Crystal and magnetic structure of the binary uranium germanide U3Ge5

The crystallographic structure of the binary uranium germanide U3Ge5 was de termined from single crystal X-ray diffraction data to R(F)=0.076 and R ome ga=0.085. U3Ge5 crystallizes with the hexagonal AlB2 structure type (P6/mmm ) with the following lattice parameters: a=3.954(1) Angstrom, c=4.125(1) An gstrom. A partial occupation of the germanium site leads to the effective c omposition UGe1.57 and the observation of weak superlattice reflections ind icates some ordering of the germanium vacancies which could not be resolved . Magnetic susceptibility measurements on an annealed polycrystalline sampl e revealed ferromagnetic ordering below T-c=94 K, which was previously clai med for the composition U3Ge4. The magnetic structure was determined from n eutron powder diffraction data collected on the G4-1 powder diffractometer at LLB Saclay. The structure is ferromagnetic (R-m=0.02) with the uranium m oments at 1.4 K: M-U=2.28(4) mu(B), described by a main component along the c-axis of the hexagonal subcell M-z=1.80(4) mu(B) and an in-plane componen t: M-x.y=1.40(5) mu(B). (C) 1999 Elsevier Science S.A. All rights reserved.