RE8Rh17Sb14 (RE = La, Ce, Pr, Nd) with a CaBe2Ge2-related superstructure through rhodium–antimony-ordering and vacancy formation

The new antimonides RE8Rh17Sb14 (RE = La, Ce, Pr, Nd) were synthesised by arc-melting. Crystals can be grown in a high-frequency furnace. The RE8Rh17Sb14 phases were characterized by powder X-ray diffraction. They crystallize with a tetragonal, CaBe2Ge2-related superstructure which was refined for Ce8Rh17Sb14 on the basis of single crystal X-ray diffractometer data: I4cm, a = 1239.8 (3), c = 2101.8 (8) pm, wR = 0.065, 2924 F values, and 109 parameters. The rhodium and antimony atoms and vacancies show full ordering on the [Be2Ge2] substructure, leading to a composition of Ce8Rh17Sb14CeRh2.13Sb1.75. The superstructure formation is discussed on the basis of a group-subgroup scheme together with the related structures of CePt2+xSb2−y, CeNi1.91As1.94 and URh1.6As1.9. Temperature dependent susceptibility measurements show Pauli paramagnetism for La8Rh17Sb14 and Curie–Weiss paramagnetism for RE8Rh17Sb14 (RE = Ce, Pr, Nd). No magnetic ordering was detected down to 2.5 K.

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► Synthesis of new RE8Rh17Sb14 antimonides.
► Group-subgroup relation with the CaBe2Ge2 type in the Bärnighausen formalism.
► Superstructure formation through vacancy ordering.