Ion transport in the fragile glass former ${3\mathrm{K}\mathrm{N}\mathrm{O}}_3$-2Ca(${\mathrm{NO}}_3$${)}_2$

The molten salt ${3\mathrm{K}\mathrm{N}\mathrm{O}}_3$-2Ca(${\mathrm{NO}}_3$ ${)}_2$ has been studied in the frequency range 5 mHz<ν<40 GHz and for temperatures 10 K<T<500 K using impedance spectroscopy. It is found that in the microwave regime the dynamic conductivity traces the primary response. In the radio- and audio-frequency ranges the mobile ion relaxation becomes increasingly decoupled and the time scale and stretching of the response as determined from electrical modulus spectra differ from those obtained by spectroscopies probing the structural response. For T≳360 K minima are detected in the dielectric loss that make possible a comparison with recent mode-coupling theories of the glass transition. The absence of analogous minima in nonionic supercooled liquids is discussed. © 1996 The American Physical Society.