Excellence in Research - Exploring Frontiers in Novel Material Synthesis at High Pressures: Synthesis and Recovery of Superhard and High Energy-Density Polynitrides

非技术性总结：施加高压会极大地改变元素和化合物的物理和化学性质，从而形成具有无与伦比性能的迷人新材料。在NSF综合活动办公室的支持下，霍华德大学和华盛顿卡内基研究所的研究人员研究了在高压下形成聚合结构或大分子（多氮化物）的富氮金属化合物。这些材料显示出作为下一代超硬或高能量密度材料的巨大潜力。研究人员探索在高压和高温下形成特定的碱金属、碱土金属和过渡金属多氮化物。然后，他们使用激光加热金刚石对顶砧单元，同步加速器X射线衍射和拉曼散射实验的组合来确定材料的晶体化学和物理特性，以调整合成的压力-温度条件，并探测新型多氮化合物的结构，物理特性和化学键合。这项研究可以帮助和指导未来具有工业相关性质的新型多氮化合物的功能设计。该项目推进了材料科学领域，寻找具有潜在能源应用的新材料，以及地球和行星科学的邻近领域，这将受益于在极端条件下更好地了解晶体化学。该项目为霍华德大学/卡内基科学研究所的一名博士后提供支持和培训，并提供先进的设施（如先进光子源，APS），以及为霍华德大学的研究生和本科生提供研究机会。高中生将通过暑期学徒计划参与。技术总结：材料性质在高压下会发生很大变化，不寻常的化学键合方案和新颖的化学计量变得化学稳定。在NSF综合活动办公室的支持下，霍华德大学和华盛顿卡内基研究所的研究人员研究了碱金属、碱土金属和过渡金属多氮化物（重点是Li、K、Re、Os、W、Cr、Ru、Ti、Zr、Hf）在高压高温条件下的形成，以及它们的晶体化学和物理性质。研究人员利用压力作为一种工具来创造各种不寻常的化学键合方案和组合物，这些化学键合方案和组合物在高密度下变得稳定，但在环境压力下可能是亚稳定的。利用X射线衍射和激光加热金刚石对顶砧中的拉曼实验相结合，研究人员为进一步扩大合成奠定了基础，并揭示了不同金属多氮化物的合成条件，化学键合，结构和性能之间的关系。这使他们能够制定晶体化学原则，在极端条件下控制多氮化物的形成和行为。此外，研究人员操纵化学成分，外部应变，维度，温度，和化学前体作为关键变量，可用于在压力下进行合成-该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查进行评估，被认为值得支持的搜索.

Non-technical summary: Applying high pressure drastically changes physical and chemical properties of elements and compounds, which leads to the formation of fascinating new materials with unmatched properties. With support from NSF’s Office of Integrative Activities, researchers at Howard University and Carnegie Institution of Washington investigate nitrogen-rich metal compounds that form polymeric structures or large molecules (polynitrides) under high pressure. These materials show great promise as possible next-generation superhard or high-energy-density materials. The researchers explore the formation of specific alkali, alkali-earth and transition metal polynitrides at high-pressures and temperatures. Then they establish the material’s crystal chemistry and physical properties using a combination of laser-heated diamond anvil cells, synchrotron X-ray diffraction and Raman scattering experiments to tune the pressure-temperature conditions of synthesis and to probe the structure, physical properties, and chemical bonding of novel polynitrogen compounds. This research could aid and direct the functional design of new polynitrogen compounds with industrially relevant properties in the future. The project advances the Materials Science field in the search for new materials with potential energy applications as well as adjacent fields in Earth and Planetary sciences, which would benefit from better knowledge of crystal chemistry at extreme conditions. The project provides support and training to one postdoctoral associate at Howard University/Carnegie Institution for Science and advanced facilities (e.g. Advanced Photon Source, APS), as well as research opportunities for graduate and undergraduate students at Howard University. High school students will be engaged through a summer apprenticeship program.Technical summary: Material properties are greatly altered at high pressures, where unusual chemical bonding schemes and novel stoichiometries become thermodynamically stable. With support from NSF’s Office of Integrative Activities, researchers at Howard University and Carnegie Institution of Washington study the formation of alkali, alkali-earth and transition metal polynitrides (with focus on Li, K, Re, Os, W, Cr, Ru, Ti, Zr, Hf) at high-pressure high-temperature conditions, and their crystal chemistry and physical properties. The researchers exploit pressure as a tool to create a variety of unusual chemical bonding schemes and compositions, which become thermodynamically stable at high densities, but can be metastable at ambient pressure. Using a combination of X-ray diffraction and Raman experiments in laser-heated diamond anvil cell the researchers build a basis for further scaling-up of the synthesis, and reveal relations between synthesis conditions, chemical bonding, structure, and properties of polynitrides of different metals. This enables them to formulate crystal chemical principles governing the formation and behavior of polynitrides at extreme conditions. Furthermore, the researchers manipulate chemical composition, external strain, dimensionality, temperature, and chemical precursors as key variables that can be used to perform synthesis in the pressure-temperature range suitable for practical application and for metastable recovery of the materials.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.