高压X射线吸收谱研究 (SiO2)x(GeO2)100-x(x=0,99-95)体系压力诱导相变机理

Glass, liquids and ice have attracted wide-spread attention owing to the structural polymorphism. Perhaps the most fundamentally important of these are the strong network-forming and tetrahedral-oxide glass such as SiO2 and GeO2. Especially, the amorphous-amorphous and amorphous-crystalline phase transition of them induced by pressure based on DAC being investigated by X-ray absorption spectroscopy (XAS) are eager for glass theory, geophysics, earth and planetary science, and photoelectric material. In this NSFC proposal, based on our new development of a directly measured method, for the first time, of high-pressure XAS without Bragg reflection from the diamond anvils, we hope to improve this method more friendly for the high-pressure XAS user in Beijing Synchrotron Radiation Facility. Using this method, we plan to measure the Ge K-edge EXAFS, without Bragg glitches from DAC, of the (SiO2)x(GeO2)100-x(x=0,99-95) system. To obtain quantitative structural information including the bond lengths and angles around Ge of higher coordination shells, multiple-scattering structural parameters fitting using the GNXAS will be than performed. Combining the ab initio molecular dynamics simulation, the medium-and short-range order information of local structure distortions, phase transition route, intermediate state and mixed phases, network-forming and destroying mechanism during the amorphous-amorphous or amorphous-crystalline phase transition induced by pressure will be explored. Meanwhile, our method will provide new high-pressure XAS based on DAC platform for the BSRF users.

结构多态性是玻璃、液态和冰等研究热点之一，而SiO2和GeO2玻璃等是研究结构多态性的强网络形成和四面体无定型经典体系。特别是利用X射线吸收谱研究基于DAC高压诱导无定型态-无定型态（或晶态）相变过程，已成为国际上玻璃理论基础研究、地质科学、地球和行星科学、光电材料等领域高压科学研究者的迫切需求。本项目依据我们首次在国际上实现的基于单晶金刚石压砧高压下无衍射峰完整EXAFS谱直接实验测量方法，依托BSRF的4W1B和1W1B站，进一步完善此方法，完成(SiO2)x(GeO2)100-x(x=0,99-95)高压Ge的K边EXAFS谱测量，通过定量拟合包括高配位壳层键长和键角局域结构，结合分子动力学的模拟，获得局域结构扭曲和相变路径、网络形成及变形机制等中短程序的信息，研究压力诱导的无定型态-无定型态和无定型态-晶态等相变，探讨其结构多态性。同时为我国用户提供良好的高压XAS公共平台。

完善了基于毛细管透镜和透射式超薄Si光电二极管X射线探测器的高压透射模式XAFS谱实验方法，提出了Si光电二极管/雪崩二极管X射线散射和荧光增强探测新方法，对第三代同步辐射光源X射线通量探测有重要意义。系统地研究了多晶GeO2，以及石英（SiO2）和类石英（GeO2、AlPO3）体系压力诱导非晶化和高压相变机理，解决了该领域二十年来压力失稳的根源的争论。建立了对轻元素体系利用掺杂重元素作为探针获得局域结构信息的高压荧光XAFS实验装置及方法,并研究了非晶GexSi1-xO2样品系列高压局域结构变化。