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

非技术综述：施加高压会极大地改变元素和化合物的物理化学性质，这导致了具有无与伦比的性能的迷人的新材料的形成。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物结构或大分子(聚氮化物)的富氮金属化合物。这些材料显示出巨大的潜力，可能成为下一代超硬或高能量密度材料。研究人员探索了特定的碱、碱土和过渡金属聚氮化物在高压和温度下的形成。然后，他们通过激光加热的钻石顶压腔、同步加速器X射线衍射和拉曼散射实验来确定材料的晶体化学和物理性质，以调整合成的压力-温度条件，并探索新型多氮化合物的结构、物理性质和化学键。这项研究将有助于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。该项目推动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助理和先进的设施(如高级光子源，APS)提供支持和培训，并为霍华德大学的研究生和本科生提供研究机会。高中生将参加暑期学徒计划。技术总结：材料特性在高压下会发生很大变化，不寻常的化学键方案和新颖的化学计量比在热力学上变得稳定。在美国国家科学基金会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、碱土和过渡金属聚氮化物(重点是Li、K、Re、Os、W、Cr、Ru、Ti、Zr、Hf)在高压高温条件下的形成及其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建各种不寻常的化学键方案和组成，这些方案和组成在高密度下变得热力学稳定，但在常压下可能是亚稳定的。研究人员在激光加热的金刚石顶压腔中结合X射线衍射和拉曼实验，为进一步放大合成奠定了基础，并揭示了不同金属的聚氮化物的合成条件、化学键、结构和性能之间的关系。这使他们能够制定晶体化学原理，控制极端条件下聚氮化物的形成和行为。此外，研究人员将化学成分、外部应变、维度、温度和化学前体作为关键变量，可用于在适合实际应用和亚稳态回收材料的压力-温度范围内进行合成。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.