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) angstrom, b = 15.399(3) angstrom and c = 19.689(4) angstrom. 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 (rho) decreases when lowering the temperature, indicating metallic behavior, and at low temperatures rho 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.