Structure of UC2 and U2C3:XRD, 13C NMR and EXAFS study

• A structural investigation of UC2 and U2C3 phases was made with XRD, NMR and EXAFS.
• Heat treatment of a pulverised UC2 ingot, repressed into a pellet yields a U2C3 phase coexisting with UC2−z.
• Heat treatment of UC2 as cast ingots results in a partial decomposition to UC.
• EXAFS data confirmed the CaC2 and Pu2C3 type structure for UC2 and U2C3 respectively.
• 13C MAS NMR identified a contribution of a well and less ordered phases in UC2.

In this study, uranium dicarbide (UC2) has been prepared by arc melting and heat treated under vacuum to form uranium sequicarbide (U2C3) in the presence of a second phase UC2−z. Both samples, as cast and heat treated, have been characterised by chemical analyses, X-ray diffraction (XRD), 13C magic angle spinning nuclear magnetic resonance (MAS-NMR) and by extended X-ray absorption fine structure (EXAFS). The composition, the purity, the various environments of both U and C atoms as well as the bonds length with the coordination number have been determined. By combining a long-range order method (XRD) and short-range order spectroscopy techniques (EXAFS and NMR), a unique view on the microstructure of UC2, before and after heat treatment, and of U2C3 phase has been achieved.