Aliovalent Cation Substitution in UO2: Electronic and Local Structures of U1–yLayO2±x Solid Solutions,Inorganic Chemistry

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Aliovalent Cation Substitution in UO2: Electronic and Local Structures of U1–yLayO2±x Solid Solutions
Inorganic Chemistry ( IF 4.3 ) Pub Date : 2018-01-12 00:00:00 , DOI: 10.1021/acs.inorgchem.7b02839
Damien Prieur _{1,

2,

3} , Laura Martel ₁ , Jean-François Vigier ₁ , Andreas C. Scheinost _{2,

3} , Kristina O. Kvashnina _{2,

3} , Joseph Somers ₁ , Philippe M. Martin ₄

Affiliation

For nuclear fuel related applications, the oxygen stoichiometry of mixed oxides U_1–yM_yO_2±x is an essential property as it affects fuel properties and may endanger the safe operation of nuclear reactors. A careful review of the open literature indicates that this parameter is difficult to assess properly and that the nature of the defects, i.e., oxygen vacancies or U^V, in aliovalent cation–doped UO₂ is still subject to controversy. To confirm the formation of U^V, we have investigated the room-temperature stable U_1–yLa_yO_2±x phase using several experimental methods (e.g., XRD, XANES, and NMR) confirmed by theoretical calculations. This paper presents the experimental proof of U^V and its effect we identified in both electronic and local structure. We observe that U^V is formed in quasi-equimolar proportion as La^III in U_1–yLa_yO_2±x (y = 0.06, 0.11, and 0.22) solid solutions. The fluorite structure is maintained despite the cationic substitution, but the local structure is affected as variations of the interatomic distances are found. Therefore, we provide here the definitive proof that the substitution of U^IV with La^III is not accommodated by the creation of O vacancies as has often been assumed. The UO₂ fluorite structure compensates the incorporation of an aliovalent cation by the formation of U^V in quasi-equimolar proportions.

中文翻译：

UO _2中的铝价阳离子取代：U _{1 – y} La _y O _{2± x}固溶体的电子和局部结构

对于与核燃料有关的应用，混合氧化物U _{1- y} M _y O _{2± x}的氧化学计量是必不可少的属性，因为它会影响燃料属性并可能危及核反应堆的安全运行。对开放文献的仔细审查表明，该参数难以正确评估，并且在掺杂有金属价阳离子的UO ₂中的缺陷性质（例如，氧空位或U ^V）仍存在争议。为了确认U ^V的形成，我们研究了室温下稳定的U ₁_{– y} La _y O _2±_x理论计算证实了使用几种实验方法（例如XRD，XANES和NMR）检测液相的可行性。本文介绍了U ^V的实验证明及其在电子和局部结构中的作用。我们观察到，在U _1-_y La _y O _2±_x（y = 0.06、0.11和0.22）固溶体中，U ^V以准等摩尔比例形成为La ^III。尽管有阳离子取代，但萤石结构仍保持不变，但随着发现原子间距离的变化，局部结构会受到影响。因此，我们在这里提供了确定的证据，证明了用La代替U ^IV经常假设O职位空缺无法容纳^III。UO ₂萤石结构通过形成准等摩尔比例的U ^V补偿了铝价阳离子的掺入。

更新日期：2018-01-12

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