Effect of impurities on the residual resistance of niobium

The effect of three impurities, Ru, Re, and Os, on the electrical resistance of niobium at 20.4 and 77.3 °K was studied. Using 99.95% pure niobium with residual resistivity ratio ρ0/ρ293 = 7·10−2 specimens were prepared over the concentration range of 0.3 to 5% by weight. At 20.4 °K values of Δ ρ/c of 2.7, 2.2, and 1.4 μΩ·cm/at. % were found for Ru, Os, and Re, respectively. Data for 15 other impurity elements in niobium, found in the literature and often very approximate, are presented.