Complete conductivity spectra of fast ion conducting silver iodide silver selenate glasses

We present complete dynamic conductivity spectra of the fast-ion conducting glass 0.48(AgI)(2) . 0.52Ag(2)SeO(4). The spectra were recorded at frequencies between 4 Hz and 10 THz and at temperatures between 93 K and 573 K. This temperature range covers the glassy and molten state of matter. In the spectra, we can clearly distinguish between the hopping conductivity at low frequencies, and the vibrational regime at very high frequencies. We remove the vibrational contribution and obtain spectra which are then entirely interpreted in terms of the hopping motion of the silver ions ('complete hopping spectra'). To describe these complete hopping spectra a superposition of two power laws is needed. One of them is the 'Jonscher power law' with an exponent 0.62, while the additional power law has an exponent larger than one. Both power-law components are thermally activated. The low-frequency hopping conductivities of 0.48(AgI)(2) . 0.52 Ag2SeO4 are consistent with the 'master curve', recently obtained by Roling et al. The interpretation of our hopping spectra includes the idea of different 'target sites for the mobile silver ions as described in the unified site relaxation model as well as the existence of 'Coulombic traps' which is an essential feature of the counter-ion model.