Thermal Conductivity of High-Purity Thorium

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Abstract
The thermal conductivity and the electrical resistivity of three high-purity thorium samples with resistivity ratios 31, 140, and 480 have been measured as functions of temperature from 3 to 300 K. The samples were purified by the electrotransport method. Each of our higher-purity samples showed a large thermal conductivity maximum near 10 K and a constant thermal conductivity from 70 to 200 K. At low temperatures, the Lorenz ratios of samples having intermediate purity show, in addition to the linear term arising from electronic thermal conductivity, a quadratic term arising from phonon thermal conductivity limited by phonon-electron scattering. At higher temperatures, the phonon thermal conductivities of these samples vary inversely as the temperature owing to the dominance of unklapp phonon-phonon scattering. The ideal electronic thermal resistivity from 14 to 25 K was proportional to the square of the temperature as expected for electron-phonon scattering.

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