Abstract
RhPb2 (rhodium dilead) is a superconductor crystallizing in the CuAl2 structure type (space group I4/mcm). The Rh and Pb atoms are located at the 4a (site symmetry 422) and 8h (m.2m) sites, respectively. The crystal structure is composed of [RhPb8] anti-prisms, which share their square faces along the c axis and the edges in the direction perpendicular to the c axis. We have succeeded in growing single crystals of RhPb2 and have re-determined the crystal structure on basis of single-crystal X-ray diffraction data. In comparison with the previous structure studies using powder X-ray diffraction data [Wallbaum (1943 ▸). Z. Metallkd. 35, 218-221; Havinga et al. (1972 ▸). J. Less-Common Met. 27, 169-186], the current structure analysis of RhPb2 leads to more precise unit-cell parameters and fractional coordinates, together with anisotropic displacement parameters for the two atoms. In addition and likewise different from the previous studies, we have found a slight deficiency of Rh in RhPb2, leading to a refined formula of Rh0.950 (9)Pb2.
Highlights
A large number of binary intermetallic compounds with the CuAl2 structure type have been reported (Wallbaum, 1943; Havinga et al, 1972; Havinga, 1972), and several of them exhibit superconductivity (Gendron & Jones, 1962)
The Rh atom is surrounded by eight Pb atoms occupying the edges of the [RhPb8] antiprism, and two Rh atoms are spaced along the c axis at a distance of half of the unit-cell parameter c
(Table 1; Fig. 1b, Pb—Pbix); all Pb—Pb distances belonging to the shared square faces of the [RhPb8] antiprism are equal (Fig. 1b, Pb—Pbx), while the Pb—Pb distances belonging to the sides of the triangle of the [RhPb8] antiprism are all different (Fig. 1c, Pb—Pbx, Pb—Pbxi and Pbx-–Pbxi)
Summary
A large number of binary intermetallic compounds with the CuAl2 structure type have been reported (Wallbaum, 1943; Havinga et al, 1972; Havinga, 1972), and several of them exhibit superconductivity (Gendron & Jones, 1962). -RhPb2 adopting the -PdBi2 structure type (space group I4/mmm) has been reported as a candidate material for topological superconductors (Zhang et al, 2019), and RhPb2 crystallizing in the CuAl2 structure type has attracted much attention. While the previous powder X-ray studies of RhPb2 (Wallbaum, 1943; Havinga et al, 1972) used polycrystalline material prepared by a melting method, we have grown RhPb2 single crystals by application of a vertical pulling mechanism using an infrared mirror furnace. We report on the redetermined crystal structure of RhPb2 based on single-crystal X-ray data
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