Crystal and magnetic structure of the binary uranium germanide U3Ge5

The crystallographic structure of the binary uranium germanide U3Ge5 was determined from single crystal X-ray diffraction data to R(F)=0.076 and R omega=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) Angstrom. A partial occupation of the germanium site leads to the effective composition UGe1.57 and the observation of weak superlattice reflections indicates some ordering of the germanium vacancies which could not be resolved. Magnetic susceptibility measurements on an annealed polycrystalline sample revealed ferromagnetic ordering below T-c=94 K, which was previously claimed for the composition U3Ge4. The magnetic structure was determined from neutron powder diffraction data collected on the G4-1 powder diffractometer at LLB Saclay. The structure is ferromagnetic (R-m=0.02) with the uranium moments 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 component: M-x.y=1.40(5) mu(B). (C) 1999 Elsevier Science S.A. All rights reserved.