Crystal structure of moganite; a new structure type for silica
Crystal structure of moganite; a new structure type for silica
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DOI：
10.1127/ejm/4/4/0693
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发表时间：
1992-08
影响因子：
2.1
通讯作者：
G. Miehe;H. Graetsch
中科院分区：
文献类型：
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作者：
G. Miehe;H. Graetsch
利用透射电镜、扫描电镜、x射线粉末衍射、红外光谱和化学分析等手段对微晶二氧化硅矿物莫干石进行了结构表征，表明莫干石是一种与石英密切相关的新型AB 2结构类型。莫干石通常含有高达3 wt%的水，而水不是结构的组成部分。对x射线衍射数据进行Rietveld细化，得到剖面R值R=3.5%, R w =4.5%， GOF=8.0。Moganite基本为单斜晶，a=8.758(2), b=4.876(1), c=10.715(2) a, β=90.08(3)°，空间群I 12 /a 1， Z(sio2)=12， D=2.55 g cm #753。晶体经常显示出三斜的上层结构，使晶胞的体积增加一倍。晶体结构可以被认为是由交替的层组成——类似于（1011）——通过右旋和左旋石英切片——形成了一个共享角的sio4 -四面体的三维框架。因此，结构原理是根据巴西法在细胞尺寸尺度上的周期性孪生。当1/6的硅原子占据石英的4个位置时，石英结构的拓扑结构转变为莫干长石结构。除了6环和8环外，结构中还含有4环的sio4 -四面体
Structural characterization of the microcrystalline silica mineral moganite, using a combination of transmission and scanning electron microscopy, X-ray powder diffraction, infrared spectroscopy and chemical analyses, reveals that it represents a new AB 2 structure type which is closely related to quartz. Moganite typically contains up to 3 wt% of water which is not a constituent of the structure. Rietveld refinement of the X-ray diffraction data leads to profile R-values R=3.5%, R w =4.5%, GOF=8.0. Moganite is essentially monoclinic with a=8.758(2), b=4.876(1), c=10.715(2) A, β=90.08(3)°, space group I 1 2/a 1, Z(SiO 2 )=12, D=2.55 g cm #753 . The crystallites frequently display a triclinic superstructure which doubles the volume of the unit cell. The crystal structure can be thought of as consisting of alternating layers―resembling (1011)-slices through right- and left-handed quartz―which form a three dimensional framework of corner-sharing SiO 4 -tetrahedra. The structural principle is thus a periodic twinning according to the Brazil-law on a cell dimension scale. The topology of the quartz structure is transformed to the moganite topology if 1/6 of the Si-atoms occupies I 4 -positions of quartz. Besides the 6- and 8-rings, the structure contains 4-rings of SiO 4 -tetrahedra