The structural state of Finnish Cr- and V-bearing clinozoisite: insights from Raman spectroscopy
The structural state of Finnish Cr- and V-bearing clinozoisite: insights from Raman spectroscopy
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芬兰含铬和含钒斜帘石的结构状态：来自拉曼光谱的见解
DOI：
10.1007/s00269-020-01129-z
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发表时间：
2021
影响因子：
1.4
通讯作者：
Mihailova
中科院分区：
文献类型：
--
作者：
Nagashima;Armbruster T;Nishio-Hamate;Mihailova
Nagashima等人发现了来自芬兰Outokumpu铜矿的含Cr和V的斜生孢子（Czo）中的严重结构损伤（Eur J Miner 23：731-743，2011）。单晶X射线和电子衍射图案表明，中度到非常差的结构一致性，这表明在平移对称的故障的高密度。然而，由于放射性元素的浓度可以忽略不计，结晶度差不能归因于自辐射。将含Cr和V的C20退火至750 °C仅略微改善结晶度。为了解决这个谜，偏振拉曼光谱被应用于获得进一步的洞察到Cr + V轴承芬兰CZO的结构状态。根据富Cr + V（Czo-ts 3）、含Cr + V（Czo-ts 2）和不含Cr + V（Czo-ts 1）Czo的平行偏振拉曼光谱，峰随着Cr + V含量而变宽，表明结构缺陷密度增加。光谱从自形Cr + V轴承CZO单晶证据完整的结构域强极化和取向依赖性。因此，芬兰CZO的结构状态应被描述为具有共同的晶体取向的缺陷丰富的分段域。V和Cr的掺入强烈影响了3343 cm−1[（OH）a]和3435 cm−1[（OH）B]附近的拉曼活性O-H键伸缩模式，分别归属于O 10-H···O 4和O 10-H···O2氢桥。当Cr + V部分占据M3时，H···O2氢键被强烈促进，M2 O 6-链和（M1，M3）O 6-链之间的连接受到干扰，导致共格结构域的周期性缺陷和尺寸减小.在M_3Fe ~（3+）取代M_3Al的情况下，由较大的M_3位阳离子施加的局部应力在畸变的M_3O_6八面体内得到松弛。当M3 V ~（3+）或M3 Cr ~（3+）取代M3 Al时，M3 O ~ 6八面体的畸变较小，局部应力场传播的距离远于第一配位球，从而破坏了过渡对称性。新的高分辨率透射电子显微镜（HRTEM）图像确实显示了钙的纳米晶体。10 nm，具有由非晶区域包围的共同晶体取向。据建议，分割的大连贯的结晶区域中的Cr + V-丰富的CZO纳米晶体可能会触发一个潜在的兼容性差距结合缓慢的扩散行为的Cr 3+。此外，这项研究意味着，通常观察到的变形材料的纳米结构也可能是由应变效应和/或出溶现象排除缓慢扩散。
Severe structural damage in Cr- and V-bearing clinozoisite (Czo) from the Outokumpu copper mine, Finland, was discovered by Nagashima et al. (Eur J Miner 23:731–743, 2011). Single-crystal X-ray and electron diffraction patterns indicated moderate-to-very-poor structural coherency, suggesting a high density of faults in the translational symmetry. However, the poor crystallinity cannot be attributed to self-radiation due to negligible concentrations of radioactive elements. Annealing of Cr- and V-bearing Czo up to 750 °C only slightly improved crystallinity. To solve this enigma, polarized Raman spectroscopy was applied to gain further insights into the structural state of the Cr + V-bearing Finnish Czo. According to the parallel-polarized Raman spectra of Cr + V-rich (Czo-ts3), Cr + V-bearing (Czo-ts2), and Cr + V-free (Czo-ts1) Czo, the peaks broaden with the Cr + V content, indicating increasing density of structural defects. Spectra from a euhedral Cr + V-bearing Czo single-crystal evidence intact structural domains by strong polarization and orientation dependence. Thus, the structural state of Finnish Czo should be described in terms of defect-rich segmented domains with common crystallographic orientation. The incorporation of V and Cr into the clinozoisite structure strongly affects the Raman-active O–H bond stretching modes near 3343 cm−1[(OH)a] and 3435 cm−1[(OH)b], assigned to O10-H···O4 and O10-H···O2 hydrogen bridges, respectively. The H···O2 hydrogen bonding is strongly promoted when M3 is partially occupied by Cr + V, and as a result, the linkages between the M2O6- and (M1, M3)O6-chains are disturbed, leading to periodicity faults and size reduction of coherent structural domains. In the case ofM3Fe3+substitution forM3Al, the local stress imposed by the larger M3-site cation is relaxed within the distorted M3O6octahedron. In the case ofM3V3+orM3Cr3+substitution forM3Al, M3O6octahedra are less distorted and local stress fields propagate farther than only to the first coordination sphere, thus disturbing the transitional symmetry. New high-resolution transmission electron microscopy (HRTEM) images indeed display nanocrystals of ca. 10 nm with common crystallographic orientation surrounded by amorphous regions. It is suggested that the segmentation of large coherent crystalline areas in Cr + V-rich Czo to nanocrystals may be triggered by a potential miscibility gap in combination with the sluggish diffusion behavior of Cr3+. Moreover, this study implies that nanostructures as commonly observed for metamict materials may also be caused by strain effects and/or exsolution phenomena precluded by tardy diffusion.
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期刊：
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