Uranium dioxide (UO₂) is a widely studied material due to its use as fuel in pressurised water reactors (PWR), and Raman spectroscopy is a technique of choice to characterise the evolution of its microstructure. UO₂ crystallises in a fluorite CaF₂ (space group Fm-3m) structure that gives rise to a unique Raman signature, the T_2g band. However, several other bands are often detected whose attribution remains unclear. The present study gives new insights on the Raman spectrum of UO₂ thanks to the combination of isotopic labelling with ¹⁸O and Raman imaging. In addition to the expected T_2g, U₂ (LO), 2LO and U₃ bands, we have detected a doublet at 885 and 925 cm⁻¹, a U* band at 555 cm⁻¹ in some specific areas and two bands located at 367 and 1196 cm⁻¹. All Raman bands shift under the effect of the replacement of ¹⁶O by ¹⁸O, excepting for the U* band that could not be detected anymore. The isotopic shift ratio could be determined for 20% and 30% ¹⁸O labelling. No discrepancy in band position is observed between grains and grain boundaries, except for the U₂(LO) band. We also evidence a difference between the U defect bands and the 885 and 925 cm⁻¹ doublet bands evolution under labelling, although the latter also seems to be connected to the presence of defects in the material.

中文翻译：

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氧同位素对多晶二氧化铀 UO2 拉曼图的影响

二氧化铀 (UO ₂ ) 由于在压水堆 (PWR) 中用作燃料而成为一种被广泛研究的材料，而拉曼光谱是表征其微观结构演变的一种技术。 UO ₂在萤石 CaF ₂（空间群 Fm-3m）结构中结晶，产生独特的拉曼特征，即 T _2g带。然而，经常检测到其他几个条带，其归属仍不清楚。由于同位素标记与¹⁸ O 和拉曼成像的结合，本研究对 UO ₂的拉曼光谱提供了新的见解。除了预期的 T _2g、U ₂ (LO)、2LO 和 U _{3带外，我们还在 885 和 925 cm} ^-1处检测到了双峰，在一些特定区域中在 555 cm ^-1处检测到了U* 带，并且位于在367和1196 cm ^-1。所有拉曼谱带在¹⁶ O 被¹⁸ O取代的影响下都会发生偏移，除了无法再检测到的 U* 谱带外。可以确定 20% 和 30% ¹⁸ O 标记的同位素位移比。除 U ₂ (LO) 能带外，在晶粒和晶界之间没有观察到能带位置的差异。我们还证明了 U 缺陷带与标记下的 885 和 925 cm ^-1双峰带演化之间的差异，尽管后者似乎也与材料中缺陷的存在有关。