Superconductivity in Ta-doped Zr$_{\mathrm{5}}$Ge$_{\mathrm{3}}$ System

Inspired by the discovery of first superconductor Zr$_{\mathrm{5}}$Sb$_{\mathrm{3}}$ in the large hexagonal Mn$_{\mathrm{5}}$Si$_{\mathrm{3}}$-type compounds, we have carried out systematical doping studies in the Ta-doped Zr$_{\mathrm{5-x}}$Ta$_{\mathrm{x}}$Ge$_{\mathrm{3}}$ (0 $\le $ x $\le $ 5) system. X-ray diffraction analysis has shown a clear phase transition from hexagonal Mn$_{\mathrm{5}}$Si$_{\mathrm{3}}$-type structure to tetragonal W$_{\mathrm{5}}$Si$_{\mathrm{3}}$-type structure occurring when x\textgreater 3. Superconductivity up to 4.5K is observed, on the other hand, when Ta doping level is 0.5$\le $x$\le $2. The superconductivity is further demonstrated from both magnetic and electrical resistivity measurements with type-II superconductors and upper critical field \textasciitilde 5000 Oe. The detailed synthesis and characterizations will be presented and discussed.