Pushing data quality for laboratory pair distribution function experiments

Abstract

Over the past decade, some studies with laboratory pair distribution function (PDF) data emerged. Yet, limited Q max 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 1 radiation, featuring a MYTHEN2 4K detector covering a Q range of 0.3–20.5 Å –1 . 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 6 . The high instrumental resolution is mirrored in low q damp values determined from LaB 6 measurements. PDF data from a powder sample of ca. 7 nm TiO 2 nanoparticles were successfully refined over up to 70 Å with goodness-of-fit values R w < 0.22 (respectively R w = 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.