HREM on Tc=14.5 K superconducting ThPd2B2−xC

Abstract

The compound ThPd2B2C has been studied with high-resolution electron microscopy and electron diffraction. ThPd2B2_xC adopts the LuNi2BEC structure with a layer sequence (BrNi2-B=-LuC)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 ( < 50 nm) was observed to decrease up to about 0.5 nm when irradiated by the electron beam.

Structure and composition analysis of the phases in the system Th-Pd-B-C containing superconductors with Tc = 14.5 K and Tc = 21 K

“…(2) this phase is absent in the specimen 1331a which shows no superconducting transition at 14.5 K; (3) the structure as determined by HREM [ 8 ] indicates that this phase adopts the LuNi2BzC structure, a structure which has shown superconductivity for many analogous compounds. The plate-like morphology of ThPd2BEC is similar to the shapes of the crystals of LUNiEBEC [ 10 ] and YPdzBEC [ 6 ].…”

“…They concluded that the superconducting phase is YPd2B2C having a structure quite similar to that of LuNi2B2C. Sarrac et al [ 3 ] have reported the presence of two superconducting phases in the system Th-Pd-B-C, one with composition YPd2B2C having a Tc of 14.5 K and the LuNi2B2C structure [ 3,8 ] and one with a Tc of 21 K whose composition and structure are not known. The problem of identifying the 21 K phase in the system Th-Pd-B-C seems to be similar to the identification of the 23 K phase in the system Y-Pd-B-C, since in both cases it is difficult or impossible to synthesize single-phase material.…”

“…A HREM study of ThPd2B2C has been reported previously [ 8 ]. It showed that ThPd2B2C adopts a LuNiEBEC-like structure, possibly with a deficiency in B.…”

“…The composition is determined by EPMA to be ThPd2BEC. The structure as determined by HREM [ 8 ] indicates that this phase adopts the LUNiEBEC structure; it is schematically presented in Fig. 3.…”

“…Because of the low scattering crosssection of B the effect of presence or absence of B is small and cannot be distinguished based on fits with the experimental image. A detailed study of this structure will be presented elsewhere [ 12 ].…”