Notizen: Über Erdalkaliuranate (VI) und ihre Reduktionsprodukte

Nonstoichiometry in Strontium Uranium Oxide: Understanding the Rhombohedral–Orthorhombic Transition in SrUO4

“…Strontium is an important daughter of the fission of U for two reasons: first, it has a high fission yield in mixed oxide (MOX) fuels, and second, it is a major constituent of the “gray phase”, the multicomponent oxide precipitate that forms when MOX fuel is used to high burn-up. − SrUO 4 can be prepared in either a rhombohedral (α-SrUO 4 ) or orthorhombic (β-SrUO 4 ) structure depending on the synthesis conditions. − The transformation between the two forms occurs around 830 °C and is irreversible in air. , While not definitive, previous studies indicate that whereas β-SrUO 4 is stable and stoichiometric, α-SrUO 4 is metastable which can exist with oxygen deficiencies and is best described as α-SrUO 4−δ , ,− with the precise stoichiometry depending on the synthesis conditions.…”

“…10−13 The transformation between the two forms occurs around 830 °C and is irreversible in air. 14,15 While not definitive, previous studies indicate that whereas β-SrUO 4 is stable and stoichiometric, α-SrUO 4 is metastable which can exist with oxygen deficiencies and is best described as α-SrUO 4−δ , 11,15−18 with the precise stoichiometry depending on the synthesis conditions.…”

The role of π-bonding on the high temperature structure of the double perovskites Ba2CaUO6and BaSrCaUO6

“…The room temperature structure of the related oxide BaSrCaUO 6 has, to our knowledge, only been previously described once, by Kemmler-Sack and Seeman, 12 as cubic. Conversely Ba 2 CaUO 6 was first described by Rudorff and Pfitzer 13 as cubic, then as orthorhombic, 12 then as a slightly distorted cubic structure 14 and finally, more recently by Fu et al 15 as monoclinic in P2 1 /n. Given the paucity of contemporary studies of temperature induced phase transitions in uranium oxides, the current study seeks to increase our knowledge through an investigation of the high temperature behaviour of the two closely related oxides, Ba 2 CaUO 6 and BaSrCaUO 6 , using a combination of synchrotron X-ray and neutron diffraction.…”