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 M2O 6 - and (M1, M3)O 6 -chains are disturbed, leading to periodicity faults and size reduction of coherent structural domains. In the case of M3 Fe 3+ substitution for M3 Al, the local stress imposed by the larger M3-site cation is relaxed within the distorted M3O 6 octahedron. In the case of M3 V 3+ or M3 Cr 3+ substitution for M3 Al, M3O 6 octahedra 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 Cr 3+ . 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.

中文翻译：

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芬兰含 Cr 和 V 的斜长岩的结构状态：来自拉曼光谱的见解

Nagashima 等人发现来自芬兰奥托昆普铜矿的含铬和钒的斜纹岩 (Czo) 存在严重的结构损伤。(Eur J Miner 23:731–743, 2011)。单晶 X 射线和电子衍射图显示中度至极差的结构相干性，表明平移对称性中存在高密度的断层。然而，由于放射性元素的浓度可忽略不计，结晶度差不能归因于自辐射。含 Cr 和 V 的 Czo 退火至 750 °C 仅略微改善结晶度。为了解决这个谜团，应用偏振拉曼光谱来进一步了解含 Cr + V 的芬兰 Czo 的结构状态。根据 Cr + V-rich (Czo-ts3)、Cr + V-bearing (Czo-ts2) 和 Cr + V-free (Czo-ts1) Czo 的平行偏振拉曼光谱，峰随着 Cr + V 含量的增加而变宽，表明结构缺陷的密度增加。来自自形 Cr + V 的 Czo 单晶的光谱通过强极化和取向依赖性证明完整的结构域。因此，芬兰 Czo 的结构状态应该用具有共同晶体取向的富含缺陷的分段域来描述。V 和 Cr 掺入斜长石结构强烈影响拉曼活性 O-H 键拉伸模式附近 3343 cm -1 [(OH)a] 和 3435 cm -1 [(OH)b]，分配给 O10-H ···O4 和 O10-H···O2 分别形成氢桥。当 M3 部分被 Cr + V 占据时，H...O2 氢键被强烈促进，结果，M2O 6 - 和 (M1, M3)O 6 - 链之间的键被扰乱，导致周期性故障和相干结构域的尺寸减小。在 M3 Fe 3+ 替代 M3 Al 的情况下，较大的 M3 位阳离子施加的局部应力在扭曲的 M3O 6 八面体内松弛。在 M3 V 3+ 或 M3 Cr 3+ 替代 M3 Al 的情况下，M3O 6 八面体扭曲较小，局部应力场传播得比仅第一配位球更远，从而扰乱了过渡对称性。新的高分辨率透射电子显微镜 (HRTEM) 图像确实显示了约 10 nm 具有共同的晶体取向，周围环绕着非晶区。建议将富含 Cr + V 的 Czo 中的大相干晶体区域分割为纳米晶体可能是由潜在的混溶间隙与 Cr 3+ 的缓慢扩散行为相结合引发的。