Uranium–Americium oxides U_1−yAm_yO_2±x are promising candidates as possible transmutation targets for next generation nuclear reactors. In the context of a comprehensive investigation of their thermodynamic and thermal properties, the behaviour in oxidizing conditions is here studied. In a recent work, the behaviour in air of stoichiometric and sub-stoichiometric U_1−yAm_yO_2−x compounds, with various Am content, was investigated by high-temperature X-ray Diffraction. Herein, the hyper-stoichiometric oxides obtained from that study are investigated by X-ray Absorption Spectroscopy. The new data, together with the previous XRD results, allow determining the exact compositions of the samples and hence obtaining phase diagram points in the O-rich domain of the U-Am-O system. Indeed, five phase diagram points at 1473 K are obtained: two tie-lines in the M₄O₉-M₃O₈ domain, for Am/(Am + U) = 0.10 and 0.15, one tie line in the MO_2+x-M₃O₈ domain, for Am/(Am + U) = 0.28, and two points in the single phase MO_2±x domain, for higher americium concentration. From these data, it is also concluded that trivalent americium has a small solubility in the M₄O₉ and M₃O₈ phases.

铀-A氧化物U ₁ - _y Am _y O _{2± x}是有希望的候选物，可以作为下一代核反应堆的trans变目标。在对其热力学和热学性质进行全面研究的背景下，本文研究了在氧化条件下的行为。在最近的工作中，化学计量的和亚化学计量的U _{1− y} Am _y O _{2− x}在空气中的行为通过高温X射线衍射研究了具有不同Am含量的化合物。在此，通过X射线吸收光谱研究了从该研究获得的超化学计量的氧化物。新数据与先前的XRD结果一起，可以确定样品的确切组成，从而获得U-Am-O系统富O域中的相图点。实际上，在1473 K处获得了五个相图点：对于Am /（Am + U）= 0.10和0.15，M ₄ O ₉ -M ₃ O ₈域中的两条连接线，MO ₂₊中的一条连接线_x -M ₃ O ₈域，对于Am /（Am + U）= 0.28，并且在单相MO _2±中有两个点_x域，用于更高的a浓度。从这些数据还可以得出结论，三价a在M ₄ O ₉和M ₃ O ₈相中的溶解度较小。