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 Ba/sub 8/-Ge/sub 46-x/-Co/sub x/ (x = 0, 4 and 6) were prepared by directly melting at 950/spl deg/C and then by solid-state reaction at 700 /spl deg/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/sub C1/ is about 170 Oe for the T/sub C/ = 4 K superconducting phase, and 500 Oe for the T/sub C/ = 10 K phase. In these compounds, Co-doping results in the suppression of T/sub 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.