CRYSTAL-STRUCTURE AND MAGNETIC-BEHAVIOR OF THE LAVES-TYPE PHASES U4MO5SI3 AND U4CR6SI2

U4Mo5Si3 and U4Cr6Si2 have been synthesized by argon arc-melting the e lemental combinations and annealing at 1400 degrees C. The homogeneity domains of U4Mo5+xSi3-x and U4Cr6+ySi2-y have been established by X-r ay powder and single-crystal diffraction analysis and range from x = 0 to 1 and from y = -0.5 to 1. Single-crystal X-ray studies have shown that the transition metal and the silicon are both distributed on the two sites occupied by zinc in the Laves phase MgZn2 (6h and 2a positio ns in P6(3)/mmc). Magnetic investigations of these compounds revealed temperature-independent paramagnetism as a result of the very short ur anium-uranium distance found in the structure determinations. (C) 1996 Academic Press, Inc.