La6Pd2+xSb15 (x = 0.28): A rare-earth palladium intermetallic compound with extended pnictogen ribbons

A new intermetallic ternary compound La6Pd2.28Sb15 was synthesized from the reaction of lanthanum and palladium metals in a molten antimony flux. The compound crystallizes in the orthorhombic space group Immm with a ​= ​4.3082(9) Å, b ​= ​15.399(3) Å and c ​= ​19.689(4) Å. The crystal structure contains a three-dimensional framework of Sb squares and ribbons that extend along the a axis, including complex Sb–Sb bonding. La6Pd2.28Sb15 is diamagnetic, with a magnetic susceptibility weakly dependent on temperature (T). The resistivity (ρ) decreases when lowering the temperature, indicating metallic behavior, and at low temperatures ρ depends quadratically on T. Interestingly, both the Hall resistivity and magnetoresistance present a nonlinear dependence on the applied magnetic field, suggesting a multiband behavior. This is supported by density-functional electronic structure calculations which show a complex Fermi surface originated in the antimonide substructures and containing both electron and hole pockets as well as open sheets.