Preparation and Electrical Resistivity of Ultrahigh Purity Niobium

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

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