Structure and physical properties of ternary uranium transition-metal antimonides U3MSb5 (M = Zr, Hf, Nb)

The ternary uranium transition-metal antimonides U3MSb5 (M = Zr, Hf, Nb) were prepared by arc-melting reactions followed by annealing at 800 deg. C, or by use of a Sn flux. These compounds extend the previously known series U3MSb5 (M = Ti, V, Cr, Mn) and RE3MSb5 (RE = La, Ce, Pr, Nd, Sm; M = Ti, Zr, Hf, Nb). The crystal structures of U3MSb5 were determined by single-crystal X-ray diffraction data (Pearson symbol hP18, hexagonal, space group P63/mcm, Z = 2; U3ZrSb5, a = 9.2223(3) A, c = 6.1690(2) A; U3HfSb5, a = 9.2084(4) A, c = 6.1629(3) A; U3NbSb5, a = 9.1378(4) A, c 6.0909(6) A). U3TaSb5 has also been identified in microcrystalline form (a = 9.233(3) A, c = 6.142(3) A). Four-probe electrical resistivity measurements on single crystals and dc magnetic susceptibility measurements on powders indicated prominent transitions that are attributed to ferromagnetic ordering. The Curie temperatures, T C, located from ac magnetic susceptibility curves, are 135 K for U3ZrSb5, 141 K for U3HfSb5, and 107 K for U3NbSb5