b'Figure 1. Visualization of the refinedfurnace at temperatures up to along the crystallographic c-axis crystal structure of U 3 Si 2.00(a)1150 C (S. Vogel/LANL). Thethan along the a-axis for one of and U 3 Si 2.01(b) samples includingneutron diffraction data wasthe two uranium sites while the anisotropic atomic displacement parameters at ambient temperature.analyzed using the Rietveld methodsecond uranium site and the silicon Overlaid with the crystal structure areby T. Ulrich (University of Southatom showed an approximately the difference Fourier maps for ~60%Carolina, Columbia) and S. Vogelspherical atomic displacement of the maximum density (yellow positive(LANL). The neutron diffractionat all temperatures investigated. difference, blue negative difference). The uranium atoms are shown in grey,data analysis provided latticeFrom the unit cell and atom with U1 on the corners of the tetragonalparameters of the tetragonal unitposition parameters, the bond unit cell, while Si atoms are shown incell, atom positions of the uraniumlengths could be computed as a blue. The identified 4e site for excess Siand silicon atoms, and anisotropicfunction of temperature. The bond atoms is between the U1 atoms.atomic displacement parameters as alength allowed to compute strains, function of temperature. Significantidentifying stronger and weaker differences in volume expansionbonds within the unit cell. At no as well as thermal expansion alongtemperature were any additional the a and c-axes were found for thephases observed. The analysis of two compounds. The anisotropicthe difference Fourier map from atomic displacement parametersthe high-quality ambient condition showed an approximately fiveruns revealed scattering density not times larger thermal motionaccounted for in the stoichiometric 48 2019|AFC ACCOMPLISHMENTS'