ION DYNAMICS IN GLASS-FORMING SYSTEMS .2. CONDUCTIVITY SPECTRA ABOVE THE GLASS TRANSFORMATION TEMPERATURE

The conductivity spectra of three supercooled glass-forming molten sal ts, LiCl . 7H(2)O, Ca(NO3)(2) . 4H(2)O and 3KNO(3) . 2Ca(NO3)(2), have been taken at various temperatures above To. The data cover a wide fr equency range from a few MHz to the far infrared. The d.c. conductivit ies exhibit Vogel-Fulcher-Tammann temperature dependences, but with in creasing frequency a change to Arrhenius is observed. The crossover oc curs along with the onset of the power-law frequency dependence of the conductivity. Increasing the frequency further up to the far infrared , we observe a second crossover, now into a nu(2) frequency dependence due to the excitation of vibrational motion. The vibrational contribu tions can be subtracted out of the spectra. This has been carefully do ne for 3KNO(3) . 2Ca(NO3)(2). The resulting non-vibrational conductivi ty attains a thermally activated 'high-frequency' plateau at about 1 T Hz, as in a solid electrolyte. On a short time scale, the dynamics of glass-forming fragile melts is, indeed, found to be very similar to th at of glass.