We report on an investigation of superconductivity and magnetism in the series of compounds M(Formula presented)Pb (M=rare earth, Th, U) through measurements of electrical resistivity, magnetic susceptibility, specific heat, and lattice parameters. Both single crystals and polycrystalline samples were studied. The compound (Formula presented)Pb was examined for possible heavy-fermion behavior, and found to exhibit antiferromagnetic order below T=35 K. © 1996 The American Physical Society.

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.

The compound ThPd2B2C has been studied with high-resolution electron microscopy and electron diffraction. ThPd2B2-xC adopts the LuNi2B2C structure with a layer sequence (ByNi2BzLuC)n in which the B composition and the exact position of the C are still uncertain. No intergrowths or planar defects are observed. The c-axis in the thinner parts of the crystals (<50nm) was observed to decrease up to about 0.5 nm when irradiated by the electron beam. © 1994.

Several specimens in the system Th-Pd-B-C with nominal compositions ThPd3B2C and ThPd3B3C (as melted and annealed), containing superconducting phases exhibiting Tc's of 14.5 K and 21 K, have been studied with EPMA, electron diffraction, EDX element analysis and HREM. A number of phases (approximate compositions are given) have been observed: (1) ThPd2B2C, I-centered tetragonal, a = 0.375, c = 1.07 nm, which can be related to the Tc of 14.5 K; (2) ThPd0.65B4.7, P-type cubic, a = 0.42 nm, with short-range ordered superstructure resulting in diffuse streaks in the electron-diffraction pattern; this phase is suggested to be the 21 K superconducting phase; (3) ThPd3 P-type hexagonal, a = 0.58, c = 0.98 nm; (4) ThPd8B3, I-centred orthorhombic a = 0.84, b = 0.90, c = 1.67 nm; (5) ThPd3B2C, with unknown structure; (6) ThB4, tetragonal a = 0.72, c = 0.41 nm; (7) graphitic C. Annealing of the specimen ThPd3B2C at 1050°C results in the disappearance of ThPd2B2C and the loss of the Tc at 14.5 K but a strong increase of the 21 K superconducting fraction with a corresponding strong increase of the phases ThPd0.65B4.7 and ThPd3. HREM indicates that ThPd0.65B4.7 adopts a modified CaB6 structure in which the cube face, 1 2, 1 2, 0, which is vacant in CaB6, is partially occupied by Pd with the removal of some B atoms. The superstructure indicates a short-range ordering (clustering) of the Pd atoms. © 1994.