Dynamics of mobile ions in glass - What do conductivity spectra tell us ?

Abstract

In glassy electrolytes, the diffusive motion of the mobile ions consists of thermally activated hops from site to site. Beyond this statement, little is known about the microscopic dynamics of ionic transport in glass, the problems originating mainly from the lack of long-range order. An important step forward has been made recently by employing the technique of conductivity spectroscopy in a frequency range that covers about fourteen decades, extending up to the far infrared. This particular experimental tool acts as a "microscope in time" resolving hopping processes down to the sub-picosecond time regime. The power of the method is exemplified for the case of a lithium-ion conducting lithium bromide-lithium borate glass, which is representative in many respects. Among the results obtained is the frequent oecurrence of correlated back-and-forth hopping processes as well as the finding that ions have preferences for optimally configured sites which play the role of stepping stones for translational diffusion.