静态超高压下氢的晶体结构实验研究

在极端条件下,固态氢会经历一系列相变,理论预测其在足够高的压力下会演变为金属。由于金属氢被预测具有室温超导和超流等特性,其研究受到了学界的极大关注。然而,研究金属氢存在巨大的技术挑战:一方面,达到氢金属化的压力条件极为苛刻,至今对冷压下是否已制备出金属氢仍未达成共识;另一方面,超高压下氢的精确表征十分困难,特别是表征固态氢晶体结构的技术手段更是严重滞后。晶体结构作为了解一种材料的最基本信息,对其认知的匮乏阻碍了理解氢在高压下如何逐步演化为金属氢的过程。为此,着眼于超高压氢的晶体结构测量,发展了一套先进同步辐射X射线衍射方法,在室温下将氢的晶体结构测量扩展至254 GPa,将相关压力记录提高了一倍。介绍了相关的技术突破,探讨了在超高压下对氢进行晶体结构测量的方法以及存在的问题,以期为在更高压力条件下测量氢的结构信息做好铺垫。

Crystallographic Studies of Ultra-dense Solid Hydrogen

Under extreme compression,hydrogen goes through a series of phase transitions,and may transform to an exotic metal predicted by theoretical calculations.The pursuit of metallic hydrogen by the high pressure community is intense due to the predicted room temperature superconductivity and superfluidity.Unfortunately,significant technical obstacles present for such studies.On one hand,achieving the pressure of metallic hydrogen is daunting,as a result,there has been no consensus on the success synthesis of cold compressed metallic hydrogen yet.On the other hand,accurate characterizations of ultra-dense hydrogen remain very difficult,especially for measuring crystal structure.The lack of crystal structural information(the most fundamental information of a material)of hydrogen prevents understanding how does hydrogen evolves structurally to achieve the predicted metal from an insulating solid.In order to measure the crystal structure of hydrogen at ultrahigh pressures,we developed a series of advanced synchrotron X-ray diffraction techniques,and extended the crystal structural data of hydrogen to 254 GPa,which doubled the previous pressure record.In this paper,we will introduce our technical developments and discuss the related issues,in order to provide guidance for measuring crystallographic data of solid hydrogen at higher pressures.