Raw Data

Measured intensities were collected using a Pilatus CdTe 2M detector (1679 × 1475 pixels, 172 × 172 µm² each) positioned with the incident beam in the corner of the detector. The sample-to-detector distance was approximately 0.3 m for the total scattering measurements.

Calibration is performed using NIST SRM 660b (LaB₆). Geometry calibration is performed using the software pyFAI followed by image integration including corrections for flat-field response, geometry, solid-angle, and polarization. All submodules have been calibrated to correct for small distortions of submodule positions, and a mask is applied to remove invalid pixels.

Integrated data

Raw data are integrated onto 3000 bin grid using a sigma_clipping algorithm to mask azimuthal outliers. The data are background subtracted and then corrected for parallax and offset error by a polynomial offset correction determined by Rietveld refinement of the LaB₆ structure with the known lattice parameter provided by the NIST certificate.

Rietveld refinement / Instrumental profile determination

Rietveld refinement is performed using TOPAS v7 to validate the geometry calibration, characterize the instrumental profile, and to determine the offset polynomial that is applied to all other datasets. We provide the input files that can be used as a starting point for refinement of further structures.

Data normalization and pair distribution function generation

The total scattering structure function F(Q) is generated using the program PDFgetX3 with appropriate composition and processing settings. The data are then Fourier transformed to get the PDF. Since it is generally good practice to assess the effects of the high-Q signal-to-noise on the resulting PDF, we process the data with several Q_max values as well as with and without modification function applied to suppress termination effects. Thus, all results can be cross-checked to validate features.

PDF refinement

Real-space refinement is also performed on the resulting data to ensure that the data correction is working properly and to validate the quality of the PDF data. Simple refinements are carried out using PDFgui. Features in the residual function are due to refinement with a simple model that assumes the Morningstar-Krutter-Warren approximation. A better result can be achieved using the Debye equation. A good result for LaB₆ gives an Rw of approximately 9%.

Data download structure

/references/pdf/

/samples/pdf/