Atomic-scale Structural Analysis by Total Scattering Profiles

Conventional X-ray diffraction primarily reveals the average crystal structure and long-range periodic order. Total scattering captures both Bragg diffraction and diffuse scattering, allowing analysis of local atomic arrangements, disorder, defects, and amorphous regions. This makes it possible to investigate materials whose functional properties depend on short-range structural variations that are not visible through conventional diffraction alone.

Atomic density can be determined by analyzing the total scattering structure factor and applying an iterative correction that removes non-physical modulations introduced during measurement. The corrected pair distribution function satisfies known physical constraints at very short atomic distances, allowing the average atomic density to be calculated accurately from scattering data and elemental composition without requiring bulk density measurements.

Bulk density measurements can be strongly affected by pores, voids, particle packing, and surface roughness. Total scattering instead measures the intrinsic atomic packing within the material itself, making it possible to determine microscopic density independently of sample morphology. This provides a more representative structural property for materials containing significant porosity or defects.

Reverse Monte Carlo modeling builds three-dimensional atomic configurations by repeatedly adjusting atomic positions until calculated scattering data matches experimental measurements. Rather than assuming a predefined structural model, it generates atomic arrangements that are consistent with the observed total scattering data, making it particularly useful for studying disorder, local distortions, and non-periodic structural features.

Traditional methods often require additional parameters describing instrument resolution or diffraction peak shapes, which can influence the final structural model. The proposed approach separates local and long-range structural contributions directly from the experimental total scattering data, eliminating the need for these ambiguous fitting parameters while accurately reproducing diffraction profiles. This simplifies the analysis and reduces user-dependent variability.

The method identifies local structural differences associated with different manganese oxidation states. Mn³⁺O₆ octahedra are found to have longer Mn–O bonds, larger bond-length distributions, and greater octahedral distortion than Mn⁴⁺O₆ octahedra. These local distortions provide insight into structural behavior associated with charge distribution, phase transitions, and battery performance.

Electrochemical performance depends not only on the average crystal structure but also on local atomic environments. Variations in bond lengths, bond angles, oxidation states, and octahedral distortions influence lithium diffusion, structural stability, capacity retention, and phase transformations during charge and discharge. Characterizing these subtle features helps researchers better understand battery degradation mechanisms and optimize cathode materials.

Reliable total scattering analysis requires measurements over a wide scattering-vector (Q) range, accurate background and Compton scattering corrections, and high-energy X-rays that extend the measurable Q range. High-energy laboratory sources, such as Ag Kα or Mo Kα radiation, provide sufficient resolution for accurate density determination and detailed local structural analysis, whereas lower-energy sources with limited Q range can introduce larger uncertainties.