Dielectric losses in solids at cryogenic temperatures

Measurements were made of the permittivity and loss tangent of polyethylene, poly(4-methyl pentene-1), polyethylene terephthalate, polyvinyl chloride (containing 33% tritolyl phosphate), poly-¿-undecanolactum, cellulose triacetate and insulating paper for temperatures between 4.2 and 295°K over a frequency range from 47Hz to 89.5kHz. In polyethylene and poly(4-methyl pentene-1), a single small absorption region (maximum value, 1¿2×10¿4 was observed in the temperature range 150¿200°K. The loss tangent of polyethylene decreased to a constant value (~2×10¿5) near absolute-zero temperature, whereas, in the case of poly(4-methyl pentene-1), below 70°K it increased with increasing frequency and decreasing temperature. With the exception of polyvinyl chloride, which did not exhibit any distinct absorption regions, the remaining materials investigated possessed one or more loss regions with a maximum loss tangent between 4×10¿3 and 3×10¿4. The peaks occurred in the temperature range 150¿300°K. The loss tangent of these materials decreased to 1¿3×10¿4 as the temperature was reduced to 4.2°K, with the exception of poly-¿-undecanolactum, for which it was 3×10¿5