transport. Alkali diffusion is important to consider since electrical conduction of most commercial glasses results from sodium ions. While in many applications glass serves as an electrical insulator, ionic transport and hence conduction plays an important role in the manufecture of glass. Ionic conduction can be approximately estimated from Einstein s law ... 

Figure 1 shows the temperature variation of the ionic conductivities for several polymer-electrolyte systems. At room temperature they are typically 100 to 1000 times less than those exhibited by a liquid or the best ceramic- or glass-based electrolytes [6,8], Although higher conductivities are preferable, 100-fold or 1000-fold... 

Interesting systems, mainly with respect to solid-state optoelectronics and chalco-genide glass sensors (due to ionic conductivity effects) are found among the Group IIIB (13) and IVB (14) chalcogenides, such as the p-type semiconductors MSe (M = Ga, In, Sn), SnS, and GeX (X = S, Se, Te). Some of the IIIB compounds. 

I) The electrical (apparently ionic) conductance of the glass as a function of (a) chemical composition alkali metal ions increase the conductance to... 

Before treatment with alcohol, the ionic conductivity of lithium borate polymers was 6.23 X 10-5 to 2.07 X 10-7 Scm-1 at 50°C. The maximum ionic conductivity was observed for the polymer with a PE040o spacer unit. After the polymer reaction with alcohols, glass-transition temperatures of these polymers were found to be -52 to 39°C, which was higher than that of poly(lithium mesitylhydroborate) ( 69°C). 

Table 6 Glass Transition Temperature, Ionic Conductivity and VFT Parameters For Polymer/Salt Hybrids 10...

Rather specific structural features appear to be necessary for high ionic conductivity in crystalline solids, and as a result it may seem surprising that glasses can support high ionic conductivity. For example, a Li" conductivity of 0.16mScm at 25 °C for a glass with the composition... 

In the last 20 years, new sulphide, sulphate, molybdate, halide, etc., based compositions have been obtained in the glassy state (Ingram, 1987). They have much higher ionic conductivity than most oxide glasses at ambient temperature, e.g. from 10 to 10 S cm in the case of some lithium or silver conducting glasses (Fig. 4.1(h)). 

Fig. 4.1 Arrhenius plots for ionic conductivity, (a) General behaviour for ionically conducting glasses. At room temperature, the most conductive (Li or Ag ) have the lowest activation energy. For the less conductive glasses (Cs or mixed alkali glasses) the activation energy is around 1 eV. (b) Experimental data for Li conducting glasses (Souquet and Kone, 1986).

The glassy systems mentioned in Figs. 4.1(h) and 4.2 show that quite complex chemical compositions have been prepared in the glassy state. Up to three basic constituents are present in all ionically conducting glasses network formers, network modifiers and ionic salts, in different proportions. 

Such a chemical approach which links ionic conductivity with thermodynamic characteristics of the dissociating species was initially proposed by Ravaine and Souquet (1977). Since it simply extends to glasses the theory of electrolytic dissociation proposed a century ago by Arrhenius for liquid ionic solutions, this approach is currently called the weak electrolyte theory. The weak electrolyte approach allows, for a glass in which the ionic conductivity is mainly dominated by an MY salt, a simple relationship between the cationic conductivity a+, the electrical mobility u+ of the charge carrier, the dissociation constant and the thermodynamic activity of the salt with a partial molar free energy AG y with respect to an arbitrary reference state ... 

For a simple glass made of a network former and a network modifier, M2X, a large increase in ionic conductivity with alkali content results in a large increase of AGmjx. mainly from entropic origin. In the case of... 

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