Local and Electronic Structure of Americium‐Bearing PuO₂

Abstract

X‐ray diffraction and X‐ray absorption spectroscopy have shown that a material composed of two (Pu,Am)O2–x substoichiometric fluorite‐type structures is obtained by sintering in moisturized Ar/H2. The Pu oxidation state is strictly +IV, whereas Am exhibits a +III/+IV mixed valence. Thus, the Am–O system and particularly the Am oxidation state play a major role in the sintering behavior of the Pu–Am–O system. The heating of this compound in air leads to the formation of a fluorite Pu0.80Am0.20O1.98 solid solution. The transition from a one‐phase to a two‐phase structure takes place at a temperature lower than 800 °C. The results were compared with previous studies on Am‐bearing UO2 and ThO2, which have evidenced different behaviors.

The role of the 5f valence orbitals of early actinides in chemical bonding

“… 63 ) [UO 2 (H 2 O) 5 ](ClO 4 ) 2(cr) , NpO 2(am,hyd) , Ca 0.5 NpO 2 (OH) 2 ·1.3H 2 O, Na 2 Np 2 O 7(cr) (refs 64 , 65 ), NpO 2 2+ , PuO 2(cr) (ref. 66 ), Pu(III) (ref. 67 ), Pu(IV) and PuO 2 2+ were recorded by measuring HR-XANES spectra across a M α /M β normal emission line.…”

Melting behaviour of americium-doped uranium dioxide

“…The lattice parameter of the as-synthesized materials are also provided [5,40]. The data were measured at RT and at a pressure of (0.10 ± 0.01) MPa.…”

“…Fits were performed between 1.6 and 6 Å at both the U L II and Am L III edges, with a k-weight value of 3. As often employed for An L III /L II [18,[38][39][40], the amplitude factor (S 0 2 ) was set at 0.90 for U and Am shells. The shift in the threshold energy (DE 0 ) was varied as a global parameter.…”

Comparative XRPD and XAS study of the impact of the synthesis process on the electronic and structural environments of uranium–americium mixed oxides

“…In addition to the three single scattering paths (Me-O, Me-Me and Me-O), one multiple-scattering path (Me-OMe-O-Me) was also considered in the FEFF calculations. As often employed for An L III /L II [19][20][21][22][23][24][25], the amplitude factor (S 0 2 ) was set at 0.90 for U and Am shells. The shift in the threshold energy (ΔE 0 ) was varied as a global parameter.…”