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

本工作的目的是研究由SNI_4压力引起的非晶化过程的机制，SNI_4是由四面体分子组成的分子晶体。主要目标是建立一种实验技术，以确定在高压下收集的同步X射线衍射数据，并获得金属无定形SNI_4的详细结构知识。在第一个财政年度，我们在第一个财政年度中，我们设计并在BL04B2上设计了一个新的钻石小组（DAC）设备（DAC）设备，并构建了一个新的钻石小区（DAC）。首先测量35、45和55 GPA时金属无定形SNI_4的衍射模式。阐述了可靠散射强度的估计，我们最终在每种压力下获得了结构因子s（q）和降低的径向分布函数g（r）。检查G（R），我们发现SNI4分子不再存在于35至55 GPa之间的无定形状态，其G（R）显示了由硬球的密集随机堆积形成的无定形结构的许多特征。 SNI_4的衍射研究表明，在2.5 GPA时，减压时有一个无定形的相变，并伴随着SNI_4分子的重建。其他研究包括在高温和高压下从无定形状态的重结晶，在静水条件下的无形化以及利用核向前散射的高压下的摩斯鲍尔光谱。检查非晶状态的热力学稳定性，其原子尺度结构及其电子结构，我们现在讨论了SNI_4中压力诱导的无形化过程的机制。这项研究结果的部分在2001年8月的第18届Airapt International Conferition（Beijin）上介绍