Thermal Conductivity of Vitreous Silica at Low Temperatures

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Abstract
The thermal conductivity of a number of samples of vitreous silica has been measured between 1.5 and 20 K and between 65 and 300 K. The specimens were obtained from a number of manufacturers and were all high-purity optical-quality material. Above 65 K, the thermal conductivities of all the specimens were found to be identical. Below 20 K, the thermal conductivities of four synthetic silicas, Englehard Suprasil and three types of Corning silica were the same, but the thermal conductivities of the samples made by fusing rock quartz were quite different. These differences were found to be as large as 50% at 2 K. Impurities in small concentrations have no significant effect on the thermal conductivity. According to one theory, long-range (∼ 100 Å) spacial correlations in the phonon scattering resulting from the small amount of long-range order remaining in an amorphous material may be the most important factor in determining the thermal conductivity of glasses at low temperatures, and can, at least in principle, account for the difference between the various silicas.

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