极端条件下元素液体（Se和I2）的结构和性质研究

The structure and properties of materials under extreme conditions (high temperature and high pressure) are of great interesting in condensed matter physics, material science, and geophysics. Consequently, the structure phase transition and properties of crystal materials were investigated widely in the past decades. However, because of the absence of periodicity in the structure, the theories of crystal are no longer valid for liquids, which leads to great difficulties in structure and properties study on liquids. There are no universal structure models and theories for liquid to date. The knowledge of liquid is an important constituent part of the knowledge of condensed matter, and is crucial for people to understand the matter and energy transportation in the interior of the Earth. In the present study, we focus on the elemental liquids of selenium and iodine. We plan to investigate the structures of liquid selenium and iodine at high pressures and high temperatures by X-ray diffraction/scattering technologies. We also plan to determine the density, viscosity and sound velocity of liquid selenium and iodine as a function of pressure and/or temperature. We try to figure out how the structure evolves with increasing pressure and temperature, and the relationship between the structure transition and the properties change of liquid. These results are valuable data for establishing the universal structure model and theories for liquid.

极端条件（高温高压）下物质的结构和性质是凝聚态物理、材料科学和地球科学等学科关注的重要课题。因此，众多研究者对晶体材料在极端条件下的结构相变和物性进行了广泛而深入的研究。与晶体材料相比，液体由于长程周期性的缺失，基于晶体平移周期性的方法与理论对液体不再适用，这使得液体的结构和物性研究变得困难重重。至今尚未建立液体普适的结构模型和理论框架。而对液体的认识是认识凝聚态物质的重要组成部分，也是人类认识地球内部物质和能量输运过程的知识基础。本项目以液体Se和I2为研究对象，通过X射线衍射/散射技术来研究其结构随温度和压力的变化。同时，对结构变化过程中液体Se和I2的密度、粘度和声速等性质进行系统测量。试图弄清基本元素液体在高温高压条件下的结构如何演变？以及液体Se和I2性质突变与结构相变之间有何关系？为液体结构模型及相变理论的研究提供重要的实验数据。

长程周期性的缺失使得液体结构及相变的研究较之晶体而言显得极其困难。极端条件下（高温高压）液体结构和物性的研究对凝聚态物理和地球科学而言具有重要的基础性意义。本项目综合利用基于同步辐射的X射线散射技术，X射线成像技术，X射线吸收扫描技术和超声测量技术对元素液体（Se，I2和S）在高温高压条件下的结构和物性进行了较系统的研究。通过对S和Se液体结构和物性的系统对比研究，发现了聚合态液体在相变过程中结构和物性之间可能存在的普适关系。利用X射线散射技术测量了液态Se的结构随压力和温度的变化。发现在低温低压条件下液态Se具有链状结构。而在高温高压条件下，液态Se形成了三维的网状结构。利用超声测量技术，确认了液态I2在高温高压条件下存在两个液体-液体相变。同时，发展了适用于高压下无定形态和液体材料密度测量的实验方法。该研究加深了对极端条件下液体结构相变的认识，为液体结构模型及相变理论的研究提供重要的实验数据。