The crystal structure of SnYb3Rh4Sn12, a new ternary superconducting stannide

The crystal structure of superconducting SnYb3Rh4Sn12 has been determined from single-crystal X-ray diffraction data. This compound is cubic, space group Pm3n, ao = 9.676 A (1) and has two formulae per unit cell. The structure was solved from Patterson and subsequent Fourier synthesis. The least squares refinement was based on 375 independent reflections. The final R and wR factors were 0.015 and 0.014, respectively. The two Sn(1) atoms occupy the 2a (000) positions, the six Yb atoms the 6d (1/4, 1/2, 0) positions, the eight Rh atoms the 8e (1/4, 1/4, 1/4) positions and the twenty-four Sn(2) atoms the 24k (O,y,z) positions (y approx = 0.31, z approx = 0.15). The Sn(2) atoms form a tridimensional array of corner-sharing trigonal prisms whose centers are occupied by the Rh atoms. The Sn(1) and the Yb atoms occupy the icosahedral and cuboctahedral holes of this array, respectively. They form a sublattice which has the arrangement found in the structure of the A15 compounds. The structure of SnYb3Rh4Sn12 can be described as containing two interpenetrated structures, namely Yb3Sn and RhSn3, or as having an A15 arrangement of clusters of atoms such as (SnSn12) and (YbSn12). These clusters are bound together by face-sharing among them; and by the Rh atoms. An analogy is drawn between SnYb3Rh4Sn12 and the perovskite-like ternary oxide A'A3B4O12. 7 ref.--AA