Abstract
Niobium samples with residual resistivity ratios greater than 20,000 were prepared via a two‐step process. First, a fused salt electroplating process was used to prepare niobium having an exceptionally high purity with respect to the substitutional transition metal impurities tantalum and tungsten. Second, this electroplated niobium was vacuum degassed to remove the interstitial impurities, oxygen, nitrogen, and hydrogen. The major contributions to the residual resistivity after vacuum degassing were from the impurities nitrogen, tantalum, and tungsten. The electrical resistivity of these ultrahigh purity niobium samples can be calculated from the relation where represents the thermal contribution to the resistivity at the temperature and , , and represent respectively the concentrations in atomic per cent of nitrogen, tantalum, and tungsten. The value of for the vacuum degassed samples is given by where represents the partial pressure (Torr) of nitrogen in the vacuum system and represents the temperature (K) of the sample during outgassing.

This publication has 0 references indexed in Scilit: