Nearest neighbors and beyond: Reciprocal space imaging of ionic correlations in intercalation compounds

Elke Arenholz, CHESS

"The ability to generate a real-space ‘image’ of interatomic vectors from reciprocal space data, makes this technique a powerful tool in the investigation of intercalation compounds, "

Comparison of the real-space model of sodium ions in the x = 0 plane at 50K (top) with the deviation of the pair distribution function peak intensities from average, ΔPDF, (bottom) which is the basis of the model. ΔPDF peaks are at interatomic vectors connecting sites that are occupied with a greater (red) or lesser (blue) probability than random.

Comparison of the real-space model of sodium ions in the x = 0 plane at 50K (top) with the deviation of the pair distribution function peak intensities from average, ΔPDF, (bottom) which is the basis of the model. ΔPDF peaks are at interatomic vectors connecting sites that are occupied with a greater (red) or lesser (blue) probability than random.

What did the Scientists Discover?
The intercalation of alkali ions into layered materials plays an essential role in battery technology. Coulomb repulsion between the intercalants leads to ordering of the intercalant sublattice, which hinders ionic diffusion and impacts battery performance. While conventional X-ray diffraction can identify long-range order occurring at discrete intercalant concentrations, it cannot determine short-range order at other concentrations that disrupt ionic mobility. Here researchers use real-space transformations of single-crystal diffuse scattering, measured with high-energy synchrotron X-rays at CHESS, to determine ionic correlations in Na-intercalated V2O5.

Why is this important?
The ability to generate a real-space ‘image’ of interatomic vectors from reciprocal space data, makes this technique a powerful tool in the investigation of intercalation compounds, as it is especially suited to the measurement of ionic correlations on a sublattice that is distinct from the host structure. The method allowed the authors to show that the apparent order-disorder transition reported in NaxV2O5 is actually a crossover from two-dimensional to three-dimensional correlations, with interplanar correlations saturating at only ~150 Å, probably because of frustration. Such detailed insight into intercalant disorder is not possible by other methods.

What are the broader impacts of this work?
Intercalation compounds have potential as battery materials because of their rapid charging rates and stability over many charge-discharge cycles. Ordering of intercalants impacts battery performance by disrupting ionic mobility, and suppressing ordering can improve charging rates. The technique introduced here has the potential to measure for example lithium–lithium correlations in battery materials in spite of the low Li scattering cross section. Monitoring and understanding lithium–lithium correlations is crucial for the development of novel battery materials.

Diffuse scattering from Na0.45V2O5 in the Q=(H, 1/2, L) plane at 50 K (top) and the resulting deviation of the pair distribution function (PDF) from average, ΔPDF, in the (0yz) plane (bottom).
Diffuse scattering from Na0.45V2O5 in the Q=(H, 1/2, L)  plane at 50 K (top) and the resulting deviation of the pair distribution function (PDF) from average, ΔPDF, in the (0yz) plane (bottom).

Why did this research need CHESS?
This research required high dynamic range reciprocal space mapping, i.e. the capability to collect expansive diffraction data sets at high photon energies (27.3keV) with large area photon counting detectors (Dectris Pilatus 6 M) available at CHESS undulator beamline A2. The samples were continuously rotated in the beam at 1° per second over 370°, with images read out every 0.1 s. Similar experiments are now possible at the QM2 beamlines operated by the NSF-funded Center for High Energy X-ray Sciences (CHEXS) at CHESS.

Collaborators:

  • Matthew J. Krogstad, Materials Science Division, Argonne National Laboratory, Lemont, IL
  • MStephan Rosenkranz, Materials Science Division, Argonne National Laboratory, Lemont, IL
  • Justin M. Wozniak, Data Science and Learning Division, Argonne National Laboratory, Lemont, IL
  • Guy Jennings, Advanced Photon Source, Argonne National Laboratory, Lemont, IL
  • Jacob P. C. Ruff, Cornell High Energy Synchrotron Source, Cornell University, Ithaca, NY
  • John T. Vaughey, Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, IL
  • Raymond Osborn, Materials Science Division, Argonne National Laboratory, Lemont, IL

Publication Citation:
Krogstad, M.J., Rosenkranz, S., Wozniak, J.M.et al., “Reciprocal space imaging of ionic correlations in intercalation compounds,” Nat. Mater, Oct. 2019. https://doi.org/10.1038/s41563-019-0500-7

How was the work funded?
Experiments were performed at CHESS supported by NSF award DMR-1332208 and at APS supported by DOE under contract no. DE-AC02-06CH11357. Computational developments were supported by the Exascale Computing Project (17-SC-20-SC) through DOE and NNSA.