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Uranium-Induced Changes in Crystal-Field and Covalency Effects of Th4+ in Th1–xUxO2 Mixed Oxides Probed by High-Resolution X-ray Absorption Spectroscopy
Inorganic Chemistry ( IF 4.3 ) Pub Date : 2018-08-27 00:00:00 , DOI: 10.1021/acs.inorgchem.8b01142 Hongliang Bao 1 , Peiquan Duan 1, 2 , Jing Zhou 1 , Hanjie Cao 1, 2 , Jiong Li 1 , Haisheng Yu 1 , Zheng Jiang 1 , Hongtao Liu 1 , Linjuan Zhang 1 , Jian Lin 1 , Ning Chen 3 , Xiao Lin 1, 2 , Yancheng Liu 1 , Yuying Huang 1 , Jian-Qiang Wang 1
Inorganic Chemistry ( IF 4.3 ) Pub Date : 2018-08-27 00:00:00 , DOI: 10.1021/acs.inorgchem.8b01142 Hongliang Bao 1 , Peiquan Duan 1, 2 , Jing Zhou 1 , Hanjie Cao 1, 2 , Jiong Li 1 , Haisheng Yu 1 , Zheng Jiang 1 , Hongtao Liu 1 , Linjuan Zhang 1 , Jian Lin 1 , Ning Chen 3 , Xiao Lin 1, 2 , Yancheng Liu 1 , Yuying Huang 1 , Jian-Qiang Wang 1
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Knowledge of the local Th structure is a prerequisite for a better understanding of the physicochemical properties of the thorium-based mixed oxides (Th-MOX) involved in the Th-based nuclear fuel cycle. The crystalline electric field (CEF) splitting of the 6d shell in Th1–xUxO2 (x = 0.25, 0.5, 0.75) solid solution was probed by the Th L3 edge high-energy-resolution fluorescence-detected (HERFD) X-ray absorption near-edge spectroscopy (XANES) collected at the Lβ5 emission line, which cannot be obtained by conventional X-ray absorption methods. The detected CEF split between the 6d eg and t2g orbitals in ThO2 consisting of ordered Th–O8 cubes with cubic symmetry is ∼3.5 eV for the Th4+ ion. Because the split peaks of the white line corresponding to the crystal-field splitting of the unoccupied 6d states were resolved in the HERFD-XANES spectra, the analysis of these split peaks combined with first-principles calculations revealed that an increase of the U content involves the distortion of the Th–O8 cubes in the Th1–xUxO2 mixed oxides. The lower symmetry of the Th–O8 cube induced by the incorporated U tends to reduce the local crystal-field around Th4+ as well as the hybridization of Th 6t2g–O 2p which is mainly responsible for the covalent property of the Th–O bond. The phenomenon is noticeable in Th0.25U0.75O2, whose CEF splitting is decreased by approximately 10%, and covalent mixing between Th 6d t2g and O 2p orbitals is substantially reduced compared to that of pure ThO2.
中文翻译：
铀诱导的晶格变化和高分辨X射线吸收光谱探测的Th 1– x U x O 2混合氧化物中Th 4+的共价效应
了解局部Th结构是更好地了解参与Th基核燃料循环的based基混合氧化物（Th-MOX）的理化性质的前提。通过Th L 3边缘高能分辨荧光检测（HERFD ）探测6d壳在Th 1– x U x O 2（x = 0.25，0.5，0.75）固溶体中的结晶电场（CEF）分裂）X射线吸收近边光谱（XANES）在所收集的大号β5发射线，这是不能用传统的X射线吸收的方法获得。检测到的CEF在6d e g和t 2g之间划分对于Th 4+离子，由具有立方对称性的有序Th–O 8立方体组成的ThO 2中的轨道约为〜3.5 eV 。由于在HERFD-XANES光谱中解析了与未占据的6d态的晶体场分裂相对应的白线分裂峰，因此对这些分裂峰的分析与第一性原理的结合表明，U含量的增加涉及Th 1 – x U x O 2混合氧化物中Th–O 8立方体的变形。掺入的U引起的Th–O 8立方的较低对称性倾向于减小Th 4+周围的局部晶体场以及Th 6t 2g -O 2p的杂交，这主要是Th-O键的共价特性。这种现象在Th 0.25 U 0.75 O 2中很明显，其CEF分裂减少了约10％，与纯ThO 2相比，Th 6d t 2g和O 2p轨道之间的共价混合大大减少。
更新日期：2018-08-27
中文翻译：
铀诱导的晶格变化和高分辨X射线吸收光谱探测的Th 1– x U x O 2混合氧化物中Th 4+的共价效应
了解局部Th结构是更好地了解参与Th基核燃料循环的based基混合氧化物（Th-MOX）的理化性质的前提。通过Th L 3边缘高能分辨荧光检测（HERFD ）探测6d壳在Th 1– x U x O 2（x = 0.25，0.5，0.75）固溶体中的结晶电场（CEF）分裂）X射线吸收近边光谱（XANES）在所收集的大号β5发射线，这是不能用传统的X射线吸收的方法获得。检测到的CEF在6d e g和t 2g之间划分对于Th 4+离子，由具有立方对称性的有序Th–O 8立方体组成的ThO 2中的轨道约为〜3.5 eV 。由于在HERFD-XANES光谱中解析了与未占据的6d态的晶体场分裂相对应的白线分裂峰，因此对这些分裂峰的分析与第一性原理的结合表明，U含量的增加涉及Th 1 – x U x O 2混合氧化物中Th–O 8立方体的变形。掺入的U引起的Th–O 8立方的较低对称性倾向于减小Th 4+周围的局部晶体场以及Th 6t 2g -O 2p的杂交，这主要是Th-O键的共价特性。这种现象在Th 0.25 U 0.75 O 2中很明显，其CEF分裂减少了约10％，与纯ThO 2相比，Th 6d t 2g和O 2p轨道之间的共价混合大大减少。
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