A Low Temperature Investigation of Amorphous Materials

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The low-temperature properties of amorphous solids are remarkably different from the well-understood behavior of crystalline materials. At temperatures below 1K this difference is caused by localized excitations. It is not known what the excitations are for any amorphous solid, but they appear to arise from the tunneling motion of some entity having atomic size. A purpose of the proposed research is to further establish the role of the localized excitations in seveal low-temperature properties, to determine how to manipulate or control the excitations, and eventually to identify the excitations in certain amorphous systems. At higher temperatures, both the specific heat and thermal conductivity of glassy solids again exhibit unusual behavior normally not found in a crystal. The proposed research will also attempt to establish a qualitative explanation for these features. The experimental approach involves measurements of specific heat, thermal conductivity, thermal expansion, and ultrasonic and dielectric dispersion on samples of silicate glasses, amorphous polymers, and orientationally disordered solids as the disordered matrix of each sample is modified systematically.