Polyborides with Th2NiB10-Type Structure: Synthesis, Crystal Structure, and Magnetic and Electrical Properties

The new rare-earth nickel polyborides R2NiB10 (R=Y, Ce-Nd, Sm, Gd-Ho) were prepared by reacting cold-pressed pellets of the elemental components in an arc-melting furnace, followed by annealing in evacuated silica tubes. They crystallize with the orthorhombic Th2NiB10-type structure, which was refined from X-ray powder diffractometer data of Ce2NiB10 (a=565.4(1) pm, b=1125.8(2) pm, c=419.6(1) pm) and Nd2NiB10 (a=561.4(1) pm, b=1119.2(2) pm, c=417.7(1) pm). The magnetic properties of these polyborides and also of Th2CoB10 and Th2NiB10 were determined with a superconducting quantum interference magnetometer between 2 and 400 K with magnetic flux densities up to 5.5 T. Y2NiB10, Th2CoB10, and Th2NiB10 are Pauli paramagnetic. The others show Curie-Weiss behavior with magnetic moments corresponding to those of the free R3+ ions, with the exception of Ce2NiB10, where cerium has a mixed valence and Sm2NiB10 with the van Vleck paramagnetic Sm3+ ion. Antiferromagnetic order was observed for the compounds R2NiB10 (R=Pr, Nd, Sm, Gd-Ho) with NTel temperatures ranging between 8 K for Pr2NiB10 and 33 K for Gd2NiB10. Tb2NiB10, Dy2NiB10, and Ho2NiB10 are metamagnetic. Electrical resistivity measurements reflect the magnetic ordering temperatures and indicate metallic behavior for all compounds.