The Preparation of High T c Nb3Ge Superconductors by Chemical Vapor Deposition

Abstract
Bulk layers of have been deposited on copper substrates at 900°C by the hydrogen reduction of the chlorides of niobium and germanium with resistive 's as high as 22.5°K and current densities up to at 13.8°K. This paper provides a detailed description of the coating process as well as empirical correlations between deposition parameters and . Quantitative chlorination of Nb was found to be possible at and for extending the range of delivery rates below those obtainable by powder feeding of . 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 number0.22, where mole ratio is defined by 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 ( or ) is defined over the region of major interest. Lattice spacings are presented over a range of 's, and microstructure and substrate adherence are discussed.