High-Pressure Synthesis, Structural, and Spectroscopic Studies of the Ni-U-O System.
High-Pressure Synthesis, Structural, and Spectroscopic Studies of the Ni-U-O System.
复制标题
Ni-U-O 体系的高压合成、结构和光谱研究。
DOI：
10.1021/acs.inorgchem.8b02355
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发表时间：
2018
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;P. Kegler;Yingjie Zhang;Zhaoming Zhang;E. Alekseev;M. D. de Jonge;B. Kennedy
首次报道了 Ni-U-O 系统的全面结构研究。合成了 α-NiUO4、β-NiUO4 和 NiU3O10 的单晶，并利用 X 射线吸收光谱测量支持的同步加速器单晶 X 射线衍射数据对它们的结构进行了精修。 α-NiUO4 在 Pbcn 空间群中采用斜方结构，与 CrUO4 具有同构结构，在 [001] 方向上包含共享角的 UO6 多面体的波纹二维 (2D) 层和共享边的一维 (1D) 锯齿形 α-PbO2 金红石状 NiO6 多面体链。 β-NiUO4 与 MgUO4 具有同构结构，并且在 Ibmm 空间群中具有斜方结构，与常规 TiO2 金红石一样，其在 [001] 方向上包含共边 UO6 和 NiO6 多面体的交替一维链。 NiU3O10 在空间群 P1̅ 中形成三斜结构，并且与 CuU3O10 具有同构结构，其中它形成通过 UO6 和 UO7 多面体的混合物构建的三维 (3D) 框架结构，其中 NiO6 多面体孤立地位于框架内。使用单晶 XANES 测绘进行的 X 射线吸收近边缘结构 (XANES) 测量支持这三种结构中存在六价铀。研究发现 NiUO4 的多晶型物仅在高压和高温条件下（≥4 GPa 和 700 °C）形成。有人认为，这是 Ni2+ 和 U6+ 阳离子之间相对尺寸差异的结果，其中 Ni2+ 阳离子对于 Ibmm 结构来说实际上太小，而对于 Pbcn 结构来说太大，无法在环境压力条件下形成。这对于 NiU3O10 来说似乎不是问题，它是在环境压力条件下形成的，其中 NiO6 多面体在 3D 连接的 UO6/UO7 多面体的框架内孤立存在。合成条件表明，β-NiUO4 是优选的高压相，并且当 P = 4 GPa 时，在 950 至 1000 °C 之间的温度下发生不可逆的转变。氧化物的合成路线以及相关的结构和光谱结果根据 Ni-U-O 系统的结构化学、较大的 AUO4 族氧化物（A = 二价或三价阳离子）以及它们与金红石相关氧化物族的关系进行了描述。
The first comprehensive structural study of the Ni-U-O system is reported. Single crystals of α-NiUO4, β-NiUO4, and NiU3O10 were synthesized, and their structures were refined-using synchrotron single-crystal X-ray diffraction data supported by X-ray absorption spectroscopic measurements. α-NiUO4 adopts an orthorhombic structure in space group Pbcn and is isostructural to CrUO4 containing corrugated two-dimensional (2D) layers of corner-sharing UO6 polyhedra and edge-sharing one-dimensional (1D) zigzag α-PbO2 rutile-like chains of NiO6 polyhedra in the [001] direction. β-NiUO4 is isostructural to MgUO4 and has an orthorhombic structure in space group Ibmm, which contains alternating 1D chains of edge-sharing UO6 and NiO6 polyhedra in the [001] direction as in regular TiO2 rutile. NiU3O10 forms a triclinic structure in space group P1̅ and is isostructural with CuU3O10, where it forms a three-dimensional (3D) framework structure built through a mixture of UO6 and UO7 polyhedra in which the NiO6 polyhedra sit isolated within the framework. X-ray absorption near-edge structure (XANES) measurements, conducted using XANES mapping of single crystals, support the presence of hexavalent uranium in the three structures. The polymorphs of NiUO4 were found to only form under high-pressure and high-temperature conditions (≥4 GPa and 700 °C). It is argued that this is a consequence of the relative size difference between the Ni2+ and U6+ cations, where the Ni2+ cation is effectively too small for the Ibmm structure and too large for the Pbcn structure to form under ambient pressure conditions. This does not appear to be an issue for NiU3O10, which forms under ambient pressure conditions, where NiO6 polyhedra sit isolated within the framework of 3D connected UO6/UO7 polyhedra. Synthesis conditions indicate that β-NiUO4 is the preferred higher-pressure phase and that the transformation to this occurs irreversibly at a temperature between 950 and 1000 °C, when P = 4 GPa. The routes toward the synthesis of the oxides and the associated structural and spectroscopic results are described with respect to the structural chemistry of the Ni-U-O system, the larger AUO4 family of oxides (A = divalent or trivalent cation), and also their relation to the rutile-related family of oxides.