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

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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.