Elastic properties of several amorphous solids and disordered crystals below 100 K

Abstract

We have measured the internal friction and speed of sound variation at temperatures between 60 mK and room temperature for amorphous CdGeAs2, 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 our results with an extensive review of previously published data shows a remarkable similarity in the internal friction of disordered solids below ∼5 K. The low temperature elastic behavior of these solids is adequately described by the standard tunneling model, from which one finds a nearly universal density of tunneling states for glasses. Internal friction above ∼10 K for different materials, however, displays a wide range of magnitudes and temperature dependence that is far from universal. Attempts to directly link the tunneling states observed by internal friction at low temperatures to configurational states of localized oscillators existing at high temperatures must take into account this striking variation among disordered solids above 10 K.