Uranium oxide crystal structure

The crystal structures of a number of diphosphine disulphides (121) and (122) show a remarkable constancy in the bond lengths. Two types of molecule are observed in the crystal of the tetramethyl compound (121, X = Y = Me). The crystal structure of triphenylphosphine oxide (P—C 176 pm, P—O 164 pm) varies little from that observed in the uranium oxide complexes, and does not confirm P—O bond lengthening in complexes, as indicated by vp=.o (see Section 3C). 

Uranium oxides are of importance in the nuclear industry, and for this reason considerable effort has been put into understanding their nonstoichiometric behavior. The dioxide, U02 crystallizes with the fluorite structure with an ideal composition MX2 (Fig. 4.7a) but is readily prepared in an oxygen-rich form. In this state it is... 

Boussie, T.R., Eisenberg, D.C., Rigsbee, J. et al. (1991) Structures of organo-f-element compounds differing in the oxidation state of the central metal crystal structures of bis([8]annulene) complexes of cerium(lV), ytterbium(III), and uranium(III). Organometallics, 10, 1922. 

A representative crystal structure of with two triphenylphosphine oxide molecules and four bromide ions is shown in Figure 15. Coordination of the triphenylphosphine oxide ligands occurs via the oxygen of the P=0 group in trans positions. The bromide atoms coordinate equatorially, making the uranium six-coordinate with an octahedral geometry. ... 

Uranium dioxide has a number of properties that make it suitable for a fuel. The crystal structure is the fluorite (CaF2) type, similar to that of calcia-stabilised zirconia, and is stable to temperatures in excess of 2000 °C. Because it is a ceramic oxide, the material is refractory, chemically inert and resistant to corrosion Enrichment does not change these features. The oxide powder is pressed into pellets and sintered to a density of about 95 % maximum by traditional ceramic processing technology but is carried out in conditions that minimise risks from radiation effects. The pellets are contained in zirconium alloy (zircaloy) containers, which are then introduced into the reactor. The moderator, which... 

A suitable fuel, used in the Galileo Jupiter explorer, which was finally destroyed in 2003, is the isotope Pu. This is an a-emitter, which provides about 0.5 Wg . The half-life is 87.4 years. The fuel is the solid oxide plutonium dioxide, Pu02. Chemically, it is similar to the uranium dioxide used in thermal reactors, and adopts the same fluorite (Cap2) crystal structure, similar to that of calcia-stabiUsed zirconia and UO2. This structure is inert chemically and stable up to the melting point of approximately 2500 °C. The oxide is pressed and sintered into pellets under conditions that lead to high density and low, but not zero, porosity. This is to ensure dimensional stability of the pellets over the lifetime of the spacecraft because, as Pu is an a-emitter, the resulting helium gas must be allowed to escape. 

Samarskite-(Y) is a complex oxide of rare earths, uranium, calcium, niobium, tantalum and other elements it always occurs in the metamict state. This characteristic has been an obstruction to the study of the chemistry and crystal structure of this mineral. Although many chemical formulae and crystallographic data for samar-skite-(Y) have been proposed, no complete chemical or structural understanding of samarskite-(Y) has been achieved. 

Lead is a member of Group IVB of the periodic table with two oxidation states (Pb and Pb ), but the chemistry of the element is dominated by Pb ion. Lead has four isotopes with three of them being the tdtimate decay products of uranium and and, therefore, widely used in geological dating. The crystal structure of lead in solid form is face-centered cubic (FCC) with a lattice parameter of 4.95 A at 20°C. Lead is a blue-gray metal with density (11.3 g/cm ) 50 % more than that of steel and four times that of aluminum. However, lead is malleable, soft, and melts at only 327°C, and therefore, readily cut and shaped into pipes and sheets since ancient times. 

Kovba L. M. Crystal structure of potassium uranium oxide K2U7O22. Zh. strukt. khim., 13, 1972, 256-9. 

Brthet, J. C., Thuery, R, and Ephritikhine, M. 2005. Unprecedented reduction of the uranyl ion [U02] + into a polyoxo uranium(IV) cluster Synthesis and crystal structure of the first f-element oxide with a M6( i3-0)8 core. Chem. Commun. 3415-3417. 

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