Megabar Neutron Diffraction for Hydrogen, Ices and Superconductor Research MENHIR

对于由分子组成的系统来说，100万大气压左右的压力是一个重要的里程碑。这个值附近的压力需要打破将分子结合在一起的强共价键，从而将分子系统转变为非分子系统。这种从分子到非分子的变化导致了性质的深刻变化。据报道，氢变成了一种金属，这种金属形式可能是木星磁场的原因。水和冰中的氢原子与氧原子分离，变得可移动，因此它们的导电方式类似于笔记本电脑和手机电池中的锂离子的导电方式。硫化氢形成一种金属化合物，它在零下70摄氏度的温度下就会超导。对这些现象和类似现象的研究产生了具有基础和技术重要性的信息。例如，氢原子的行为为我们对量子行为的理解提供了严格的测试，像冰这样的氢键固体的行为方式为生化过程的工作方式提供了洞察，新型超导体为潜在的室温超导体提供了新的途径，这将改变电力分配医学成像，并可能使“回到未来II”的悬浮板成为现实。然而，我们对这些和其他重要的富氢系统在百万大气压下的理解是有限的，因为最基本的信息——氢原子在晶体结构中的位置——目前还不知道。缺乏信息的原因是，中子衍射是唯一能够直接测量氢原子位置的技术，直到最近才被限制在30万大气压以下的压力下，因此关于氢原子位置的信息必须间接或从计算模型中获得。在过去的七年中，我们一直在开发使用美国橡树岭国家实验室的SNAP仪器和散裂中子源进行中子衍射研究的合适技术。我们现在已经达到了在超过一百万大气压的压力下使用粉末和单晶衍射技术成功确定结构的阶段。该项目旨在使用所谓的钻石砧细胞，将样品压缩在两个大的宝石级钻石之间，以研究氢、冰和相关冰（半水合氨和氯化氢）的结构，以及高达百万大气压的高温超导体。

The pressure of around one million atmospheres is an important milestone for systems composed of molecules. Pressures around this value are required to break the strong covalent bonds which hold molecules together and hence transform molecular systems into non-molecular systems. This change from molecular to non-molecular leads to profound changes in properties. Hydrogen has been reported to become a metal and this metallic form may be the cause of Jupiter's magnetic field. The hydrogen atoms in water and ice detach from the oxygen atoms and become mobile so that they conduct electricity in a way similar to the way that lithium ions in the batteries of laptops and phones conduct. Hydrogen sulphide forms a metallic compound which superconducts at a temperature of only -70 C. A study of these and similar phenomena yields information that is of both fundamental and technological importance. For example, the behaviour of hydrogen atoms provides stringent tests for our understanding of quantum behaviour, the way hydrogen-bonded solids like ice behave provides insight into the way biochemical processes work, and novel superconductors offer new routes to a potential room temperature superconductor which would transform power distribution medical imaging and could make a 'Back To The Future II' hoverboard a reality. However, our understanding of these and other important hydrogen-rich systems at million atmosphere pressures is limited by the fact that the most fundamental information -- the position of the hydrogen atoms in the crystal structures -- is currently not known. The reason for this lack of information is that neutron diffraction which is the only technique able to measure hydrogen atom positions directly was until recently restricted to pressures below 300,000 atmospheres and so information on the positions of the hydrogen atoms had to be obtained indirectly or from computational modelling. For the past seven years we have been developing the use of suitable technology for neutron diffraction studies using the SNAP instrument and the Spallation Neutron Source at Oak Ridge National Laboratory in the United States. We have now reached the stage where structures can be successfully determined at pressures in excess of one million atmospheres using both powder and single crystal diffraction techniques.This project aims to use a so called diamond anvil cell where the sample is compressed between two large gem quality diamonds to study the structures of hydrogen, ice and related ices (ammonia hemihydrate and hydrogen chloride), and very high Tc superconductors up to million atmosphere pressures.