Superconductivity to 21 K in intermetallic thorium-based boride carbides

We report the observation of superconductivity in intermetallic thorium-based boride carbides. For ThM2B2C, superconducting Tc's of 6 K (M=Ni), 6.5 K (M=Pt), and 14.5 K (M=Pd) have been measured. These compounds are isostructural with the recently reported LnNi2B2C superconductors. We have also observed bulk superconductivity in an as-yet-undetermined thorium-palladium-boron-carbon quaternary phase at 21.5 K. Critical-field measurements on the two palladium-based superconductors, as well as the pressure dependence of Tc for the 21.5 K superconductor, are reported. © 1994