What did the Scientists Discover?
Understanding the mechanisms of charge transport in spinels has the potential to establish design principles for enhancing their electronic and electrochemical properties for energy storage applications such as super capacitors. Researchers investigated ternary CoxMn3−xO4 spinel nanoparticles at CHESS exploiting the unique sensitivity of X-ray emission spectra to precisely determine the valence states and local coordination environments of Mn and Co as function of spinel composition. They found that the stochiometric trend in electronic conductivity correlates well with the concentration of Mn4+/Mn3+ hopping pairs, while the concentration of Mn3+/Mn2+ pairs is unchanged with stoichiometry. Co does not directly contribute to conductivity but creates configurational disorder that leads to the generation of hopping pairs for Mn at octahedral sites.
Broader Impacts of this work?
One of the main limitations identifying more accurate descriptions of charge transport in oxides has been the lack of characterization methods to precisely determine the site occupation of the cations. Overcoming these challenges by employing XES as in this study will lead to a more detailed understanding of the cation site occupancy with the ultimate goal of uncovering the fundamental link between configurational disorder and material properties. Combined with information on the material properties, we can then adjust the design principles to create better performing energy devices.
Why is this important?
Mixed-valence ternary spinel oxides exhibit electronic and electrochemical properties that can be significantly improved relative to those of binary spinel oxides. While it is known that the presence of multiple cation species at different sublattice sites gives rise to enhanced transport properties, the exact nature of this enhancement is poorly understood. This work forms the starting point to understanding the mechanisms of charge transport in ternary spinel systems.
Why did this research need CHESS?
This research used the two-color x-ray emission spectrometer DAVES at CHESS C-line to record the Co and Mn Kβ X-ray emission lines. The spectrometer enables rapid switching between collecting Co and Mn data essential for this research.
- Anuj Bhargava, Department of Materials Science and Engineering, Cornell University
- Cindy Y. Chen, Department of Materials Science and Engineering, Cornell University
- Kapil Dhaka, Department of Materials Science and Engineering, Technion - Israel Institute of Technology
- Yuan Yao, Department of Materials Science and Engineering, Cornell University
- Andrew Nelson, Department of Materials Science and Engineering, Cornell University
- Kenneth D. Finkelstein, Cornell High Energy Synchrotron Source (CHESS), Cornell University
- Christopher J. Pollock, Cornell High Energy Synchrotron Source (CHESS), Cornell University
- Maytal Caspary Toroker, Department of Materials Science and Engineering, The Nancy and Stephen Grand Technion Energy Program, Technion - Israel Institute of Technology
- Richard D. Robinson, Department of Materials Science and Engineering, Cornell University
A. Bhargava et al., “Mn Cations Control Electronic Transport in Spinel CoxMn3−xO4 Nanoparticles,” Chemistry of Materials, vol. 31, no. 11, pp. 4228–4233, 2019. https://doi.org/10.1073/pnas.1817134116
How was the work funded?
Cornell High Energy Synchrotron Source (CHESS) is supported by the National Science Foundation under award number DMR-1332208. This work was also supported by the National Science Foundation (NSF) under award numbers DMR-1809429, CMMI-1344562, CHE-1507753, DMR-1149036 and DMR-1719875; by a grant from the United States-Israel Binational Science Foundation (BSF), Jerusalem, Israel.