Bulk layers of Nb 3 Ge have been deposited on copper substrates at 900°C by the hydrogen reduction of the chlorides of niobium and germanium with resistive T c 's as high as 22.5°K and current densities up to 1.8 × 10 6 A ‐ cm − 2 at 13.8°K. This paper provides a detailed description of the coating process as well as empirical correlations between deposition parameters and T c . Quantitative chlorination of Nb was found to be possible at T ≈ 250 ° C and for T > 900 ° C extending the range of delivery rates below those obtainable by powder feeding of NbCl 5 . Coatings in the range of 10–60 μm thick have been produced with a typical deposition efficiency of 50–65% for mass flow rates of the order of 1g of salt per minute. The superconducting transition temperature has been correlated with a parameter of the form mole ratio × dilution × Reynolds number 0.22 , where mole ratio is defined by moles Nb : moles ( Ge + O ) in the gas stream, and dilution by moles gas:moles salt. In addition, the relationship between mole ratio and dilution which determines the phase produced ( Nb 3 Ge or Nb 5 Ge 3 ) is defined over the region of major interest. Lattice spacings are presented over a range of T c 's, and microstructure and substrate adherence are discussed.
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Newkirk et al. (1976) studied this question.