Thermal Conductivity of Some Amorphous Dielectric Solids Below 1°K

The thermal conductivities of nylon, Teflon, Kel-F, hard rubber, Epibond 100A, Epibond 104, and Pyrex have been measured below 1°K, generally in the range 0.8 to 0.1°K. In all cases the thermal conductivity decreases more rapidly than linearly with decreasing temperature. If this temperature dependence is assumed to result from intrinsic structure scattering and a single temperature independent scattering length, the resulting scattering lengths fall in the range 10−3 to 10−4 cm. Several of the materials studied, particularly Teflon, Epibond 104, and nylon, have significantly lower thermal conductivities in the temperature range investigated than does Pyrex, the material most commonly used for thermal isolation in the design of demagnetization cryostats.