Plutonium and Americium Aluminate Perovskites.

Both AmAlO ₃ and PuAlO ₃ perovskites have been synthesized and characterized using powder X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FT-IR), and ²⁷ Al magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR). AmAlO ₃ perovskite showed a rhombohedral configuration (space group R 3̅ c ) in agreement with previous studies. The effect of americium α-decay on this material has been followed by XRD and ²⁷ Al MAS NMR analyses. In a first step, a progressive increase in the level of disorder in the crystalline phase was detected, associated with a significant crystallographic swelling of the material. In a second step, the crystalline AmAlO ₃ perovskite was progressively converted into amorphous AmAlO ₃ , with a total amorphization occurring after 8 months and 2 × 10 ¹⁸ α-decays/g. For the first time, PuAlO ₃ perovskite was synthesized with an orthorhombic configuration (space group Imma ), showing an interesting parallel to CeAlO ₃ and PrAlO ₃ lanthanide analogues. High-temperature XRD was performed and showed a Imma → R 3̅ c phase transition occurring between 473 and 573 K. The thermal behavior of R 3̅ c PuAlO ₃ was followed from 573 to 1273 K, and extrapolation of the data suggests that cubic plutonium perovskite should become stable at around 1850 K ( R 3̅ c → Pm 3̅ m transition).