Temperature-dependent crystal structure of U3Si2 by high-temperature neutron diffraction

The crystal structure of the U₃Si₂ line compound in the U-Si system was investigated as a function of temperature from room temperature to 1373 K using high temperature neutron time-of-flight diffraction on the High-pressure Pressure/preferred Preferred Orientation (HIPPO) diffractometer at the Los Alamos Neutron Science Center (LANSCE). The U-Si system is actively researched due to its promise as an accident tolerant nuclear fuel. The simultaneous Rietveld refinement of five histograms from the five HIPPO detector rings provided fundamental datasets for the lattice parameters, anisotropic atomic displacement parameters, and atomic positions as a function of temperature. To explore the possibility of a homogeneity range, two samples were analyzed, stoichiometric U₃Si_2.00 and a hyperstoichiometric U₃Si_2.01. While minor differences in the thermal expansion anisotropic atomic displacement parameters between the two samples were observed, over the entire investigated temperature range no additional phases were observed. However, significant differences in the thermal expansion behavior were identified between the two compositions that warrant future investigations.