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

Highlights: • 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. -- Abstract: 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