Crystal structure and electronic properties of the new compounds, U6Fe16Si7 and its interstitial carbide U6Fe16Si7C

摘要

The new compounds U6Fe16Si7 and U6Fe16Si7C were prepared by arc-melting and subsequent annealing at 1500 degrees C. Single-crystal X-ray diffraction showed that they crystallize in the cubic space group Fm (3) over barm (No. 225), with unit-cell parameters at room temperature a = 11.7206(5)angstrom for U6Fe16Si7 and a = 11.7814(2)angstrom for U6Fe16Si7C. Their crystal structures correspond to ordered variants of the Th6Mn23 type. U6Fe16Si7 adopts the Mg6Cu16Si7 Structure type, whereas U6Fe16Si7C crystallizes with a novel "filled" quaternary variant. The inserted carbon is located in octahedral cages formed by six U atoms, with U-U interatomic distances of 3.509(1)angstrom. Insertion of carbon in the Structure of U6Fe16Si7 has a direct influence on the U-Fe and Fe-Fe interatomic distances. The electronic properties of both compounds were investigated by means of DC Susceptibility, electrical resistivity and thermopower. U6Fe16Si7 is a Pauli paramagnet. Its electrical resistivity and thermopower point Out that it cannot be classified as a simple metal. The magnetic susceptibility Of U6Fe16Si7C is best described over the temperature range 100-300K by using a modified Curie-Weiss law with all effective magnetic moment of 2.3(2)mu(B)/U, a paramagnetic Weiss temperature, theta(p) = 57(2) K and a temperature-independent term chi(0) = 0.057(1)emu/mol. Both the electrical resistivity and thermopower reveal metallic behavior. (C) 2007 Elsevier Inc. All rights reserved.