Theory. Relaxation Dynamics in Disordered Ionic Conductors

Structurally disordered solid electrolytes, both crystalline and glassy, as well as ionic melts, exhibit a set of spectroscopic peculiarities that are at variance with the predictions of simple random‐hopping models. Typically, stretched exponential functions are encountered where ordinary exponential functions are expected. The effect has come to be called “universal dynamic response.” In this paper, it is traced back to a mean square displacement which, in a broad time regime, varies as time to the power of β, with 0 < β < 1. Computer simulations as well as model considerations show that this particular shape of the mean square displacement is caused by the frequent occurrence of correlated forward‐backward hopping sequences. The latter processes result from the mutual repulsive Coulomb interaction of the mobile ions.

Is there a “Universal” Explanation for the “Universal” Dynamic Response?

Funke

1991

Frequency‐Dependent Conductivity. Ionic Conductivity and Memory Effects in Glassy Electrolytes

Ingram

Maass

Bunde

1991

Ionic conductivities in glass depend very strongly on temperature, frequency and glass composition. In the absence of well‐defined structure, the behaviour of vitreous electrolytes may be strongly influenced by various “memory effects”. These include the classical ion‐atmosphere effect which tends to return ions to their starting positions – and hence causes a reduction in ion mobilities – and a newly formulated site memory effect, which effectively creates “cation vacancies”, and leads to conductivity enhancement. The site memory effect gives a straightforward explanation for compositional variations in conductivity (including the mixed alkali effect) and points up a connection with “strength” and “fragility” concepts of glass/melt structure.

IV. Transport Phenomena, Properties of Glass Surface and Corrosion. Ion and polaron conducting glasses

Cramer

1996

Conductivity spectra, (~( w ) , covering wide frequency ranges up to the mid infrared, have been taken of various glasses at different temperatures. The systems studied include the ion-conducting glasses 0.30 Na20. 0.70 B2O3, 0.30 Li20.0.70 B203 and B20,.0.56 Li,O.O.45 LiBr as well as the polaron conducting glass 0.2 P2O5.O.8 (0.89V20,.0.11 V,O,). In the case of the ion-conducting glasses it is possible to separate vibrational and hopping spectra from each other. The resulting hopping spectra display high-frequency plateaus; in the dispersive regime, two power-law exponents are observed, one being smaller, the other larger than unity. In contrast, the dispersive conductivity of the polaron conducting glass shows a simple single-power-law behavior with an exponent smaller than one. The interpretation of the spectra includes the idea of different "target" sites for the mobile species. A model concept for ion and polaron transport in glasses is proposed.