Abstract:
Pair distribution function (PDF) analysis has emerged as a powerful technique for investigating the local atomic arrangements in crystalline, nanocrystalline, and amorphous materials. By utilizing total scattering data over a wide momentum-transfer range (Qmax), PDF analysis provides local structural information with high real-space resolution. At SPring-8, PDF measurements are currently available at several beamlines, including BL04B2, BL08W, and BL13XU. These offer diverse experimental capabilities for a broad range of materials research.
BL04B2 is a dedicated high-energy X-ray total scattering beamline and serves as the primary PDF beamline at SPring-8. [1] It has long been utilized for studies of structurally disordered materials and provides high-quality PDF data. BL13XU was originally designed for high-resolution powder diffraction experiments. However, its high X-ray energy enables access to high Qmax, making it suitable for PDF measurements. Owing to its excellent instrumental resolution, BL13XU is particularly advantageous for PDF studies of crystalline materials. Furthermore, BL08W employs a high-flux wiggler source and incident X-ray energies exceeding 100 keV to enable time-resolved PDF measurements. This capability has opened opportunities for in situ and operando investigations of structural changes occurring during chemical reactions and functional processes.
In recent years, PDF analysis has increasingly been applied not only to structurally disordered materials but also to a variety of functional crystalline materials. This trend is driven by a growing interest in understanding material properties that cannot be fully explained by average crystal structures alone, but instead originate from local distortions and short-range structural correlations revealed by PDF analysis. To meet this growing demand, the development of a PDF measurement system is currently underway at the Taiwan beamline BL12B2 of SPring-8. By utilizing 66 keV X-rays together with an EIGER2 area detector, PDF data with Qmax of approximately 22 Å⁻¹ can be collected within about 10 minutes. The small pixel size and excellent dynamic range of the detector provide high-quality data for both disordered materials and crystalline powder samples. Although further improvements in accessible Q range and background reduction are still required, these results demonstrate the feasibility of rapid PDF measurements at BL12B2. The system also shows promise for future time-resolved PDF experiments on the timescale of several minutes.
Several application examples will be presented to demonstrate the capabilities of PDF analysis. The first example is SiO₂ glass, one of the most fundamental amorphous materials. Even in the absence of Bragg diffraction peaks, PDF analysis provides valuable information on local atomic arrangements and serves as a powerful tool for structural characterization. Another example involves a mixed crystalline–amorphous Si–Ge system.[2] Through crystal PDF full-space refinement, minor crystalline phases can be quantitatively refined while simultaneously extracting the PDF contribution from the amorphous component. These examples illustrate how PDF analysis can provide structural insights that are difficult to obtain using conventional diffraction techniques alone.
This presentation introduces the current PDF measurement environment at SPring-8 and discusses the future potential of BL12B2 as a PDF platform available to Taiwanese users. The establishment of PDF capabilities at BL12B2 is expected to broaden opportunities for local-structure studies of both crystalline and non-crystalline materials.
Keywords – pair distribution function (PDF), high-energy X-ray total scattering, local atomic arrangements, synchrotron radiation