Synthesis, Characterization, and Stability of Two Americium Vanadates, AmVO₃ and AmVO₄

In search for chemically stable americium compounds withhigh powerdensities for radioisotope sources for space applications, AmVO3 and AmVO4 were prepared by a solid-state reaction.We present here their crystal structure at room temperature solvedby powder X-ray diffraction combined with Rietveld refinement. Theirthermal and self-irradiation stabilities have been studied. The oxidationstates of americium were confirmed by the Am M-5 edge high-resolutionX-ray absorption near-edge structure (HR-XANES) technique. Such ceramicsare investigated as potential power sources for space applicationslike radioisotope thermoelectric generators, and they have to endureextreme conditions including vacuum, high or low temperatures, andinternal irradiation. Thus, their stability under self-irradiationand heat treatment in inert and oxidizing atmospheres was tested anddiscussed relative to other compounds with a high content of americium. AmVO3 and AmVO4 were prepared by asolid-state reaction and characterized in terms of crystal structure,americium and vanadium oxidation states, thermal behavior, and self-irradiationstability. With a fast amorphization behavior, large volume variation,and interchangeable structure as a function of the presence of theoxygen atmosphere and temperature, americium vanadates do not appearto be good candidates as Am forms for radioisotope power systems.