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Structure analysis of pressure-induced amorphous state of a molecular crystal with tetrahedral molecules

四面体分子晶体压力诱导非晶态结构分析

基本信息

批准号：
12640309
负责人：
HAMAYA Nozomu
金额：
$ 2.24万
依托单位：
Ochanomizu 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

项目摘要

The objective of the present work is to study a mechanism of amorphization process induced by pressure in SnI_4, a molecular crystal consisting of tetrahedral molecules. Major goals are to establish an experimental technique for determination of amorphous structure from synchrotron x-ray diffraction data collected at high pressure and to obtain detailed structural knowledge of metallic amorphous SnI_4 in a wide pressure range.In the first fiscal year, we designed and constructed a new diamond anvil cell (DAC) device and prepared some instruments at BL04B2 at SPring-8 for the present study. Diffraction patterns of metallic amorphous SnI_4 at 35, 45 and 55 GPa were measured first. Elaborating an estimation of reliable scattering intensities, we finally obtained the structure factor S(Q) and the reduced radial distribution function G(r) at each pressure. Inspecting G(r) we found that the SnI4 molecules are no longer existent in the amorphous state between 35 and 55 GPa and that its G(r) shows many features of the amorphous structure formed by the dense random packing of hard spheres.In the second fiscal year, various studies were conducted. Diffraction study of SnI_4, revealed that at 2.5 GPa on decompression there is an amorphous-amorphous phase transition accompanied by the re-formation of the SnI_4 molecules. Other studies include the recrystallization from the amorphous state at high temperature and high pressure, the amorphization under hydrostatic condition and the Mossbauer spectroscopy at high pressure utilizing the nuclear forward scattering. Examining thermodynamic stability of the amorphous state, its atomic-scale structure and its electronic structure, we now discuss the mechanism of the pressure-induced amorphization process in SnI_4.Part of the results of this study were presented at the 18th AIRAPT International Conference (Beijin) in Aug., 2001 and the 11th International Conference on Liquid and Amorphous Metals (Yokohama) in Sep., 2001

本文的目的是研究由四面体分子组成的分子晶体SnI_4中压力诱导非晶化过程的机理。主要目的是建立一种利用高压同步x射线衍射数据测定非晶态结构的实验技术，并在宽压力范围内获得金属非晶态SnI_4的详细结构知识。在第一财年，我们设计并构建了一个新的金刚石砧细胞（DAC）装置，并在SPring-8在BL04B2准备了一些仪器用于本研究。首先测定了金属非晶态SnI_4在35、45和55 GPa下的衍射图样。通过对可靠散射强度的估计，我们最终得到了各压力下的结构因子S(Q)和简化后的径向分布函数G(r)。通过对G(r)的检测发现，在35 ~ 55 GPa之间，sn4分子不再处于非晶态，其G(r)表现出由硬球密集随机堆积形成的非晶态结构的许多特征。在第二个财政年度，进行了各种研究。对sn_4的衍射研究表明，在2.5 GPa的压力下，sn_4发生了非晶-非晶相变，并伴有sn_4分子的重新形成。其他研究还包括高温高压下的非晶态再结晶、流体静力条件下的非晶态以及利用核正向散射的高压穆斯堡尔光谱。考察了非晶态的热力学稳定性、原子尺度结构和电子结构，讨论了sn_4压力诱导非晶态形成的机理。本研究的部分成果已在2001年8月第18届AIRAPT国际会议（北京）和2001年9月第11届液体和非晶金属国际会议（横滨）上发表