Superconductivity in Mo5GeB2 with a tetragonal structure

The discovery of 39 K superconductivity in MgB2 and the recent observations of high-Tc superconductivity in the high-pressured hydrides motivate ones to search for new superconductors in the compounds containing H or B light element. In this article, we chose the heavier Ge to replace the Si in the ternary borides Mo5SiB2 with the Cr5B3 type tetragonal structure, a relative new group borosilicate superconductors, and prepared Mo5GeB2 polycrystalline sample. By the combination of resistivity, magnetization, and specific heat measurements and band calculations, we determine its superconducting parameters. It was found that Mo5GeB2 is a type II superconductor, with the critical temperature Tc = 5.4 K, and the Ginzburg-Landau (GL) parameter kGL(0) = 4.2. The estimated electron-phonon coupling constant λph (0.57) and the specific heat jump △Cel/γnTc (1.33) demonstrate that Mo5GeB2 is a weak-coupling, single-gap phonon-mediated superconductor. Band calculations reveal that Mo5GeB2 has a similar density of state (DOS) near Fermi energy to that of Mo5SiB2 with the same Tc, but smaller than that Mo5PB2 with Tc = 9.2 K.