Pushing data quality for laboratory pair distribution function experiments

Over the last decade, some studies with laboratory pair distribution function (PDF) data emerged. Yet, limited Q or instrumental resolution impeded in-depth structural refinements. With more advanced detector technologies, the question arose how to design novel PDF equipment for laboratories that will allow decent PDF refinements over r = 1-70 Å. It is crucial to reflect the essential requirements, namely, monochromatic X-rays, suppression of air scattering, instrumental resolution, and overall measurement times. The result is a novel PDF setup based on a STOE STADI P powder diffractometer in transmission-/Debye-Scherrer geometry with monochromatic Ag Kα radiation, featuring a MYTHEN2 4K detector covering a Q range of 0.3-20.5 Å. PDF data are collected in a moving PDF mode within 6 h. Structural signatures of liquids can be satisfactorily resolved in the PDF as shown for the ionic liquid hmimPF. The high instrumental resolution is mirrored in low q values determined from LaB measurements. PDF data from a powder sample of ca. 7 nm TiO nanoparticles were successfully refined over up to 70 Å with goodness-of-fit values R < 0.22 (respectively R = 0.18 over 30 Å), thanks to the low background and high instrumental resolution, hereby enlarging the accessible r range by several tens of Angstroms compared to previous laboratory PDF studies.