Characterization of the Binary Uranium and Thorium Tellurides U7Te12 and Th7Te12
journal contributionposted on 05.09.1998, 00:00 by O. Tougait, M. Potel, H. Noël
Single crystals of U7Te12 and Th7Te12 were obtained by chemical vapor transport reactions in evacuated and sealed quartz tubes, starting from a slightly deficient tellurium stoichiometry and using iodine as the transporting agent in a temperature gradient of 1030−1000 °C. Their crystal structures were solved in the noncentrosymmetric hexagonal space group P6̄ (No. 174), Z = 1. The cell constants are a = 12.312(1) Å and c = 4.260(1) Å for U7Te12 and a = 12.300(2) Å and c = 4.566(1) Å for Th7Te12. The three nonequivalent actinoid (A = U, Th) atoms per unit cell, A(1), A(2), and A(3), occupy 1a, 3k, and 3j Wyckoff positions and the four nonequivalent tellurium atoms occupy two 3k and two 3j positions. All the actinoid atoms are centered in tricapped (A(1)) or bicapped (A(2), A(3)) tellurium trigonal prisms, which form infinite columns running along the  direction. The bicapped trigonal prisms around A(2) and around A(3) are linked also in both cases by edge-sharing, to form large distorted hexacapped trigonal prisms. U7Te12 exhibits ferromagnetic ordering below 54 K and a semimetallic type conductivity.