Charge distribution and local structure of americium-bearing thorium oxide solid solutions.

The electronical and structural properties of Th0.80Am0.20O2–x materials have been studied by the coupling of X-ray diffraction and X-ray absorption spectroscopy techniques. A substoichiometric fluorite ThIV0.80AmIII0.20O1.90 solid solution is found following sintering in moisturized Ar–H2. In contrast, heating of this sample in air leads to a nondefective fluorite ThIV0.80AmIV0.20O2.00 solid solution. The structures of these solid solution compounds were fully characterized by assessing the interatomic distances, the coordination numbers, and the structural disorder. The effect of the sintering atmosphere on these crystallographical parameters and on the cation valences has been determined and the capability of ThO2 to accommodate tri- and tetravalent actinides in the fluorite structure assessed.