In the majority of magnetic systems the surface is required to order at the same temperature as the bulk. In the present Letter, we report a distinct and unexpected surface magnetic phase transition at a lower temperature than the Néel temperature. Employing grazing incidence x-ray resonant magnetic scattering, we have observed the near-surface behavior of uranium dioxide. UO2 is a noncollinear...

Jeongmook Lee a , Jandee Kim a , Young-Sang Youn a , Jong-Goo Kim a , Yeong-Keong Ha a and Jong-Yun Kim a,b * a Nuclear Chemistry Research Division, Korea Atomic Energy Research Institute, 989-111 Daedeok-daero, Yuseong-gu, Daejeon, 34057, Republic of Korea b Radiochemistry & Nuclear Nonproliferation, University of Science & Technology, Gajeong-ro 217, Yuseong-gu, Daejeon, 34113, Republic of Ko...

In 2004, as many as 444 nuclear energy reactors were operated in 31 countries worldwide. Most of them burn classical nuclear fuels, thus either uranium dioxide UO2 containing natural uranium, uranium enriched by U-235 or, less often, the so-called MOX (Mixed Oxide) fuel, which is a mixture of UO2 and PuO2 . The use of nuclear fuels and introduction of their novel types requires detailed knowled...

The electrochemical reduction of H2O2 on SIMFUEL was investigated over the pH range 1 to 4. The mechanism at pH 4 is known to occur on U species incorporated into a surface layer of U1-2xU2xO2+x. However, below pH 3, reduction occurs on an adsorbed UO2(OH) state which is unstable and oxidizes to insulating U before dissolving as UO2. Both schemes are observed at intermediate pH’s. The presence ...

Penta-ammine dioxide uranium(V) nitrate ammonia (1/1), [UO2(NH3)5]NO3·NH3, was obtained in the form of yellow crystals from the reaction of caesium uranyl nitrate, Cs[UO2(NO3)3], and uranium tetra-fluoride, UF4, in dry liquid ammonia. The [UO2]+ cation is coordinated by five ammine ligands. The resulting [UO2(NH3)5] coordination polyhedron is best described as a penta-gonal bipyramid with the O...