Fast Dynamics in CKN and CRN Investigated by Dielectric Spectroscopy

Dielectric spectroscopy up to a frequency of 380 GHz has been performed on the molten salts $\left[\mathrm{Ca}\right({\mathrm{NO}}_3{)}_2{]}_{0.4}[{\mathrm{KNO}}_3{]}_{0.6}$ (CKN) and $\left[\mathrm{Ca}\right({\mathrm{NO}}_3{)}_2{]}_{0.4}[{\mathrm{RbNO}}_3{]}_{0.6}$ (CRN). For the first time, conclusive results for the transition region between the $\alpha$-relaxational and the far-infrared response have been obtained in ionically conducting glass formers using dielectric spectroscopy. In addition to the dielectric loss, we present data for the reactive part of the dielectric constant. At high temperatures and the highest frequencies investigated, both materials exhibit a sublinear spectrum. For CRN the dielectric loss follows a power law with a frequency exponent 0.2 over three decades of frequency.