Superconductivity at 10 K in (Ge, Ba)-based compounds

This study focused on (Ge, Ba)-based compounds with Co-doping, and found superconductivity at 10 K for these (Ge, Ba)-based compounds. Materials with compositions Ba₈-Ge_46-x-Co_x (x = 0, 4 and 6) were prepared by directly melting at 950°C and then by solid-state reaction at 700 °C. X-ray diffraction shows that these materials are mixtures of several phases. The magnetic susceptibility of the x = 0 sample shows that there are two superconducting transitions, at about 10 K and 4 K. Electrical transport measurement also confirmed the existence of two superconducting transitions. The M-H curves show that the first critical field H_C1 is about 170 Oe for the T_C = 4 K superconducting phase, and 500 Oe for the T_C = 10 K phase. In these compounds, Co-doping results in the suppression of T_C, from 10 K to 7 K. The superconducting volume fraction also decreases with increasing Co-doping. For Co-doped samples, there is no 4 K superconducting transition.