ELASTIC PROPERTIES OF SEVERAL AMORPHOUS SOLIDS AND DISORDERED CRYSTALS BELOW 100 K

We have measured the internal friction and speed of sound variation at temperatures between 60 mK and room temperature for amorphous CdCeAs2 , Polystyrene, and Stycast 2850FT epoxy, and the disordered crystals ( ZrO2)(0.89)(CaO)(0.11) and (CaF2)(0.74)(LaF3)(0.26). A comparison of o ur results with an extensive review of previously published data shows a remarkable similarity in the internal friction of disordered solids below similar to 5 K. The low temperature elastic behavior of these s olids is adequately described by the standard tunneling model, from wh ich one finds a nearly universal density of tunneling states for glass es. Internal friction above similar to 10 K for different materials, h owever, displays a wide range of magnitudes and temperature dependence that is far from universal. Attempts to directly link the tunneling s tates observed by internal friction at low temperatures to configurati onal states of localized oscillators existing at high temperatures mus t take into account this striking variation among disordered solids ab ove 10 K.