Beschreibung:
<jats:title>Abstract</jats:title><jats:p>The thermal conductivities of niobium and tantalum single crystals of different impurity contents are measured between 0.3 and 20 K. Below about 1 K the thermal conductivities of all specimens vary with temperatures as <jats:italic>T</jats:italic><jats:sup>3</jats:sup>, but the magnitude of the thermal conductivity decreases with increasing impurity content. A careful investigation of the defect structure of the specimens leads to the conclusion that interstitial and substitutional impurities give rise to a thermal resistance even at low temperatures.</jats:p>