Characterization of the Binary Uranium and Thorium Tellurides U₇Te₁₂ and Th₇Te₁₂

Abstract

Single crystals of U 7 Te 12 and Th 7 Te 12 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 P 6̄ (No. 174), Z = 1. The cell constants are a = 12.312(1) Å and c = 4.260(1) Å for U 7 Te 12 and a = 12.300(2) Å and c = 4.566(1) Å for Th 7 Te 12 . 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 [001] 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. U 7 Te 12 exhibits ferromagnetic ordering below 54 K and a semimetallic type conductivity.