X-ray diffraction and niolecular dynamics studies of the phase transitions in selica clathrote miuerals

Selica 笼形分子相变的 X 射线衍射和分子动力学研究

基本信息

批准号：
12640466
负责人：
KIHARA Kuniaki
金额：
$ 2.24万
依托单位：
Kanazawa University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2000
资助国家：
日本
起止时间：
2000 至 2001
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-12640466/
关键词：
silica mimeral melanophlogite low-high phase trasition melecalar dynamics simulation X-ray single crystal anaiysis シリカ包摂鉱物

项目摘要

1. The structure of low melanophalohite was firstly determined using specimens from Mt. Hamilton (Ca), and thenrefined with intensity data measuread on a 4-circle diffractometer. The low form, which is a superstructure of the high temperature cubic one, results in the first order phase trasition from the cubic form.2. The structural changes in a wide range of temperature from -50 to 200℃ were studied with X-ray single crystal techniques, showing the trasition point at about 70℃. Si-O distances and Si-O-Si angles, both for the atomic mean positions, show a begative correlation : Si-O decreases significantly in the range of the low form, while Si-O-Si increases.3. Some of oxygen atoms show remarkable anisotropy in atomic mean swuare displacements, suggesting a possible disorder.4. The maximum entropy method was applied to analyze electron density distribution in the high form, indicating that all the cages of pentagon dodecahedron are occupied by CH4, which are possibly in six oreintations.5. Melanophlohite releases its guest molecules at a temperature as high as 1000℃. The guest-free specimen obtained by heating up to 1000℃ belongs to the cubic space group as the same as that of natural specimens, and show no structural transition with varying temperatures. This result denies a reported one based on a NMR study.6. Some trials of MD simulations for a model structure with pentagon dodecahedral cages, fully occupied by CH4 molecules, succeeded to reproduce the structure transition from the cubic form to the (2x2x1) tetragonal superstructure. This suggests that guest molecules play important roles in the structural transitions in melanophlogite.

1。首先使用汉密尔顿山（CA）的标本确定低黑色素石的结构，然后在4圈衍射仪上对强度数据测量进行了修复。低温立方体的上层结构的低形式导致一阶从立方形式过渡。2。 X射线单晶技术在较广泛的温度中的结构变化是研究的，显示了约70℃的过渡点。 Si-O距离和SI-O-SI角度（对于原子平均位置）都显示出初学者的相关性：SI-O在低形式的范围内显着降低，而SI-O-SI则增加。3。一些氧原子在原子平均swuare位移中表现出显着的各向异性，表明可能是一种疾病。4。最大的熵方法用于分析高形式的电子密度分布，表明五角大楼十二面体的所有笼子都被CH4占据，这可能是六个Oreintations.5。黑素叶石在高达1000℃的温度下释放其客人分子。通过加热高达1000℃获得的无客体标本属于立方空间群，与天然标本相同，并且没有温度变化的结构过渡。该结果否认了基于NMR研究的报告。6。对五角大楼十字形笼子的模型结构的一些试验，完全由CH4分子占据，成功地重现了从立方形式到（2x2x1）四方超结构的结构过渡。这表明来宾分子在黑色素藻中的结构过渡中起着重要作用。