Dynamic light scattering study of nonexponential relaxation in supercooled 2Ca(NO3)2⋅3KNO3

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Abstract
We have performed depolarized dynamic light scattering (photon correlation) measurements on the ionic glass forming mixture 2Ca(NO3)2⋅3KNO3 above its glass transition in the temperature range 68–86 °C. We find the relaxation function is a stretched exponential. The average relaxation time follows an Arrhenius temperature dependence and can be related to motions on a molecular scale. The width parameter β does not vary with temperature and is β=0.40±0.05. Combination of our β data with other literature values shows that β evolves with temperature over a larger range. At high temperature, β crosses over from β=1 to βTg. This behavior corresponds well with recent theory relating the glass transition to the ramification of phase space but it implies that the percolation of phase space occurs well above Tg.