Search for higher oxides of Pu: A photoemission study

After decades of believing in a very stable PuO2, suitable for final storage of nuclear waste, the existence of a higher oxide, PuO2+x, was recently claimed. This would have far reaching consequences on the strategies of storage of Pu-based waste. Its formation therefore has been discussed controversially for several years.In this work, existence and stability of the higher oxide, PuO2+x, has been probed by photoelectron spectroscopy study of PuO2 exposed to atomic oxygen. The validity of this approach is first tested on UO2, which oxidizes readily to UO3. Under the same reaction conditions, PuO2 is only covered by a chemisorbed layer of oxygen, which desorbs at elevated temperature. The study excludes the stability of any higher binary Pu oxide as a bulk species.