The thermal conductivities of some dielectric solids at low temperatures (Experimental)

TLDR

At high temperatures, glass conductivity scales with specific heat, but at low temperatures it decreases more slowly. The study aimed to measure thermal conductivity of solids between 2 and 90 K using a newly described apparatus. The authors employed this apparatus to assess conductivity from 2 to 90 K and investigated lattice defect effects by neutron‑irradiating quartz crystals and monitoring conductivity changes. Results showed that glasses and dielectric crystals have a temperature range of nearly constant conductivity, Perspex behaves similarly, neutron‑irradiated quartz approaches glass conductivity which recovers after heating, and the findings support Klemens’ theory and the importance of Umklapp processes.

Abstract

An apparatus is described in which the thermal conductivity of solids can be determined at any temperature between 2 and 90°K. Several glasses and dielectric crystals have been measured. It had previously been found that at high temperatures the conductivity of glasses is proportional to the specific heat, but at low temperatures it falls off more slowly than the specific heat. The present experiments show that there is a temperature region in which the conductivity is nearly independent of temperature. A similar variation of conductivity is found for the thermo-plastic Perspex. The effect of lattice defects in crystals was studied by measuring the thermal conductivity of a quartz crystal before and after successive periods of neutron irradiation. After prolonged irradiation the conductivity approached, in both magnitude and temperature variation, that of quartz glass. Subsequent heating produced a substantial recovery in the conductivity. The results on both glasses and on crystals can be explained by the theory developed by Klemens (1951). Further measurements made on a corundum crystal confirm the importance of the ‘Umklapp’ processes, postulated by Peierls, in causing thermal resistance.