Nitrogen under Extreme Conditions: From Fundamental Physics to Novel Functional Materials

过去400年的技术发展主要依赖于对物质基本行为的理解的逐步增加，而这反过来又有助于形成突破性的功能材料。在我们的现代社会中，两种最重要的材料是高能量密度和超硬固体。高能量密度材料（HEDM）被用作采矿炸药-每年用于从地球提取必需矿物质的数亿吨-以及火箭燃料。它们是密集研究的主题，以寻找更高性能和无污染的替代品。另一方面，超硬材料代表着一个不断增长的数十亿国际市场，对于从机械加工工具到医疗假肢，再到航空航天、光学甚至珠宝等广泛应用来说都是不可或缺的。虽然金刚石被认为是至高无上的超硬材料，但它的低耐磨性和化学稳定性使其不足以用于许多必须找到替代品的应用。氮的显着特性使其成为新突破的HEDM和超硬材料的理想元素。事实上，共价氮-氮单键是所有元素中能量最高的键，储存和释放的能量比目前最好的HEDM高出近十倍。氮气HEDM是完全环保的。同时，氮共价键也是超硬的，能够形成超硬固体。虽然氮在技术材料方面的特殊潜力已经被人们知道了几十年，但经典的方法已经被证明不足以生产有吸引力的富氮化合物。近年来，材料合成的一个新参数已经成为实现广受欢迎的氮基工业材料的最佳竞争者：压力。事实上，压缩到大气压力的数百万倍，从根本上改变了物质的行为，有利于新的和奇异的原子排列，这些排列在其他情况下是无法实现的，例如非常令人向往的高能和超刚性氮共价键。作为关键的第一步，将对控制分子氮（N2）高压行为的物理化学力进行实验研究。然后，在与理论家的合作努力中，将详细阐述一个新的理论框架，以解决第一原理预测的缺点，并显着提高其准确性，这对工程设计新型氮基功能材料至关重要。在第二步中，将实验研究用于形成高能量密度以及超硬固体的最有前途的氮二元系统。所有压力产生的化合物将进行表征，以确定其确切的性质和特性，以及确定其作为工业材料的潜在用途。这项工作只能通过利用最近开发的技术成功实现：多晶样品的同步加速器单晶X射线衍射（SC-XRDp）。该研究项目将在爱丁堡大学的极端条件科学中心（CSEC）进行，该中心是高压科学领域的世界知名机构，拥有成功实现该研究项目所需的必要工具和专业知识。压力参数有望成为最终揭示氮气全部潜力的关键。利用一种新的实验方法，我们对极端条件下物质的理解将比以往任何时候都更进一步，为新型功能材料的设计开创了一个新时代。所发现的固体无疑将在未来几十年的技术突破中发挥关键作用。

The technological developments seen in the last 400 years largely rest on incremental increases of the understanding of the fundamental behaviour of matter, in turn exploited to enable the formation of breakthrough functional materials. In our modern day societies, two of the most important class of materials are high energy density and superhard solids. High energy density materials (HEDMs) are employed as mining explosives-with hundreds of millions of tons annually used to extract essential minerals from the Earth-and as rocket fuel. They are the subject of intense research to find higher performance and non-polluting alternatives. On the other hand, superhard materials represent a growing multibillion international market and are indispensable for a wide range of applications, from machining tools to medical prosthetics, passing through aerospace, optics and even jewellery. While diamond is considered the sovereign superhard material, it low abrasiveness and chemical stability makes it inadequate for a number of applications for which an alternative must be found.The remarkable characteristics of nitrogen make it the ideal element for new breakthrough HEDMs and superhard materials. Indeed, covalent nitrogen-nitrogen single bonds are the most energetic bonds among all elements, storing and releasing close to ten times more energy than the current best HEDMs. Nitrogen HEDMs are entirely eco-friendly. At the same time, nitrogen covalent bonds are also ultra-stiff, enabling the formation of superhard solids. While the exceptional potential of nitrogen for technological materials has been known for decades, classical approaches have proven inadequate in producing attractive nitrogen-rich compounds. In recent years, a new parameter for material synthesis has established itself as a top contender for achieving the sought-after nitrogen-based industrial materials: pressure. Indeed, compression to millions of times the atmospheric pressure radically changes the behaviour of matter and favours new and exotic atomic arrangements that are predominantly inaccessible otherwise, such as the greatly desirable high energy and ultra-stiff nitrogen covalent bonds.This research project aims at exploiting the high pressure approach to harness the tremendous potential of nitrogen to produce new technological materials. As a crucial first step, the physico-chemical forces governing the high pressure behaviour of molecular nitrogen (N2) will be experimentally investigated. Then, in a collaborative effort with theorists, a new theoretical framework will be elaborated to address the shortcomings of first-principles predictions and significantly increase their accuracy-essential for engineering novel nitrogen-based functional materials. In a second step, the most promising nitrogen binary systems for forming high energy density as well as superhard solids will be experimentally studied. All pressure-produced compounds will be characterized to determine their exact nature and properties, as well as to establish their potential use as industrial materials. This work can only be successfully achieved by exploiting a recently developed technique: synchrotron single-crystal X-ray diffraction from polycrystalline samples (SC-XRDp). This research project will take place at the Centre for Science at Extreme Conditions (CSEC) of the University of Edinburgh-a world-renowned institution in the field of high pressure sciences with the necessary tools and expertise required for the successful realization of this research project.The pressure parameter promises to be key to finally unravel the full potential of nitrogen. Exploiting a novel experimental method, the boundaries of our understanding of matter under extreme conditions will be pushed further back than ever before; ushering a new era for the design of novel functional materials. The discovered solids will undoubtedly play a pivotal role in the upcoming decades' technological breakthroughts.