Expanding known binary technetium nitrides and sulfides: A computationally-led synthesis program

第一部分：非技术领域的SUMMARY氚是一种放射性元素，与邻近元素相比，它的基础固态化学还不是很成熟。由于缺乏对氚的了解，限制了人们对元素周期表上围绕着它的过渡金属的理解。仅由锶和氮或硫组成的固体几乎没有被勘探过。然而，这些化合物对于理解元素的基本化学和开发具有特殊硬度或有用的电子性能的材料都是重要的。这项研究由材料研究部的固态和材料化学计划和既定的促进竞争研究计划(EPSCoR)支持，使用高压/高温合成方法来制备和表征一系列新的氮化锶和硫化物。通过使用尖端的计算方法来指导合成工作并帮助理解产生的新固体，合成生产率得到了提高。使用量子力学方法进行更详细的计算，将在实验团队试图合成这些相之前向他们提供预测的光谱和其他物理性质，从而能够快速识别，并为如何开始表征新材料提供见解。通过国家原子测试博物馆为在校学生和普通公众建立了外联活动，其目的不仅是让他们了解辐射和核过程背后的科学，而且进一步激发他们对科学的想象力。第二部分：技术总结本项目填补了二元氚化合物固态化学基础知识的重大空白。新的固态氮化物和硫化物的定向合成依赖于金刚石砧座(DAC)，再加上电阻加热(最高可达1200K)和激光加热(超过5000K)。在合成过程中，通过X射线衍射(XRD)、光谱(XAS)技术和内部光学光谱技术对DAC中进行的反应进行现场监测。晶体结构预测搜索确定了哪些化合物足够稳定，可以合成。通过计算比较竞争相压力范围内的自由能，可以针对可能形成所需化合物的非常具体的实验条件。机器学习方法将被用来从这个数据库中提取经验的反应势，这些数据可以用于预测比基于第一原理的结构搜索技术最初可访问的更多成分和结构复杂的相。这些工具还将使该团队能够准确地模拟传统电子结构方法无法达到的长度和时间尺度的系统。由于模拟和实验为稳定性的动力学和热力学方面提供了一个更好的图景，对调整结构和组成的详细了解可能被用来合理设计材料。通过国家原子测试博物馆为在校学生和普通公众建立了外联活动，其目的不仅是让他们了解辐射和核过程背后的科学，而且进一步激发他们对科学的想象力。该项目由材料研究部的固态和材料化学项目和既定的激励竞争性研究计划(EPSCoR)支持。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。

PART I: NON-TECHNICAL SUMMARYTechnetium is a radioactive element, and its fundamental solid state chemistry is not well established in comparison to neighboring elements. This lack of understanding of technetium limits what may be understood regarding the transition metals that surround it on the periodic table. Solids composed of only technetium and either nitrogen or sulfur are nearly unexplored. However, such compounds are both important in understanding the fundamental chemistry of the element and of importance to developing materials with exceptional hardness or useful electronic properties. This investigation, supported by the Solid State and Materials Chemistry program in the Division of Materials Research and the Established Program to Stimulate Competitive Research (EPSCoR) uses high pressure/high temperature synthesis methods to prepare and characterize a range of new examples of technetium nitrides and sulfides. Synthesis productivity is enhanced by using cutting-edge computational approaches to guide synthesis efforts and to assist in understanding the new solids produced. More detailed calculations using quantum mechanical methods will provide predicted spectra and other physical properties to the experimental team before they attempt to synthesize these phases, enabling quick identification and providing insights into how to begin characterizing new materials. Outreach has been established through the National Atomic Testing Museum for school students and the general public, designed not only to inform them of the science behind radiation and nuclear processes, but to further excite their imagination about science. PART II: TECHNICAL SUMMARYThis project fills in critical gaps in fundamental knowledge of the solid state chemistry of binary technetium compounds. Targeted synthesis of new solid-state nitrides and sulfides relies upon diamond anvil cells (DACs), coupled with resistive heating (fully uniform up to 1200 K) and laser heating (in excess of 5000 K). Reactions carried out in DACs are monitored in situ during synthesis through X-ray diffraction (XRD) and spectroscopic (XAS) techniques and in-house optical spectroscopy. Crystal structure prediction searches identify which compounds are sufficiently stable that they might be synthesized. By comparing free energies across pressure ranges for competing phases computationally, very specific experimental conditions where desired compounds are likely to form can be targeted. Machine learning approaches will be used to extract empirical, reactive potentials from this library of data which can be applied to the prediction of more compositionally and structurally complicated phases than will be initially accessible with first principles-based structure search techniques. These tools will also enable the team to accurately simulate systems at length and time scales inaccessible to conventional electronic structure methods. As simulation and experiment provide an improved picture of the kinetic and thermodynamic aspects of stability, a detailed understanding of adjusting structure and composition may be exploited to rationally design materials. Outreach has been established through the National Atomic Testing Museum for school students and the general public, designed not only to inform them of the science behind radiation and nuclear processes, but to further excite their imagination about science. This project is supported by the Solid State and Materials Chemistry program in the Division of Materials Research and the Established Program to Stimulate Competitive Research (EPSCoR).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.