Structure and superconducting properties of Nb3Ge prepared in a UHV system
Abstract
Nb3Ge films are prepared by coevaporation of Nb and Ge under well defined and controlled conditions. The formation of the Al5 Nb3Ge phase is studied by varying the processing parameters – composition, deposition temperature, and impurity gas background – systematically. Single phase samples with Tc, onsets as high as 21.5 K and lattice parameters of 0.5148 nm only be obtained in an environment with no added impurities and a Ge concentration of 23.8 at%. Oxygen as impurity gas enhances Tc, slightly in samples of the optimal composition, whereas hydrogen as impurity gas does not affect the formation and the Tc, of the Al5 phase at all. The structure, (lattice parameters, grain sizes, and phases present) and the superconducting properties (Tc, Hc2(O)) of the samples show a systematic correlation of the preparation parameters and the physical properties. The experimental results are explained qualitatively within the frame of the linear chain model of Al5 superconductors combined with the introduction of anti‐site defects. Copyright © 1981 WILEY‐VCH Verlag GmbH & Co. KGaA