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A time-of-flight inelastic neutron scattering study of Ca0.4K0.6(NO3)1.4 of the temperature dependence of the dynamic structure factor revealed a clear frequency-independent signature of the glass transition at the conventional transition temperature Tg. Above Tg the data combined with our previous neutron spin echo results display two relaxation processes at well-separated frequencies. The faster process was now found to be consistent with a scaling behaviour corresponding to a critical-type slowing-down when approaching a certain temperature T0, as predicted by recent mode coupling theories. The variation of various properties consistently points to a critical temperature T0 of about 30 K above Tg = 333 K.

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The thermal properties of (KBr)l "(KCN)"single crystals have been studied between 0.05 and 100 K over the entire compositional range. For 0.25 & x & 0.70, these crystals have the thermal conductivity that is typical for all structurally disordered, amorphous solids. The same holds for the low-temperature specific heat, which varies linearly with temperature, and logarithmically with the measuring time. Through a quantitative analysis it is shown that these mixed crystals represent an excellent example of two-level-system excitations of variable number densities, depending on the choice of x. Therefore, these crystals can serve as a model for the exploration of the low-energy excitations which are characteristic for all amorphous solids.

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