Superconductivity in NbGe2 and Isostructural C-40 compounds

The superconductivity of NbGe2 and isostructural C-40 compounds has been studied in a quantitative manner. The high transition temperatures (T/sub c/=16 K) exhibited by sputtered films of NbGe2 are shown to be an intrinsic property of the compound and are attributed to the degree of order produced during the formation process. The roles of excess germanium and thermal effects are also discussed for NbGe2. One of the major conclusions established in this study is that a new crystal structure type, namely the hexagonal C-40 system, is superconducting. Four binary compounds are shown to exhibit superconductivity; they are NbGe2 (T/sub c/=16 K), NbSi2 (T/sub c/=2.9 K), Tasi2 (T/sub c/4.4 K), and TaGe2(T/sub c/=2.7 K). Even though superconductivity has been demonstrated on these compounds, the mechanism responsible for the superconductivity has not been established