Tilting and Distortion in Rutile-Related Mixed Metal Ternary Uranium Oxides: A Structural, Spectroscopic, and Theoretical Investigation.
Tilting and Distortion in Rutile-Related Mixed Metal Ternary Uranium Oxides: A Structural, Spectroscopic, and Theoretical Investigation.
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金红石相关混合金属三元铀氧化物的倾斜和变形：结构、光谱和理论研究。
DOI：
10.1021/acs.inorgchem.0c03077
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发表时间：
2021
影响因子：
4.6
通讯作者：
B. Kennedy
中科院分区：
文献类型：
--
作者：
Gabriel L. Murphy;Zhaoming Zhang;Rebekka Tesch;P. Kowalski;M. Avdeev;E. Kuo;D. Gregg;P. Kegler;E. Alekseev;B. Kennedy
采用高分辨结构和光谱测量相结合的方法，在从头计算的支持下，系统地研究了金红石相关的三元铀AuO4氧化物结构扭曲的原因。用中子粉末衍射和同步辐射X射线粉末衍射或单晶X射线衍射相结合的方法，高精度地测定了β-CdUO4、MnUO4、CoUO4和MgUO4的结构。β-CdUO4的结构由Cmmm空间群描述得最好，而MnUO4、CoUO4和MgUO4由较低对称性的IBMM空间群描述，并且与先前报道的β-NiUO4同构[Murphy et al.Inorg.化学。2018年，57,13847]。X射线吸收光谱(XAS)分析表明，所有五种氧化物都含有六价铀。空间群的差异可以根据A2+和U6+阳离子之间的尺寸失配来理解，由此不令人满意的匹配导致结构扭曲，表现为AO6多面体的倾斜，导致对称性从Cmmm变为Ibmm。这种倾斜在CMMM结构中是不存在的。加热IBMM AUO4氧化物导致倾斜角减小。对于MnUO4，现场S-X射线衍射测量显示在T=200°C附近发生了向Cmmm的二级相变，基于现场变温S-X射线衍射数据的外推，预测CoUO4在DFT1475°C将经历向Cmmm的连续相变。通过测量数据与计算数据的比较，突出了∼+U方法的不足，所进行的分析将指导未来计算方法的改进。这项调查的结果是在更广泛的AUO4氧化物家族的背景下讨论的。
A systematic investigation examining the origins of structural distortions in rutile-related ternary uranium AUO4 oxides using a combination of high-resolution structural and spectroscopic measurements supported by ab initio calculations is presented. The structures of β-CdUO4, MnUO4, CoUO4, and MgUO4 are determined at high precision by using a combination of neutron powder diffraction (NPD) and synchrotron X-ray powder diffraction (S-XRD) or single crystal X-ray diffraction. The structure of β-CdUO4 is best described by space group Cmmm whereas MnUO4, CoUO4, and MgUO4 are described by the lower symmetry Ibmm space group and are isostructural with the previously reported β-NiUO4 [Murphy et al. Inorg. Chem. 2018, 57, 13847]. X-ray absorption spectroscopy (XAS) analysis shows all five oxides contain hexavalent uranium. The difference in space group can be understood on the basis of size mismatch between the A2+ and U6+ cations whereby unsatisfactory matching results in structural distortions manifested through tilting of the AO6 polyhedra, leading to a change in symmetry from Cmmm to Ibmm. Such tilts are absent in the Cmmm structure. Heating the Ibmm AUO4 oxides results in reduction of the tilt angle. This is demonstrated for MnUO4 where in situ S-XRD measurements reveal a second-order phase transition to Cmmm near T = 200 °C. Based on the extrapolation of variable temperature in situ S-XRD data, CoUO4 is predicted to undergo a continuous phase transition to Cmmm at ∼1475 °C. Comparison of the measured and computed data highlights inadequacies in the DFT+U approach, and the conducted analysis should guide future improvements in computational methods. The results of this investigation are discussed in the context of the wider AUO4 family of oxides.