RII Track 4: Understanding Defect Chemistry in Sodium Chalcogenide Superionic Conductors by Advanced Neutron Technology

固态钠（Na）超导体在传感器和固态钠电池中发挥着重要的作用。硫系钠离子导体由于具有高的钠离子电导率和冷压包覆致密化特性而受到广泛关注。对于这些导体，其晶体结构中存在的Na缺陷（即空位或间隙）强烈影响其离子电导率。因此，更好地了解这种细微的结构变化对于硫系钠离子导体的合成和掺杂具有重要意义。一个主要的挑战是很难通过常规的x射线衍射技术准确地捕捉到细微的缺陷结构。该项目利用中子的高分辨率进入橡树岭国家实验室（ORNL）的先进中子设施，在那里，PI和她的合作者将研究Na3SbS4-xSex材料的晶体结构，以获得硫系导体缺陷化学的基本知识。本研究成果将促进高性能固态钠电池新型固体电解质的开发。此外，该项目将建立路易斯维尔大学（UofL）和ORNL之间的长期合作关系，这是一个桥梁，使肯塔基大学的其他院系受益，以促进在边界材料科学领域的更多合作研究。硫系钠超离子导体（即Na3PCh4和Na3SbCh4 (Ch=S, Se)）在固态钠电池中具有很大的应用潜力。在这些导体中，缺陷化学（如Na空位）显著影响离子在晶体框架中的传输。本研究的目的是利用Na3SbS4-xSex导体作为模型材料，了解缺陷变化背后的物理原理，揭示缺陷局部结构如何影响Na+离子扩散。通过与ORNL散裂中子源（SNS）中子科学家的合作研究，我们的目标是推进目前最先进的对缺陷化学及其对硫系na离子导体中多晶态和离子传输的影响的理解。本研究将涉及：(1)利用原位中子衍射密切观察Na3SbS4-xSex导体的相形成并跟踪其Na缺陷等细微结构变化；(2)揭示Se掺杂对Na3SbS4-xSex导体晶体结构（相稳定性和Na缺陷动力学）以及离子在晶体间扩散的影响。该工作的成功证明将为研究Na3SbS4-xSex硫系导体的合成和离子输运提供新的基础认识。所获得的知识不仅将为理解其他含缺陷的晶体Na离子导体铺平道路，而且还将促进固态Na电池中新型固体电解质的开发，以用于未来的储能。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Solid-state sodium (Na) superionic conductors play a significant role in applications for sensors and solid-state Na batteries. Chalcogenide Na-ion conductors have attracted intense attentions due to high Na+ ionic conductivity and cold-press included densification. For these conductors, the presence of Na defects (i.e. vacancies or interstitials) in their crystal structures strongly influence their ionic conductivities. Thus, it is essential to better understanding on the subtle structural change for the synthesis and doping of chalcogenide Na-ion conductors. One main challenge is the difficulty to accurately catch the subtle defect structure through regular X-ray diffraction technology. This project takes advantages of high resolution of neutrons to access advanced neutron facilities at Oak Ridge National Laboratory (ORNL), where the PI and her collaborators will investigate the crystal structures of Na3SbS4-xSex materials to obtain the fundamental knowledge of defect chemistry in chalcogenide conductors. The findings of this research will promote the development of new solid electrolytes for high performance solid-state Na batteries. In addition, this project will establish a longstanding collaboration between University of Louisville (UofL) and ORNL, which is a bridge to benefit other faculties at Kentucky to foster more collaborative research in boarder materials science fields. Chalcogenide Na superionic conductors (i.e. Na3PCh4 and Na3SbCh4 (Ch=S, Se)) have great potential for applications in solid-state Na batteries. In these conductors, defect chemistry such as Na vacancies significantly affect the ion transport across crystal frameworks. The goal of this proposed research is to use Na3SbS4-xSex conductors as model materials to understand the physical principle underlying the defect changes and reveal how the defect local structures influence the Na+ ion diffusion. Through a collaborative research with neutron scientists in Spallation Neutron Source (SNS) at ORNL, we aim to advance the current state-of-the-art understanding on defect chemistry and their effects on the polymorphs as well as ion transport in chalcogenide Na-ion conductors. This research will involve: (1) Employ in situ neutron diffraction to closely observe phase formation and track the subtle structure changes such as Na defects for Na3SbS4-xSex conductors; (2) Reveal the Se doping effects on the crystal structure (phase stability and Na defect dynamics) as well as the ion diffusion across crystals of Na3SbS4-xSex conductors. The successful demonstration of the proposed work will provide a new fundamental understanding on the synthesis and ion transport in Na3SbS4-xSex chalcogenide conductors. The obtained knowledge will not only pave the way to understand other defects-contained crystalline Na-ion conductors, but also promote the development of new solid electrolytes in solid-state Na batteries for future energy storage.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.