XPS-AES characterization of plutonium oxides and oxide carbide. The existence of plutonium monoxide

The plutonium-oxygen phase diagrams has been clarified by XPS and AES results which show that three oxygen-containing plutonium phases, PuO/sub 2/, ..cap alpha..-Pu/sub 2/O/sub 3/, and PuO/sub x/C/sub y/, are successively formed when oxide-coated plutonium metal is heated in vacuo to 500/sup 0/C. Formation of the oxide carbide is evidenced by the fact that a shift in the Pu(4f/sub 7/2/) binding energy is coincident with changes in the C(1s) photoelectron and C(KLL) Auger spectra, showing that unbound carbon is converted to carbide. The reaction conditions duplicate those at which plutonium monoxide reportedly forms and demonstrate that the NaCl-type surface phase previously identified as PuO is actually PuO/sub x/C/sub y/. The oxide carbide has a spectroscopically determined composition of PuO/sub 0.65+-0.15/C/sub 0.45+-0.15/ and reacts with CO, CO/sub 2/, and O/sub 2/ at low pressures to form PuO/sub 2/ and unbound carbon in a coherent product layer (approx. 20 nm thick) which retards further oxidation. Estimated thermodynamic data for PuO/sub x/C/sub y/ are consistent with the observed formation and oxidation reactions. The Pu(4f/sub 7/2/) binding energies for PuO/sub 2/, ..cap alpha..-Pu/sub 2/O/sub 3/, PuO/sub x/C/sub y/, and Pu are 426.1, 424.4, 423.6, and 422.2 eV, respectively.