Short time relaxation processes in liquids from viscosity and light scattering studies in molten KCl 2BiCl3

Brillouin scattering, viscosity, and calorimetric studies of the congruently melting glass-forming compound KCl⋅2BiCl3 have been made to clarify and extend a pattern of relaxation behavior seen over wide temperature ranges in a recent study of the simple ionic liquid system KNO3 +Ca(NO3)2. Viscosity data for the two systems covering nearly four orders of magnitude superimpose when scaled by the glass temperature Tg ratio, and comparable parallels are seen in the hypersonic absorption behavior. Sound velocity and absorption data are consistent with single relaxation time kinetics at high temperature in accordance with findings for the KNO3 +Ca(NO3)2 system. In each system high temperature Arrhenius behavior breaks down when τ>10−11s. It is shown in the present system that this is forced by the approach of the system to a thermodynamic limit where liquid and crystalline entropy contents would equalize: the limit falls only 26 K below Tg. A relationship to the behavior of argon is considered.