Structural chemistry and physical properties of ternary compounds R6Ni15As10, RÂ =Â Y, Sm, Gd, Tb, Dy

The ternary rare-earth nickel arsenides R6Ni15As10 (R = Y, Sm, Gd, Tb, Dy) were synthesized from the elements by reaction at elevated temperatures. They were found to crystallize with a hexagonal structure which was determined from single-crystal X-ray data in case of Tb6Ni15As10, space group P63/m, Z = 2, a = 17.005(1) Å and c = 3.8877(2) Å. The crystal structure for the isostructural compound Gd6Ni15As10 has been determined using X-ray powder diffraction data (full profile refinement: a = 17.0350(4) Å and c = 3.9183(1) Å). These compounds belong to a large family of hexagonal structures with a metal to metalloid ratio of 2:1. The paramagnetism of these compounds is only due to the lanthanoid 4f magnetic moment, whereas nickel is non-magnetic. At low temperatures the samples undergo magnetic transitions, anti-ferromagnetic in case of the Sm and Gd ternaries with TN = 15 and 24 K and ferromagnetic for Tb6Ni15As10 with TC = 12 K, respectively. The temperature dependence of the electrical resistivity, ρ(T), reflects the metallic character of these compounds. Characteristic changes of the slopes of the ρ(T) plots confirm the magnetic transitions.