CRYSTAL-STRUCTURE AND MAGNETIC-PROPERTIES OF THE DIURANIUM TRITELLURIDE U2TE3

Single crystals of U2Te3 were obtained by solid state reaction between the elements in stoichiometric proportions mixed with a small quantit y of cesium chloride. U2Te3 crystallizes in the orthorhombic system, s pace group Pnma (n degrees 62), with unit cell parameters a = 12.175(2 )Angstrom, b = 4.370(1)Angstrom, c = 11.828(2)Angstrom, and Z = 4. The structure was determined from single crystal X-ray diffraction data a nd refined to final residual factors R(F) = 0.030 and R omega(F) = 0.0 35 for 32 variable parameters and a unique data set of 1100 diffractio n intensities [I > 3 sigma(I)]. The U atoms are located on two 4c non equivalent crystallographic positions. U(1) has a 7-fold coordination of Te atoms with a coordination polyhedron deriving from an octahedron in which one apex is split into two positions, and U(2) has a monocap ped trigonal prismatic coordination. U2Te3 exhibits rather complex mag netic behaviour, with an onset of ferromagnetic order at T similar to 110 K and spin reorientation below 105 K.