Abstract
Both AmAlO3 and PuAlO3 perovskites have been synthesized and characterized using powder X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FT-IR), and 27Al magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR). AmAlO3 perovskite showed a rhombohedral configuration (space group R3̅c) in agreement with previous studies. The effect of americium α-decay on this material has been followed by XRD and 27Al 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 AmAlO3 perovskite was progressively converted into amorphous AmAlO3, with a total amorphization occurring after 8 months and 2 × 1018 α-decays/g. For the first time, PuAlO3 perovskite was synthesized with an orthorhombic configuration (space group Imma), showing an interesting parallel to CeAlO3 and PrAlO3 lanthanide analogues. High-temperature XRD was performed and showed a Imma → R3̅c phase transition occurring between 473 and 573 K. The thermal behavior of R3̅c PuAlO3 was followed from 573 to 1273 K, and extrapolation of the data suggests that cubic plutonium perovskite should become stable at around 1850 K (R3̅c → Pm3̅m transition).
Highlights
Space missions destined to cold, dark, and distant places in the solar system cannot rely on the sun to supply energy
X-ray diffraction (XRD) analysis showed ∼9% oxide is present with the americium perovskite after the synthesis
The analyses show a clear segregation of the 237Np impurity initially present in the americium within the oxide phase with a ratio between neptunium and americium (Np:Am) of ≈53:47
Summary
Space missions destined to cold, dark, and distant places in the solar system cannot rely on the sun to supply energy. LnAlO3 compounds mostly crystallize in three main perovskite structures, cubic Pm3̅m, rhombohedral R3̅c, and orthorhombic Pbnm (Figure 1) Transitions among these three phases depend on the radius of the lanthanide cation and the temperature. The CeAlO3 and PrAlO3 structures exhibit further tetragonal or monoclinic perovskite distortions, including the room-temperature phase of CeAlO3, which are not described here The formation of these low-temperature phases is surprising, because the neighboring compounds LaAlO3 and NdAlO3 keep rhombohedral configuration R3̅c at least down to 4.220 and 1 K,21 respectively. The study was extended to PuAlO3, because this material is relatively poorly described in the literature
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