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Neutron diffraction study of thermal parameters in U X 3 compounds

1981; International Union of Crystallography; Volume: 37; Issue: 4 Linguagem: Inglês

10.1107/s0567739481001289

1600-8596

J. Faber, G. H. Lander, P. J. Brown, A. Delapalme,

Thermodynamic and Structural Properties of Metals and Alloys

The intensities of the weak superlattice reflections in the UX3 compounds, where X = Ru, Rh, Ge, and Sn, have been measured by neutron diffraction. These compounds have the ordered AuCu3 structure. Excellent fits to the observed intensities are obtained by introducing anisotropic second-order and fourth-order (anharmonic) terms to describe the probability distribution function at the X atom site. The ratio of the magnitude of the mean-square thermal vibration parallel to and perpendicular to the unique tetragonal axis of the X atom appears to depend on whether p bonding (UGe3, USn3) or d bonding (URu3, URh3) occurs with the U electrons. In UGe3 data out to Q = 13 Å-1 show the need to include a fourth-order anharmonic term. The form of this anharmonicity suggests an attractive potential between the nearest- neighbor U-X atoms.